Finally starting on this convection oven -> reflow oven conversion project

[mindcrime]

I've had this Black and Decker convection oven sitting on a shelf for a month or more now, so tonight I finally decided to get started on the project. All (or at least most) of the parts I need have arrived now: I have an SSR for the mains power side, a couple of thermocouples and a thermocouple amplifier board to detect the temperature, and a linear actuator to open/close the door. I have plenty of microcontroller boards laying around, so I just need to decide what I want to use to run the thing.



The sacrificial lamb before the hacking begins.



Opened up and ready for surgery.



That red wire looks important.



The existing controls. Looks like I can mostly leave this stuff alone and just insert the SSR "upstream" so to speak. Worst case, if that timer doesn't have an "always on" position, I can bypass that.

Note to self: I should have powered this thing up and frobbed the controls a little before starting the surgery. That said, I still could since I haven't touched any of the wiring yet.

Edit: on second thought, I am going to need one or two more parts that I may not have lying around here already. I'll need an h-bridge motor driver so I can reverse the linear actuator. I'll also need a transformer to give me 12V that I can rectify to DC to use for the actuator. I may have that in the parts box already, not sure offhand.

And the datasheet for my SSR suggests adding a fast blowing fuse on the load side, so I'll probably have to pick up a fuse / fuse holder. Still, the major elements are all here. 

[fourfathom]

I have what looks like a similar oven I use for reflow.  It has heating elements above and below the racks.  I have a single sheet of aluminum in the middle position to hold my circuit board being reflowed.  I use a thermocouple attached to a chunk of circuit board, screwed to the aluminum tray.  I don't have a door actuator, but rely on me being there to open it during the cool-down cycle.

My controller is an arduino-style "ItsyBitsy M0", and it drives an optoisolated SSR between the wall power and the oven power cable.

My oven is un-modified, and I found that the heating and cooling rates with the heater 100% on and off were pretty close to the desired profile.  I have an auto-learning program that adjusts the on and off timing to hit my targets after a few calibration runs.  There is no fancy PID loop or proportional heat control, it's just on and off.  Here's the sequence:
Preheat: turn on the heat, wait until it reaches about 100 C.
Soak: Turn off the heater. The heat continues to rise, but slowly, almost flattening out after 60 seconds.
Reflow: Turn on the heater.  Temperature climbs.  Keep heat on until temperature reaches about 205 C (this value changes as a result of calibration runs)
Peaking: Turn off the heater.  The temperature continues to rise, peaking at about 230 C (my target for leaded solder)
Cooling:  Once the temperature drops a few degrees, buzz the alarm to tell me it's time to open the oven door.

I have the electronics in a small aluminum chassis, with a couple of buttons and a display, and I can control it with those.  I also have a USB serial-port interface which lets me control the thing from a program running on a PC -- this gives me nice charting and logging.  I also have duty-cycle heater control capability, and sometimes use that if I want to use the oven for medium-temperature thermal testing, but for soldering the on/off heater control works well.  Duty-cycle control would only slow down the heating ramp, and it's already barely fast enough.

[mindcrime]

I have what looks like a similar oven I use for reflow.  It has heating elements above and below the racks.  I have a single sheet of aluminum in the middle position to hold my circuit board being reflowed.  I use a thermocouple attached to a chunk of circuit board, screwed to the aluminum tray.  I don't have a door actuator, but rely on me being there to open it during the cool-down cycle.

I'm never going to run this thing when I'm not physically present, but the door actuator seemed prudent based on the experience a buddy of mine had with his oven. He found that his oven doesn't cool fast enough during the "cool" parts of the cycle, to track the temperature profile well. He could only get the cooling to be fast enough by opening the door.

My controller is an arduino-style "ItsyBitsy M0", and it drives an optoisolated SSR between the wall power and the oven power cable.

Hmmm... opto-isolation, that's probably a good idea. I should do that. Glad you mentioned that.

My oven is un-modified, and I found that the heating and cooling rates with the heater 100% on and off were pretty close to the desired profile.

Gotcha. Other than the door actuator (and adding thermocouples), I don't plan to modify the core of the oven itself. It's all about switching the power on and off as needed through the SSR.

I have an auto-learning program that adjusts the on and off timing to hit my targets after a few calibration runs.  There is no fancy PID loop or proportional heat control, it's just on and off. 

I thought about going that route as well, but this is as much a didactic exercise for me as it is just a tool building exercise, and I've always wanted to learn more about control theory, so I think I'm going to go the PID route. Although once all the "pieces" are in place (thermocouples, door actuator, SSR), then I can tweak everything else through software, so I may experiment with different algorithms and approaches as I learn more about control theory.

I have the electronics in a small aluminum chassis, with a couple of buttons and a display, and I can control it with those.  I also have a USB serial-port interface which lets me control the thing from a program running on a PC -- this gives me nice charting and logging.  I also have duty-cycle heater control capability, and sometimes use that if I want to use the oven for medium-temperature thermal testing, but for soldering the on/off heater control works well.  Duty-cycle control would only slow down the heating ramp, and it's already barely fast enough.

Sounds pretty close to what I'm planning. I definitely want to support data logging / control via a PC. I might use wifi for the connection instead of a USB cable though. Heck, I could even experiment with using Bluetooth, I suppose.

That said, I like the idea of having a display and some sort of input mechanism right on the oven... at the very least I'd like  a way to select which temperature profile to run, a "start" and "stop" button, and a display of the instantaneous temperature in the oven.

That's an interesting thought about using the oven for thermal testing, and possibly other uses, besides just for soldering.  I hadn't even considered it having any application besides soldering (and learning control theory stuff).

[rstofer]

I used this controller.  I remounted the display in a metal box mounted above the oven.  Clean installation.

https://www.rocketscream.com/blog/product/tiny-reflow-controller/

That version is retired, the new version is:

https://www.rocketscream.com/blog/product/tiny-reflow-controller-v2/

I installed the Solid State Relay in the right hand sidewall.  I also added high temperature mat insulation in the various cavities.  Without the insulation, I couldn't get up to temperature fast enough.  McMaster-Carr carries it but I don't remember which variant I used:

https://www.mcmaster.com/insulation/insulation-for-equipment-ovens-and-furnaces/

My oven is based on the Black & Decker InfraWave toaster oven.

[fourfathom]

Yes, if you leave the oven door closed after the end of the reflow stage you will never get close to a recommended cool-down rate.  I might eventually add a door-opener.  Another option is to add an air duct and a blower, but that probably adds other thermal complications.  With my beeper alarm the system works well enough for now.

I've been asked to write up my toaster reflow, and when I've collected the data will post more here.  I've also hacked into a "Reptile Incubator" Thermal Chamber (see eevblog video: ), modifying it and adding an external controller (much like my toaster-reflow project).  This does used a PID control loop, and I'm writing that one up as well.

[mindcrime]

https://www.rocketscream.com/blog/product/tiny-reflow-controller-v2/

Nice, I'll have to check that out.

I installed the Solid State Relay in the right hand sidewall.

Yeah, that's pretty much what I'm planning on as well.

I also added high temperature mat insulation in the various cavities.  Without the insulation, I couldn't get up to temperature fast enough.  McMaster-Carr carries it but I don't remember which variant I used:

There's some firewall insulation that race-car builders use that I'm familiar with, I was thinking of using that if I need extra insulation. Not sure if it's more or less the same stuff or not. I may even be able to get some for free, if my dad (who builds race cars) has some scraps laying around his shop. I'll have to ask next time I talk to him.

[Miti]

From my experience with toaster ovens, they never cool down fast enough, even when the door is fully open. The reflow profile is at the board level, not the air inside the oven. If you attach a thermocouple to the board, you’ll see that it stays at dangerous high temperatures for way too long if you don’t blow air on it.

[mindcrime]

From my experience with toaster ovens, they never cool down fast enough, even when the door is fully open. The reflow profile is at the board level, not the air inside the oven. If you attach a thermocouple to the board, you’ll see that it stays at dangerous high temperatures for way too long if you don’t blow air on it.

Blimey. Well, worst case, I can always bodge in a blower of some sort of push in cool air from outside the oven.

[fourfathom]

I just ran some tests with my un-modified Black & Decker toaster oven:

Reflow cycle, door opened after peaking


Door remaining closed

I'm fairly comfortable with the cool-down when I open the door.  This is in a garage, fairly cool but no particular airflow.  I also think that the pre-heat, soak, and reflow are reasonable.  I'm using a leaded solder paste and have a reflow target of 230 deg C.  Perhaps with added insulation the cool-down might not be as rapid?

(is image in-lining still not working?)

[coppercone2]

if you open the door it won't be so bad.

[fourfathom]

if you open the door it won't be so bad.

If you're referring to my charts above, in the first one I do open the door after temperature peaking, and indeed, it's not so bad.  The other chart shows the temperature profile with the door kept shut, and I agree, it stays too hot for too long.  BTW, The temperatures shown are measured by a thermocouple that is attached to a small circuit board located adjacent to the board being soldered.  This is the sensor that my program is monitoring.

[coppercone2]

I did similar experiments with my PID oven, mine is a multi zone controller or whatever that can turn on a cooling system, but I have not done it. I thought to put a blower fan on top and channel it in, but I think its good enough when you open the door. you could just put a dryer flap on it so when you turn on the fan it opens the flap and cools the oven quickly, you need 2, one to protect the fan, and the other to open the oven.

but its a fair bit of sheet metal work because I don't want hot air shooting out of the side of the thing, I would need to make a diffusor system so when I leave something on top of it, the damage is not catastrophic

if you want a 'nice' mod, you need to do this on top of the oven, and figure out the correct springs, and install duct on double wall thin sheet metal.. its a fair bit of work.

I used a expensive SSR for mine ($60) because the parts I put in there can easily be a couple of hundred dollars, so its pointless to go with china reliability here, since I am not drying painted door handles.. personally to me a ruined pizza bagel is enough of a problem I don't want to go to china. Seriously when you pop something complicated into the toaster oven chances are you are tired as hell and going to be mega pissed off if it burns food lol..


They are useful also for doing things with varnish, I varnished my transformer in it from a HP supply to stop buzzing, after vacuum impregnation, since you can set the temp precisely to datasheet parameters.

I am super interested in high quality pizza bagels though, I wonder how much customers they lose because of bad thermal control. I have no idea how such a good food got a reputation along the lines of a pop tart.

Also getting a steady flow inside of the thing to cool it down nicely without thermal gradients is gonna be hard, because if you spot cool it with air flow you can break parts. I think basically opening the door is the safest option. They sell a nice D-cell powered fan for 25$ you can set next to the oven, open the door and turn the fan on to blow into it, it lasts a long time on a set of D's, does not have a cable and you can put it far away enough to cool the board gently.

What might be best is another chamber called a cooling chamber, so you take the board out when its solid and put it in there with something designed for cooling rather then heating!


I think I will use an AUX on the pid controller to sound a buzzer and turn on a light when it detects the solder is solid and then make a cooling box some how.

Keep in mind too those elements will last shorter if you cool them fast, so its probobly better not to even do cooling in the oven, and close the door after you take the board out to cool off.

[Miti]

I just ran some tests with my un-modified Black & Decker toaster oven:

(Attachment Link)
Reflow cycle, door opened after peaking

(Attachment Link)
Door remaining closed

I'm fairly comfortable with the cool-down when I open the door.  This is in a garage, fairly cool but no particular airflow.  I also think that the pre-heat, soak, and reflow are reasonable.  I'm using a leaded solder paste and have a reflow target of 230 deg C.  Perhaps with added insulation the cool-down might not be as rapid?

(is image in-lining still not working?)

More than 2 minutes above 200 C?  Good luck!

[fourfathom]

More than 2 minutes above 200 C?  Good luck!

When I open the door after peaking I'm only above 200 C for 90 seconds.  Perhaps you're looking at the "door closed" profile, where I delay opening the door until long after cool-down in order to show why you need to open the door?

[johofz]

I just recently converted a similar oven into a reflow oven. It has a hole on the top originally used to grill stuff on a plate you can put there. This is very convenient, since you can open the door aswell as the hole on top to cool down very fast. The only thing is, that it needs some thermal isolation to increase dT/dt for the soldering phase.

Here is my repository for the Hardware and Firmware:
https://github.com/johofz/Reflow_Oven_V2

I did a V2 because I had some issues with power dissipation and wanted a bigger touchscreen. I choose a rather beefy STM32f415 in LQFP-100 package, since they have FSMC and I wanted to use a 16-bit parallel 3.2" TFT with a touchscreen.

I can share some pictures and graphs if someones Interested.

It can also be used to heat things to a controlled temperature. It can keep temperatures stable as low as 10°C above room temperature.

I didn't had the time to test the reflow part yet, but I will shortly recive some PCBs and will share the results once I'm done.

[mindcrime]

Project update 05-01-2021 (repost due to database issues blowing away previous posting)

I spent some time a couple of days ago working with the thermocouple amplifier I am planning to use, and the thermocouple, making sure I could get useful temperature readings with the Arduino. That part is handled now, so the next major task is to sort out switching the power on and off with the SSR. I didn't want to start messing with the wiring inside the oven itself yet, so in order to start experimenting with the SSR (and leave myself with a possibly useful gadget) I took a sacrificial extension cord and one of the extra SSR's I ordered, and built this:





So far this works a treat, although the only load I've used is my desk lamp. That's fine, the principle is the same. The issue here is that I've realized that I'm going to need a couple more parts to make all of this work. The minimum rated voltage for the control signal on this SSR is 4VDC, and my arduino is a 3.3V unit. So I'm going to need a separate power rail (also needed for the linear actuator) and a transistor to control the SSR.

My current (no pun intended, hahaha) thinking is to add a transformer to step the 120VAC mains current down to 12VAC, then a bridge rectifier to give me 12VDC. That should serve just fine for the linear actuator, and I can probably just use 12V for the SSR control as well. It's rated from 4-30V so that should work. Or I can always add a linear regulator or a buck converter to give me 5V or whatever.  Actually come to think of it, I think I'll need a low voltage rail to power the Arduino anyway.

I also recently realized I'll need an h-bridge for the linear actuator. And the production version of this will use opto-isolation on the SSR control, and a fast blowing fuse on the load side of the SSR.  So despite my laughable assertion earlier that "all the parts I need are here", I now find myself waiting for a box from Jameco with the transformer, h-bridge, opto-isolators, fuse holder, rectifiers, etc. Not a ton I can do until then. I may also add a manual toggle switch upstream of everything else on the mains input.

[mindcrime]

Project Update 05-09-2021

OK, making more good progress on this. I have the arduino now controlling the SSR, by using a little SN2222 as a driver for the SSR, and an independent 12V power supply for the relay. I didn't do all the stuff with the transformer and rectifier yet, rather I just used my bench power supply for that for now. Nonetheless, now the 3.3V digital pin on the Arduino can turn the SSR on and off with no problems. So now I've combined that and the thermocouple stuff, and today for the first time I plugged the actual oven into the SSR instead of my desk lamp "dummy load".

I wrote code to turn the oven on, monitor the temp, and then turn it off once it hits a certain temp. This is not any actual soldering profile, but just a proof of concept to convince myself that I can detect the temperature in the oven and turn it on and off in response.

Here's a sample of the output from the serial monitor with the thing running:

Code: [Select]

MAX31856 thermocouple test
Thermocouple type: K Type
C = 22.0
F = 71.7
Turning OVEN on
C = 44.1
F = 111.4
monitoring OVEN
C = 44.1
F = 111.4
monitoring OVEN

<snip>

C = 89.9
F = 193.9
monitoring OVEN
C = 89.9
F = 193.9
monitoring OVEN
C = 90.0
F = 194.0
Turning OVEN off

Next steps now:

1. Build the power-supply that will live inside the oven to power the SSR, power the Arduino, and power the door actuator.
2. Wire up the door actuator controls to the arduino and get code written that can open and close the door.
One open issue I have here is figuring out the door position at a moment in time, so I don't try to drive it beyond it's range of motion. Since the linear actuator works at fixed speed, I could just "do the math" and not worry about measuring the door position empirically. Or... dunno. Haven't given this part a ton of thought yet, TBH.
3. Physically attach the actuator to the oven and couple it to the door.
4. Provide a way to store and identify particular temperature profiles.
5. Implement PID in software (probably using a library of some sort, not necessarily going to try to write PID from scratch) to try and match the selected temperature profile.
6. Test it by baking some boards.
7. Add a little LCD display or something to show the selected profile, instantaneous temperature, elapsed time, etc.
8. Implement a keypad control or something to select a profile, as well as "go" and "stop" buttons.
9. Package everything up neatly and close the case up.

That's probably missing a few things. I may need to fiddle with adding insulation, sealing air leaks, etc., if my  one buddy's experience is any indicator. And who knows, maybe I'll need to add a fan/blower of some sort to get the cooling to happen fast enough. Time will tell on that part, I suppose.

[Miti]

Take a look at this project:

https://apollo.open-resource.org/mission:resources:picoreflow

I tried it, it works well but my oven cannot follow the profile, I did not bother insulating it. In the end, I’m controlling it manually, with a low mass thermocouple connected to the board. I turn it fully on up to 150 C,
about 25% duty cycle to 180 C, then fully on to 215 C, this is for leaded, I don’t use lead free with my projects. After about 10 second I open the door and use a 120mm fan to blow air from about half a meter or more so I don’t cool it down too fast. This method never failed me for years. I thought about coding this in an Arduino but I couldn’t find the motivation. I bought recently a T962 for 120CAD but it’s a piece of crap. The temperature difference between left and right is about 10 C.

[mindcrime]

I bought recently a T962 for 120CAD but it’s a piece of crap. The temperature difference between left and right is about 10 C.

Funny you mention that... one reason I decided to go the DIY route - aside from it being a learning experience in and of itself - is that a buddy of mine had a T962, and then did a convection oven conversion, and ultimately found that his converted convection oven did a better job than the T962. In the end, I think he donated the T962 to the hackerspace where we were both members and kept his DIY oven in his lab for his own use. I haven't heard a lot of good things about those cheap Chinese made reflow ovens, and the conversion project looked fun and not too expensive, so here we go...

[phil from seattle]

Wire up the door actuator controls to the arduino and get code written that can open and close the door.
One open issue I have here is figuring out the door position at a moment in time, so I don't try to drive it beyond it's range of motion. Since the linear actuator works at fixed speed, I could just "do the math" and not worry about measuring the door position empirically. Or... dunno. Haven't given this part a ton of thought yet, TBH.

One possibility is to use a hobby servo.  Because you command it to a specific position, you will never over drive it or position it in the wrong spot. Plus, you can use the PWM hardware of the arduino so there is no software overhead to maintaining a position.  They make all sorts different kinds of servos and they are farily inexpensive.

[mindcrime]

Project Update 05/12/2021

Made some solid progress tonight. I have the low voltage power supply pretty much finished. It's nothing fancy, just a transformer, a bridge rectifier, a couple of LM78xx series regulators (one for 5V, one for 12V) and a few capacitors. But it should serve my needs.

[beanflying]

You might get some ideas from this Coffee Roasting firmware/hardware including PCB shield for SSR and fan controls. Coffee Roasting and PCB ovens share a similar temperature controlled ramp soak and rapid cooling process. In particular look at the slow PWM part of it to drive the SSR. https://github.com/greencardigan/TC4-shield People have used small turbo ovens with a Rotisserie and drum for roasting but the standard mod was always Insulate the body for better stability and control and generally adding some airflow from adding a fan and exhaust.

greencardigan is a member here too.

[mindcrime]

You might get some ideas from this Coffee Roasting firmware/hardware including PCB shield for SSR and fan controls. Coffee Roasting and PCB ovens share a similar temperature controlled ramp soak and rapid cooling process. In particular look at the slow PWM part of it to drive the SSR. https://github.com/greencardigan/TC4-shield People have used small turbo ovens with a Rotisserie and drum for roasting but the standard mod was always Insulate the body for better stability and control and generally adding some airflow from adding a fan and exhaust.

greencardigan is a member here too.

Radical! I had no idea that roasting coffee beans was at all similar to reflow soldering. Maybe this oven *will* turn out to have multiple uses in the end.  Of course this one will probably wind up contaminated by soldering byproducts, so if I wanted to roast my own beans, I'd probably build another one. Just to be on the safe side.

I decided to go ahead and operate on the assumption that extra insulation will ultimately be useful, so I ordered some of this stuff from Amazon. So hopefully it will do the job as far as further insulating the internal cooking chamber.

[wizard69]

This is an interesting thread that I just dropped into.   I have not built a reflow oven yet as I'm thinking more along the lines of a multiple use oven.   However some comments from working on industrial ovens of various types over the years:

• First insulation is your friend.    One of the gotchas with conversions is making sure the oven is easy to insulate.   It makes a huge difference in the temperatures you can achieve and the power you will use to get there.
• If you are going to use SSR you might as well buy an optically isolated one.   More so I believe that most on the market are isolated in some manner.
• Air circulation can make a huge difference in the ultimate oven temperature profile.   It can also be integrated into the cooling profile.
• If you don't have air circulation consider the aluminum plate somebody mentioned above.
• Make sure your wires are temperature rated for the location they are in.
• Be careful not to disable any over temp safeties built into the oven or provide your own.   This is extremely important for safety.   These ovens can get very hot in some cases even over the course of a trip to the bathroom.   The alternative is to implement your own, which in some cases is a better idea.
• A door switch can offer up additional safety, if designed to shut off heater power on door opening.   This may be an issue with fan based cool downs though.
• Don't assume that the unit will never be run unattended, thus design in safety in case something of higher priority comes up and you get distracted.   Your best intentions can be trumped by a kid crashing a bike and bleeding all over or the wife saying her water broke and you need to go to the hospital.   Or if you are like me you can some times just focus on something to the exclusion of the entire world and forget what is going on.   This goes back to over temp protection and frankly a limit on cycle time.
• Kinda related to the above add a buzzer or bell to alert you to the end of cycle or other program steps.   You might not need it all the time but it can really help when developing recipes and doing things like manually opening the door.
• Data logging can be a great diagnostic tool.   Even if it is a file on secondary storage that get over written with each run, it can be a bit help.   So consider that when writing your oven control software.   The only trick here is to find the right sample time to catch glitches yet not blow up file size.
  
  In the industrial world this has made what might have been a difficult to solve issue a simple task of reading a file and seeing what happened.   At the very least you want time and temperature data but the more the better though "more" gets into a lot more control hardware.

Hope this helps some.

[mindcrime]

• First insulation is your friend.    One of the gotchas with conversions is making sure the oven is easy to insulate.   It makes a huge difference in the temperatures you can achieve and the power you will use to get there.

That definitely jibes with my one buddy's experience, as well as what I've heard from others here. I just got  a couple of sheets of that aluminized fiberglass insulation that they use for race car firewalls, so we'll see how well that works out.

• If you are going to use SSR you might as well buy an optically isolated one.   More so I believe that most on the market are isolated in some manner.

Ah. Had I thought about that earlier, I would have done so. But I already have the SSR I plan to use, and it's not explicitly opto-isolated AFAIK. I do however, have standalone opto-isolators that I plan to incorporate.

• Make sure your wires are temperature rated for the location they are in.

Definitely. In addition I got some high temperature insulated wire sheath material to use anywhere I have to route wires where they might be exposed to a lot of heat.

• Don't assume that the unit will never be run unattended, thus design in safety in case something of higher priority comes up and you get distracted.   Your best intentions can be trumped by a kid crashing a bike and bleeding all over or the wife saying her water broke and you need to go to the hospital.   Or if you are like me you can some times just focus on something to the exclusion of the entire world and forget what is going on.   This goes back to over temp protection and frankly a limit on cycle time.

Agreed. I expect I'll incorporate both an over-temp limit and a maximum cycle time.

• Kinda related to the above add a buzzer or bell to alert you to the end of cycle or other program steps.   You might not need it all the time but it can really help when developing recipes and doing things like manually opening the door.

Agreed. A nice, loud bell or chime of some sort should be there. I hadn't planned on that initially so I didn't buy a part for that yet, but it should be easy enough to find something suitable.

• Data logging can be a great diagnostic tool.   Even if it is a file on secondary storage that get over written with each run, it can be a bit help.   So consider that when writing your oven control software.   The only trick here is to find the right sample time to catch glitches yet not blow up file size.
  

The tentative plan as of right now is to push logging / telemetry data to a server on my network.

[mindcrime]

Project Update 05-14-2021

I decided to punt on the door control stuff for a moment, and focus on the interactive control elements. So I rigged up a 12 button keypad and a little 20x4 LCD display, and got that working with the Arduino to the point that I can get an interrupt when a key is pressed on the keypad, read the current key, stick it in a buffer, and repeat until I get the command delimiter ('#').  Right now I'm envisioning the command protocol being pretty basic. Something like:

• n# for n = 1 - 9 or so -  means "Run Profile n"
   
• 99# - means "abort current run and reset"

That may literally be it. I'm not sure if there are any other commands I would even need. Also, I'll have the LCD displaying some basic information like the currently running profile, current temperature, elapsed time, etc.

Also, a random thought occurred to me while working on this: I've always meant to learn to work with those IR remote controls, so I'm now toying with adding the ability to control this thing with a universal remote. 

Some pics of the work in progress:











A little commentary on that last picture - the IC on the right hand side of the breadboard is a 74C922 decoder, which translates the keypad button presses into a 4 binary digit signal which is then sent to the μ-controller. The other IC is a 74HC04 quad inverter. It's there to push the OE pin of the 922 low when the DA pin goes high.

The code running on the μ-controller attaches an interrupt handler to the digital pin that DA (Data Available) is connected to, and when it fires it reads one binary digit from each of the four data bus lines, then converts that to its integer form. Inputs are pushed into a fixed length buffer until either the buffer max length is reached with no terminator encounter (in which case the buffer is cleared and the previous input is assumed to be invalid), or the code mapped to '#' is encountered.  Once we see a '#', a flag is set that tells the main loop "it's OK to read the input buffer and process it now".  The rest remains to be implemented, but what will come next is the "run profile n" stuff and the actual temperature profile control logic (TBD).

[coppercone2]

I had to buy fiber glass silicone wire (the same kind as in the oven) to make the power and fan control extensions to my control  box which was bolted to the side of the top chassis. I usex like a 10x10x5 box on the side, and the lid of the box I made from 3/16 thick preforated steel sheet, so the PID and SSR are sure to get good cooling (like old HP equipment, but bigger preforations since its a power device without a internal heatsink).

Don't miss the detail, match the same type of wire they have in the oven side cabinet to the wire you are leading out, it gets pretty hot. They used the same type of wire for everything in mine, including the low power fan, until it got to a distribution block inside of the metal box, where I switched to conventional wire, since that are does not get hot.

Because I was too cheap to get a big base plate, to get stiff/ridgid mechanical assembly, its built for service by a octopus (i.e. mirrors and right angle key to service some things), thankfully my PID comes in a sleeve so theoretically I can swap out every part without undoing the wires, so long nothing in the oven breaks, then I will be cursing hard, well maybe if it broke right after I made it, but its been a year so I think I won't be too upset doing a bit of difficult disassembly.

[mindcrime]

I had to buy fiber glass silicone wire (the same kind as in the oven) to make the power and fan control extensions to my control  box which was bolted to the side of the top chassis. I usex like a 10x10x5 box on the side, and the lid of the box I made from 3/16 thick preforated steel sheet, so the PID and SSR are sure to get good cooling (like old HP equipment, but bigger preforations since its a power device without a internal heatsink).

Don't miss the detail, match the same type of wire they have in the oven side cabinet to the wire you are leading out, it gets pretty hot. They used the same type of wire for everything in mine, including the low power fan, until it got to a distribution block inside of the metal box, where I switched to conventional wire, since that are does not get hot.

Because I was too cheap to get a big base plate, to get stiff/ridgid mechanical assembly, its built for service by a octopus (i.e. mirrors and right angle key to service some things), thankfully my PID comes in a sleeve so theoretically I can swap out every part without undoing the wires, so long nothing in the oven breaks, then I will be cursing hard, well maybe if it broke right after I made it, but its been a year so I think I won't be too upset doing a bit of difficult disassembly.

I went with this stuff https://iseinc.com/_shop/16-awg-tggt-high-temperature-hook-up-wire.html for wire. And it will be routed inside an additional insulating sheath as well.

[coppercone2]

That is similar, but I went with color coding and 12awg for a premium lol,

you can put heat shrink on the ends of the wire going into the chassis with the correct color code

[mindcrime]

That is similar, but I went with color coding and 12awg for a premium lol,

you can put heat shrink on the ends of the wire going into the chassis with the correct color code

Yeah, I was actually looking for colored wire, but was having trouble finding the right combination of temperature range, price, availability, and available colors. Most of the colored stuff I found was only available in spools of 100' and were in "not stocked" status anyway. This stuff seemed like a decent enough compromise. I like your idea about tagging the ends with some heat shrink tubing. That will definitely help keep things straight.

Edit: I found some black high-temp wire for a reasonable price as well, so now I have two colors.  Should be sufficient. I think the only long runs of "extra" wire I will have will largely be to the door actuator.

What I might have to do, is work out a way to add an extra little heat shield or something, to protect the PCB, the micro, and the small amount of wiring that will live in the right-hand side of the case. There are already vent scallops on the back wall of the case there, so adding a fan for that section might be a good idea as well.

[fourfathom]

Here is the profile I get with my un-modified two-element toaster oven, this time with some gentle fan-driven airflow during the cool-down portion.  Also, the suggested profile from the ChipQwik datasheet (Sn63/Pb37).  My time above 183 deg C is still a bit long (120 sec vs the suggested 90 sec), but it's been working well for me. 

You can see my heater on/off control on the chart as well as the temperature.  As I mentioned, I didn't see any reason for duty-cycle control of the heat, as full-on / full-off seems the best when trying for rapid heating and cooling.  My control parameters are shown on the left of the chart: 
For the preheat I turn on the heat elements. 
When the temperature reaches 100 C, I turn off the heat for 60 seconds and start the soak cycle.  The temperature continues to rise.
At the end of the 60 second soak phase the temperature is at 150 C and I turn the heat back on and start the reflow stage.
I turn off the heat when the temperature hits 215 C, and the temperature continues to increase, peaking at the desired 235 C.
When the temperature falls by one degree I sound the buzzer and I manually open the oven door.
Here, I have a small fan that blows ambient air into the oven chamber.  This speeds up the cooldown phase.

[mindcrime]

Hey @fourfathom, thanks, that helps a lot. I'm just  starting to get some temperature ramp up data from mine, so it will be nice to have something to compare against. 

I did a test run just now, where I had the micro turn the oven on, and ramp it all the way up to 250° C, then turn it off, all while spitting out the elapsed time and temperature every two seconds. I have the raw data, but haven't had time to graph it or do any math on it yet, to see how close to linear (or another shape) the curve is. I'll probably work on that this weekend, along with more testing.

This is with no additional insulation added, and with the outer cover off the case. Putting the cover back on and adding insulation would almost certainly give it a faster ramp up, but not sure if the extra insulation will prove necessary or not. Note: times are elapsed time since the oven was turned on, in milliseconds. So it takes about 112 seconds to reach 150° C, and about 290 seconds to reach 250° C.

Unfortunately I forgot the logging code in the branch after the oven is turned off, so I didn't get any data on the cool-down period. That will have to wait for this weekend.

Code: [Select]

MAX31856 thermocouple test
Thermocouple type: K Type
Turning OVEN on
6094,38.70
8095,38.74
10096,38.92
12097,39.48
14098,40.01
16099,40.76
18100,41.38
20101,42.32
22102,43.68
24103,44.92
26104,46.48
28105,48.45
30105,50.43
32107,52.88
34108,55.23
36109,56.72
38110,58.66
40110,60.77
42111,62.39
44113,64.33
46114,66.89
48115,69.15
50116,71.81
52117,74.73
54118,77.52
56119,80.40
58120,83.06
60121,85.89
62122,88.76
64122,91.73
66123,94.66
68124,97.58
70125,99.91
72126,102.75
74127,105.54
76128,108.15
78129,110.71
80130,113.55
82131,115.97
84132,118.54
86134,120.90
88135,123.23
90136,125.71
92137,128.09
94138,130.46
96139,133.08
98140,135.23
100141,137.30
102142,139.69
104143,142.20
106144,144.77
108145,147.09
110146,149.40
112147,151.77
114148,153.75
116149,155.80
118150,157.81
120151,160.20
122152,162.41
124153,164.43
126154,165.95
128155,167.55
130156,169.28
132157,171.14
134158,172.90
136159,174.64
138160,176.48
140161,178.12
142162,179.54
144163,180.73
146164,182.05
148166,183.74
150167,185.57
152168,187.45
154169,189.18
156170,190.81
158171,192.52
160172,194.12
162173,195.80
164174,196.96
166175,198.50
168176,199.80
170177,200.97
172178,201.88
174179,203.13
176180,204.23
178181,205.58
180182,206.45
182183,208.28
184184,209.75
186185,210.84
188186,212.09
190187,212.93
192188,214.21
194189,215.20
196190,215.73
198191,216.87
200192,218.16
202193,219.02
204194,220.09
206195,220.93
208196,221.87
210197,222.83
212199,223.62
214200,224.29
216201,224.83
218202,225.88
220203,226.89
222204,227.71
224205,229.41
226206,230.29
228207,230.56
230208,231.59
232209,232.15
234210,233.00
236211,233.88
238212,234.80
240213,235.68
242214,235.87
244215,236.47
246216,237.03
248217,237.43
250218,237.94
252219,238.37
254220,238.89
256221,239.70
258222,240.63
260223,241.34
262224,241.95
264225,242.40
266226,243.06
268227,243.29
270228,243.59
272229,244.30
274230,244.66
276231,244.95
278232,246.23
280233,247.23
282235,247.55
284236,247.79
286237,248.37
288238,249.31
290239,250.00
Turning OVEN off


[fourfathom]

Since I'm turning the heater on / off / on / off, I can't compare your ramp-up rate exactly, but if we look at the time it takes to go from 75C to 100C (my heater has probably stabilized at full-output during this interval), my oven takes 20 seconds, and yours takes 18 seconds.  The ramp from 175C to 220C  Takes mine 30 seconds, and yours 31 seconds.  And I'm just eyeballing this from my chart (I didn't have the logging turned on), I'd say we're pretty close.

[mindcrime]

Did some more temperature profiling tonight. Not trying to match a published profile yet, just some "ramp to peak / ramp down" stuff, with the door both closed and open during the ramp down period. Captured all the data this time and got some decent plots. So far I'd say this looks encouraging. I don't think I'll have too much trouble getting this to match the various solder profiles to within the allowed variance.

[See attachment images below]

Also, here are some random pics of the testing in progress, as this all starts to come together. Soon I need to go ahead and start looking at how to mount the various components in the case (whichever ones are going in the case anyway), so I can button this up and do some testing with the cover on. I also need to integrate the keypad/LCD stuff I did, come up with some kind of enclosure for those parts, and figure out how to mount that. Right now I think I'm going to leave the door actuator stuff for the very end. It's pretty simple conceptually, and I need the outer case cover on when I mount the actuator anyway.











Also, if anybody is wondering "Why is there a piece of cloth under a toaster oven that's heating up to 250° C?" the answer is... there isn't. That grey thing is a carbon fiber welder's blanket.

[ Specified attachment is not available ]

[fourfathom]

Good progress!  I would be interested in the temperature ramp after you turn off the heater.  On mine, the temperature continues to rise for quite a while.

[mindcrime]

Good progress!  I would be interested in the temperature ramp after you turn off the heater.  On mine, the temperature continues to rise for quite a while.

Yes, I also see the temperature continue to rise at least briefly, after turning off the elements. Hence the overshoot which I think is visible even in the plots. Here's the raw data around that point in the process, with the point where the elements are turned off marked.

Code: [Select]

0,29.21
2,29.25
4,29.25
6,29.21
8,29.21
10,29.23
12,29.30
14,29.44
16,29.68
18,29.91
20,30.30
22,30.75
24,31.33
26,31.98
28,32.79
30,33.71
32,34.79
34,35.91
36,36.99
38,38.45
40,39.77
42,41.46
44,43.19
46,44.95
48,46.70
50,48.57
52,50.59
54,52.70
56,54.86
58,57.18
60,59.40
62,61.76
64,64.00
66,66.50
68,69.02
70,71.49
72,74.17
74,76.94
76,79.66
78,82.38
80,85.20
82,88.01
84,90.89
86,93.78
88,96.70
90,99.67
92,102.68
94,105.45
96,108.47
98,111.59
100,114.45
102,117.34
104,120.23
106,123.29
108,126.22
110,129.09
112,131.96
114,134.71
116,137.52
118,140.55
120,143.35
122,146.27
124,148.97
126,151.77
128,154.49
130,157.11
132,159.80
134,162.45
136,165.24
138,168.12
140,170.59
142,173.07
144,175.52
146,178.14
148,180.67
150,183.06
152,185.30
154,187.61
156,190.00
158,192.35
160,194.48
162,196.81
164,199.04
166,201.21
168,203.29
170,205.52
172,207.52
174,209.66
176,211.77
178,213.76
180,215.70
182,217.84
184,219.87
186,221.84
188,223.83
190,225.77
192,227.60
194,229.45
196,231.41
198,233.20
200,234.97
202,236.46
204,238.06
206,239.95
208,241.79
210,243.52
213,245.16
215,246.80
217,248.16
219,249.65
221,251.42 # elements turned off here, as soon as temp > 250.0
223,252.95
225,254.27
227,255.27
229,255.77
231,256.19
233,256.43
235,256.75
237,257.18
239,257.54
241,257.59
243,257.71 # temperature peaks here, 22 seconds after the elements are turned off
245,257.67 # and declines from here on
247,257.34
249,257.02
251,256.62
253,256.20
255,255.62


[beanflying]

Unlikely it is the bead type thermocouple lagging so it is more just a case of some thermal inertia carrying you past what you are aiming for. In Coffee Roasting we have a different set of issues as the beans go exothermic during the roast but if we need to bring the ramp down a quick blip of air through the chamber is way faster than waiting for the Element and Metal/Bean mass to respond.

Is your code written to work from actual temperature data only or does it look at a Rate of Rise/Fall as well? RoR or some sort of Temperature average over a few seconds is sometimes a better thing to run from.

[fourfathom]

Interesting.  Your peak happens 22 seconds after the heater is turned off, and mine (215C to 232C) takes 45 seconds.  No doubt the absolute and ambient temperatures makes a difference, as does the fact that you have removed the sheet-metal oven cover.  I also see a peaking difference in my oven when I start with the thing at ambient (the first run), compared to when in between cycles I only let it cool to 50C or so.

[mindcrime]

Unlikely it is the bead type thermocouple lagging so it is more just a case of some thermal inertia carrying you past what you are aiming for. In Coffee Roasting we have a different set of issues as the beans go exothermic during the roast but if we need to bring the ramp down a quick blip of air through the chamber is way faster than waiting for the Element and Metal/Bean mass to respond.

Is your code written to work from actual temperature data only or does it look at a Rate of Rise/Fall as well? RoR or some sort of Temperature average over a few seconds is sometimes a better thing to run from.

The current code is only looking at the actual instantaneous temperature, but I haven't even started seriously trying to implement the code to actually track real temperature profiles yet. I just wanted to get some raw data to see if the oven can fundamentally heat up and cool down fast enough to accomplish the job at hand. My tentative plan is to implement PID control eventually.

The more I think about it though, PID may be overkill. I may be able to get away with just "P" (proportional) control based on the rate of rise / fall. The rate of rise, looking at the plots, looks close enough to linear that I think that might work. I'll take the data and run some linear regression analysis on it later, and see what that gives me.

[coppercone2]

do you have the fan in your oven? It makes a big difference, even a small slow fan

BTW the way I wired mine is the fan is connected to its own switch, the modes still control which elements turn on (i.e. broil), the timer is left in place, so the mechanical timer actually disconnects it if you forget. If i have a thermocouple in the middle and I turn the oven fan on after it stabilizes it spikes

[fourfathom]

Here's a plot that shows rate of change (in degrees C per second) and temperature (in degrees C) as my toaster runs the full cycle.  Again, I turn off the heater at 100C , wait 60 sec then turn it back on, off again at 215C, then open the door right after the peak.  I didn't use the cool-down fan for this run.  As you can see, the rate is quite variable.  It takes a long time for the heating elements to come up to full heat or to cool off. 

I'm going to run this again without the "soak" shutdown, and set my off-point at 250C, just to see the behavior.  I'll bet we could model this as a loaded RC (or LC?) low-pass filter.  We've got a voltage/heat source, a heater thermal lag, a "capacitor" (thermal inertia), and a load (thermal leakage to outside ambient).

Again, I'm not seeing the value in using a proportional heater drive.  I do this when doing thermal testing of components and I want to maintain a fairly low temperature in the toaster, but for the reflow even 100% on / 100% off barely gets me to the desired thermal ramp rate.  Using anything less than 100% is only going to slow down the rate of change.  Perhaps if I added insulation a proportional control would make sense.

[mindcrime]

Again, I'm not seeing the value in using a proportional heater drive.  I do this when doing thermal testing of components and I want to maintain a fairly low temperature in the toaster, but for the reflow even 100% on / 100% off barely gets me to the desired thermal ramp rate.  Using anything less than 100% is only going to slow down the rate of change.  Perhaps if I added insulation a proportional control would make sense.

I'm probably mis-using the term "proportional" here. What I mean is just that, since the ramp up rate (with the elements full on) seems to be close to linear, the temperature at time t is directly proportional to t, including the overshoot period after the elements go of, so I can achieve a particular value of temp by doing a simple multiplication of t to tell how long to run the elements. What I'm envisioning would, in effect, be almost identical to what you do, modulo any difference in the constant(s) involved. Maybe you have to run your elements for 100 seconds for the first period, and I have to do 95, or 105, something like that. But the basic idea is the same.

I'm definitely not proposing anything like PWM, or trying to modulate the power to the heating elements in any way other than "on" or "off".

[mindcrime]

do you have the fan in your oven? It makes a big difference, even a small slow fan

There's no fan in this oven by default. I could see adding one if it becomes necessary though.

In fact, I almost certainly will add at least one, to cool the case area where the electronics live. Not yet sure if it will be necessary to add anything to forcibly move air through the cooking chamber or not.

[coppercone2]

I thought there was a fan in the oven, based on your picture.

I see a motor and some kinda vents in the side of the oven in the opening pictures in your thread. What am I looking at?
https://lh3.googleusercontent.com/pw/ACtC-3en77W0POn-RK16h_JZ2_LsB2ruJMBqGtA-JGGH6liVDBJRKC-_dlcBIdCFZGUCJPs9bT6etZf53wocdq4lBrfRc5DzyTUNW0X6xj2Rws_dt5OxKHtBWoktv4rUaSdeQxlRyrjh598n_k2_PZgPNq31=w1244-h933-no?authuser=0

at the bottom, that looks like a circulation motor.

[mindcrime]

I thought there was a fan in the oven, based on your picture.

I see a motor and some kinda vents in the side of the oven in the opening pictures in your thread. What am I looking at?
https://lh3.googleusercontent.com/pw/ACtC-3en77W0POn-RK16h_JZ2_LsB2ruJMBqGtA-JGGH6liVDBJRKC-_dlcBIdCFZGUCJPs9bT6etZf53wocdq4lBrfRc5DzyTUNW0X6xj2Rws_dt5OxKHtBWoktv4rUaSdeQxlRyrjh598n_k2_PZgPNq31=w1244-h933-no?authuser=0

at the bottom, that looks like a circulation motor.

Ah, sorry, I misunderstood you. I thought you were talking about a fan to vent air to the outside, for forcible cooling. Yeah, I guess the fan that circulates air inside the chamber counts as a fan too. :-) I just wasn't even thinking about it.  I wasn't planning to do anything with it, except let it keep it's default behavior, which as far as I know, is to be on whenever the heating elements are on.

I guess I could rewire it to switch independently of the heating elements, if needed. In my head I was thinking more about adding a separate fan if I wound up needing more cooling.

[coppercone2]

Well you are not turning the fan on and off on the SSR are you? Thats why I put its own mechanical switch, for instance if I am preheating parts for soldering, welding, painting, curing epoxy at some random elevated temperature, etc, I keep the fan off. I might be useful to not have a fan going if you are just doing a warming cure of saying potting compound. You get more out of your oven IMO if you have the option to disable the fan, it seems unnecessary for some times, and you can experiment which thermal profile is better. And of course you can experiment to see if its better maybe to run the preheat more aggressively then turn the fan on sometime after to get a rapid temperature spike that you need to match a profile, or to turn it off when you are blowing out the oven during its cool down phase, since you don't really want to be circulating the air in there anymore, you want it to get out.

I think maybe your oven and beans oven are different because one has a fan and one does not, it changes the behavior, I know this for a fact. I thin its more efficent because you have less stratification (bunch of hot air near the top), so it might actually also increase element life when its running real hot because their not bathed in their own hot air. But if I am doing like a 1 hour varnish cure, I don't see the point of running the fan, or if I am heating a part to max before letting it cool down to spray paint.

The other thing I did is I glued (with jb weld) a stainless steel piece of sheet I bent into a small U shape, so that I can put a ceramic thermocouple connector in there, and rest it in the top in the little shelf, so I can disconnect the thermocouple and put a new one on, because then you can just unplug it near the ceiling of the oven and change the thermocouple if you damage it easily without taking it apart . I also cut small noodles out of ceramic tube (from a broken heating element I found in the trash) and glued them into the hole s for running the thermocouple wire to make sure it does not get cut (I made it smooth with a dremel diamond point).

[mindcrime]

Well you are not turning the fan on and off on the SSR are you? Thats why I put its own mechanical switch, for instance if I am preheating parts for soldering, welding, painting, curing epoxy at some random elevated temperature, etc, I keep the fan off. I might be useful to not have a fan going if you are just doing a warming cure of saying potting compound. You get more out of your oven IMO if you have the option to disable the fan, it seems unnecessary for some times, and you can experiment which thermal profile is better.

You make a good point. I might just go ahead and add a separate switch for that fan at some point. I can see how it might be useful for certain applications, now that you mention it.

[coppercone2]

I thought to add a speed controller for the fan too, it should fit in my oversized chassis, but its already pretty weak as it is, and I am not sure how much it will like a controller since its already operating in pretty extreme conditions for a fan, I am not sure about those cheap AC motor speed control circuits and how they do with heat and what the effect on the coils is.

[mindcrime]

I thought to add a speed controller for the fan too, it should fit in my oversized chassis, but its already pretty weak as it is, and I am not sure how much it will like a controller since its already operating in pretty extreme conditions for a fan, I am not sure about those cheap AC motor speed control circuits and how they do with heat and what the effect on the coils is.

I hear ya. For me, I'm probably just being overly paranoid, but given that almost all of my electronics knowledge / experience (to the extent that I have any) involves working with low-voltage DC stuff, I'm reluctant to do much fiddling with the AC mains voltage level stuff in the oven.

I've mostly been trying to treat it all as a "black box" where the only thing I do is use the SSR to turn the power on and off, and everything "downstream" of the SSR says unmodified. The only other thing I'm doing (so far) that involves the AC side, is tapping into the AC cord to connect my step-down transformer which provides the low-voltage DC rails, and adding a rocker switch on the back of the chassis.

[fourfathom]

mindcrime, I finally noticed that your oven has an internal fan, and mine doesn't.  The different construction is probably why our heating and cooling ramps aren't identical.  As for messing with the AC voltage wiring, The only modification I've done to the oven is to drill a tiny hole in the back for the thermocouple lead.  I'm using an aluminum foil-wrap gasket to protect the lead and to seal the air leaks.  I have an external SSR in the middle of a short extension cord that the oven is plugged into.  The SSR, and my controller are all powered via the USB interface to the controller.  My controller has two buttons and a small display which lets me start and stop the reflow cycle, or initiate self-calibration cycles, but I usually run the controller from a PC program that I wrote.

Just for fun, I've been trying to model the thermal behavior of the oven, and I've come pretty close with an electrical equivalent in LTSpice.  I ran some tests with the heater at 10% and 30% duty-cycle to see what the steady-state chamber temperature was for a given heater power, and logged the door-closed cool-down cycle to find the chamber thermal mass (capacitance) and the chamber-to-ambient thermal leakage (resistance).  I also empirically added a second R-C delay to the circuit to model the heating/cooling lag in the heater element.  This gives me my overshoot.  The component values look strange because I've been playing with time-scaling and other normalizations.  Now the scale is 1 second = 1 second, and a heater voltage of 10,000V = 100% duty-cycle.  It comes pretty close to matching my oven, but if I ever want to use the model for anything practical I will need to dial it in a bit more.

[mindcrime]

I have an external SSR in the middle of a short extension cord that the oven is plugged into.  The SSR, and my controller are all powered via the USB interface to the controller. 

It's funny you mention that. I am actually using an SSR wired into an extension cord as well, but I consider that to be "just for the prototyping phase." I plan to eventually mount the SSR and the step-down transformer inside the oven case, just so it will be all nice and self-contained.

Just for fun, I've been trying to model the thermal behavior of the oven, and I've come pretty close with an electrical equivalent in LTSpice.  I ran some tests with the heater at 10% and 30% duty-cycle to see what the steady-state chamber temperature was for a given heater power, and logged the door-closed cool-down cycle to find the chamber thermal mass (capacitance) and the chamber-to-ambient thermal leakage (resistance).  I also empirically added a second R-C delay to the circuit to model the heating/cooling lag in the heater element.  This gives me my overshoot.  The component values look strange because I've been playing with time-scaling and other normalizations.  Now the scale is 1 second = 1 second, and a heater voltage of 10,000V = 100% duty-cycle.  It comes pretty close to matching my oven, but if I ever want to use the model for anything practical I will need to dial it in a bit more.

That's awesome! It would never have occurred to me to model thermal mass as capacitance, and so on. Very clever. I wonder if that's been done before?

[fourfathom]

I am actually using an SSR wired into an extension cord as well, but I consider that to be "just for the prototyping phase."
[...]
It would never have occurred to me to model thermal mass as capacitance, and so on. Very clever. I wonder if that's been done before?

I usually keep my "prototyping phase" lash-ups as long as I don't have to look at them.  Mine is behind and underneath the oven (the oven is standing off the bench, sitting on a couple of red bricks.)

Re: thermal mass as capacitance, I'm sure it's been done before.  We model thermal paths such as "theta J-A" (junction to ambient thermal resistance) as resistance, so thermal mass as capacitance just makes sense.  Hell, I used to model tidal flows in a river as  resistors and capacitors (lumped approximation) , and we sometimes use water tanks as an analogy for capacitors when explaining electricity (voltage = pressure, current = gallons/minute flow rate, etc.)  Sometimes analogy gives you a better feel for something than would a pure mathematical analysis -- at least it does for me.

[mindcrime]

Project Update, 05-28-2021

More (minor) progress. I have the transformer for the low-voltage rails mounted inside the case now.





Up until now, that transformer had its own independent AC mains connection:



So my next step now is to finally start hacking on the AC line coming into the oven, and tee off of that to supply the transformer. I'll also be adding a switch to the mains feed so I can turn everything off easily.

The other "next step" is to take these two boards:



And combine them.

I originally built them separately as I was prototyping select bits of this in a very piecemeal fashion. One board is just the low voltage power supply, which features a bridge rectifier and a couple of linear regulators. The other board is literally just a transistor, a resistor, and some headers. It's just there for level conversion so the  3.3V arduino pin can control the SSR which needs a minimum of 4V for the control side. 

Then I need to mount that combined board, the SSR, the Arduino, and the thermocouple amplifier board, add the switch, and wire everything up.

All of the stuff shown above with the keypad and the LCD will, I think, go in a separate enclosure, which I will mount on top of the oven, or on the side, or something. Once that's done and the software parts are all fixed up, I will have a more or less usable reflow oven (if I am standing there ready to open the door at the right time).  Adding the actuator for the door will come pretty close to last, I think.

I also ordered a piezo buzzer to use for alerting me when a profile run ends, or if any kind of error state (high temperature, etc.) occurs.

[mindcrime]

Aaaand, more progress. I have the SSR mounting taken care of now. It nestles in there right below the transformer.









Getting closer and closer to having this thing built! Still plenty of work to do, but progress is evident. 

[coppercone2]

did you measure temperature with the housing on to see what temperature that stuff in there will operate at?

For my oven I left the side wall in tact save for a gland/strain relief (separate one for thermocouple) and put the electronics in a big steel electrical box mounted to the side, with a grate on it, to ensure the electronics will not get hot. I have a feeling that area will get really toasty. The failure rate of electronics is proportional to heat so when you have stuff in there tight, it will have an increased chance of (dangerous) failures, and shorter life. Maybe putting a grate on the side will help vent it but that area gets toasty. Before you do more work, I suggest putting the lid on and measuring the temperature in that cavity. And, don't forget fuses now that you have added more complex electronics that can fail short.

The only caviat is that you need good grounding if you add a box to it for safety reasons, you don't want the metal box you add to be left floating.

You might be really disappointed by the temperature you will get in that cavity now that you put work into it.

When you measure temperature, run it for like 30 min to see what it gets to, you want to keep options for use open because having a good temperature controlled oven like I said before is a good asset in the electronics lab and it would be a shame to limit its capabilities to save on a steel box (some where between free and $20). you put alot of work into it so its best to make sure you get your value without surprises on operating limits.

[mindcrime]

did you measure temperature with the housing on to see what temperature that stuff in there will operate at?

Not yet, but that's in the plans as soon as I get the SSR, the transformer, and the switch mounted, and the AC side wiring done. I'm already committed to having a box mounted on the side/top to hold the keypad and display, so yeah, I've considered that it might make sense for most of the other electronics to live there as well. I *think* I can get away with the SSR and the transformer where they are, but I do plan to do testing around that very point. And the good thing is, given the mounting holes I drilled, I can easily just flip both of those components to live outside the case as well.

Before you do more work, I suggest putting the lid on and measuring the temperature in that cavity.

You might be really disappointed by the temperature you will get in that cavity now that you put work into it.

Yep, definitely going to be doing that. I'm also planning to measure that both with and without additional insulation in the inner chamber to see how that affects things. I've also considered that I might add an exhaust fan to move air through that cavity if necessary.

[coppercone2]

if you add an exhaust fan without insulation its going to cool the oven and make a thermal gradient because its like putting a big flat heat exchanger on the side of  the oven wall, minor, but the wider the PCB the more an effect it will have

[mindcrime]

if you add an exhaust fan without insulation its going to cool the oven and make a thermal gradient because its like putting a big flat heat exchanger on the side of  the oven wall, minor, but the wider the PCB the more an effect it will have

Right now I'm leaning towards the idea that I will be adding insulation. I haven't done it yet, but I was chatting with my buddy who built a similar setup, and he made a good point about that. That being, even if the oven gets up to temp with no problem without extra insulation, having the extra insulation reflecting the IR around inside the chamber should help with creating a more even temperature distribution.

I doubt I'll ever be soldering boards big enough for that to matter, but I'm kinda leaning that way. It may also help reduce some heat transfer into that side chamber inside the case that we were just talking about. The downside, if there is any, may be some reduction in the cooling rate on the cool-down phase. But since I'll be opening the door anyway, I don't think that will be a big issue.

That said, "test all the things". I'm big on empiricism and actually measuring and seeing what happens. I just finished up a lot of the work that needs to happen inside the oven case itself, so very soon now I'll be ready to put the outer cover back on, and start doing more temperature measurements and testing things out. 

[mindcrime]

Project Update, 05-29-2021

I've finished up a big chunk of the work that has to happen inside the oven case. OK, I suppose that technically nothing has to happen inside the case, as you can do this kind of conversion with keeping everything outside. But in this case, I chose to package some of the bits inside the existing oven shell. How that works out remains to be seen...

Anyway, I put the rocker switch in, and re-did the AC mains feed so that it goes through the rocker switch, and then after the switch tees off with one branch going to the SSR (for the heating elements) and one branch going to the transformer that will power the low voltage stuff.  All that really remains to be done in here is connect the wire coming off the output side of the SSR back to the wire going to the heating elements. I left it disconnected to do some initial testing, just to make sure I had everything else wired up correctly, and that the transformer worked, etc. So far everything looks good.



Switch now mounted alongside the other components.



Another view.



The switch, seen from outside.



Hard to see in this picture, but it lights up when switched "on"



And, as expected, we get our 12VAC from the transformer when the box is powered up.



This connection right here is one of the last bits remaining in here. That will join the SSR output to the wire that runs through the existing oven controls, and ultimately to the heating elements and what-not. The SSR datasheet recommends a fast-blowing fuse in this circuit, so I have fuse-holder I need to wire in.

[coppercone2]

just, keep this in mind.
https://www.digikey.com/en/products/detail/bud-industries/JB-3954-KO/2674114?utm_adgroup=Boxes&utm_source=google&utm_medium=cpc&utm_campaign=Shopping_Product_Boxes%2C%20Enclosures%2C%20Racks&utm_term=&utm_content=Boxes&gclid=CjwKCAjwzMeFBhBwEiwAzwS8zA7IlaWvJAmPnVkRLjdH3Tx2dZPwq3WUBJkOaCig-Pf3czLVLQQybhoCxVYQAvD_BwE

it makes your life alot easier and you just need to cut or buy 1 piece of metal for the top, the only hard part is making the holes for the display etc. you put tape on the knockout and pour epoxy on it to seal it up if you want then take the tape off

[fourfathom]

I've seen these toaster-oven conversions with the electronics inside the case, so I guess it can be done, but I went with the external Bud Box solution. (I like that epoxy display window idea!)  The only modification to the toaster was to drill a hole for the thermocouple cable, everything else is external.

[coppercone2]

I think I read one mod where the control electronics had the wrong temp because of the heat, did dave jones not have this problem when he left his controller on top of the oven also?

[mindcrime]

Today has been a long day, but finally some significant progress.



The SSR line to the oven electronics is connected now. Yay!



Not the neatest looking job, and I still have some insulating sleeve material I may need to put around some of this wiring, but we'll see.



Two key things come outside - the low voltage (12VAC) rail, and the INPUT side of the SSR. With those two things and the thermocouple, I can have all the "real electronics" packaged up in a box that mounts to the top or side or whatever.



Yes that is ugly and hacky - and more to the point, TEMPORARY. I don't routinely leave wires rubbing on semi-sharp edges. This is just so I can do some testing with the oven basically assembled again. I'll do holes with grommets and wire clamps and/or whatever before calling this "done done".



Low voltage rail working - again. This cost me SO much time. I had the low voltage stuff working earlier (see above) but then it quit working for some mysterious reason after I finished wiring up the SSR and everything. In the end, I had out-smarted myself. I used some (shitty) pluggable connectors to connect the wires to the transformer, thinking "If I ever need to replace this thing, it's better if I can just unplug it."  Apparently the connectors were tarnished, or made out of crappy material, or both, as it quit connecting at some point when I was moving stuff around. Took forever buzzing around with the continuity tester and what-not to finally find the fault. Once I did, I ripped all that connector crap out, and just spliced the wires directly together, soldered the  joint, sealed it with heat-shrink tubing and called it done.





All buttoned up and back in one piece. Now for more thermal testing, evaluating use of additional insulation, checking the temperature in that side chamber, etc., etc, etc. Given that this is a "3 day weekend" here in the States, I may actually be able to do some test soldering before the "weekend" is over. That is, if I have any solder paste here that isn't too old to be usable.

[coppercone2]

put a few layers of heat shrink over the wire going through the vent hole, the teflon kind if you have it

also for deburring the vent, there is NO better tool then a abrasive rubber point for a dremel, they wear quick but your vents will be like, ultra smooth

https://www.amazon.com/Dremel-463-Rubber-Polishing-Point/dp/B00004UDHR

get the black ones if you can find them for that


also, this is the video where dave jones has problems with his reflow oven overheating the controller


if I am doing a wire route without a gland (you should actually use a gland, like the ones they sell for electrical boxes at home depot, you drill a hole , put the wire through a peice of silicone tubing and clamp it if you don't want to buy proper glands, they are nice and metal), I use these for deburring, they will leave an amazingly smooth surface for wire, beware punched vent holes, they are often sharp.

https://www.ebay.com/itm/322139737579?epid=2164364418&hash=item4b01064deb:g:yQsAAOSwxt5fA28y


For my oven I used a $50 panasonic SSR, you want to treat the cheap ones real well, and downrate to ~50% of their real rating, some people going down to 25% on the forum


But anyway, those black points won't get too much deburred unless you are real careful, but they are amazingly easy to use and fast and convenient, so its good for prototyping at least, unless you wanna get out 5 pieces of different grit sand paper lol, it stays professional

[mindcrime]

also for deburring the vent, there is NO better tool then a abrasive rubber point for a dremel, they wear quick but your vents will be like, ultra smooth

https://www.amazon.com/Dremel-463-Rubber-Polishing-Point/dp/B00004UDHR

Interesting. Never seen one of these before. Thanks for the pointer, I just ordered one. Funny that would come up in this moment, as I got a lot of use out of my Dremel tool earlier today, working on this thing (mostly to do with mounting that switch). I don't use the Dremel all that often, but when you need  it man oh man, is it handy.

also, this is the video where dave jones has problems with his reflow oven overheating the controller

Yep, I've seen that one. Probably wouldn't hurt to go back through it again though...

For my oven I used a $50 panasonic SSR, you want to treat the cheap ones real well, and downrate to ~50% of their real rating, some people going down to 25% on the forum

I went with an Autonics SR1  SSR. Not the cheapest ,not the most expensive. It's rated at about twice the expected current consumption of the device, so I think I'll be OK there.

[coppercone2]

crap, get the black one off ebay if you want to debur, that one will also do it but its finer and wears more, their supposed to be sequential, I think just the black one is enough, when you follow up the black one with the other ones it feels like smooth wire

if you have really good tool control they last a longer time, but they are somewhat expensive and wear quick compared to other abraisve types.

oh yeah, beware, the ebay one needs a smaller collet, so only do it if you got the dremel collets that are smaller size.

a worthy investment because that is a stupid thing that can really hurt you, a wire shorting to a chassis

ALso, I only used mine for stainless steel, they might be alot longer life on other materials. just don't press too hard. its a recent acquisition (last week, which I had them 10 years ago).

with the blue one I expect if you hit it with some rough sand paper haphazardly before you debur it will wear less. the problem is you get sharpish stuff thats painted, the paint makes it feel smooth, but there is potentially a knife edge under neath.

I also suspect their going to be very good for stripping thicker magnet wire, cleaning corrosion around ground points in old equipment, the ultra fine ones might be good for cleaning contacts too, but I prefer radial nylon abrasive brushes for those, since their more delicate, but anyway its a damn good tool so long you don't save your budget too much thinking about when to use it.


Right, they are also the PACE soldering recommended way of cleaning charred materials, silkscreen, corrosion, etc off circuit boards you are repairing, all the pace stuff is either ruberized or leatherized abrasive (leather dust mixed with abrasive and hydraulic glue or rubber dust mixed with abrasive and heated).  and you can clean up a ring terminal

[beanflying]

I think I read one mod where the control electronics had the wrong temp because of the heat, did dave jones not have this problem when he left his controller on top of the oven also?

If you drop the controller on top then sure bad idea on the side and in particular lower down on the side of the oven it won't be much of an issue in particular if you thermally insulate it from the oven either by material or forced airflow over the board. Part of the reason for this is if your temperature sensing uses cold junction compensation and the ambient where the board sits ramps along with the actual oven it will throw your sensing off. Before you get to the issues of Electronics impacting the electronics from general heat issues.

[mindcrime]

oh yeah, beware, the ebay one needs a smaller collet, so only do it if you got the dremel collets that are smaller size.

Hmm... not sure what size collet mine has. It's not an actual Dremel brand tool, it's the Craftsman version. Not sure if I even have the manual or anything around here. Maybe if I can find the model number on it I can Google it up.

Anyway, no big deal. I have the one from Amazon coming, so that'll be handy enough in the short-term.

a worthy investment because that is a stupid thing that can really hurt you, a wire shorting to a chassis

True. Although in any meaningful context I would never leave a wire running unprotected through a panel without using a rubber grommet at a minimum, and more likely a purpose built cable gland of some sort.

[coppercone2]

if you do it for long enough you eventually forget something, imo

[mindcrime]

Project Update 05-31-2021

Did some more ramp-up / ramp-down thermal testing just now, to see how things look with the outer cover back on. At first blush, it actually doesn't appear to have made a huge difference, but I need to spend some more time crunching the data to be sure. Note that this plot is misleading if compared to the previous ones, because the scale of the x-axis is different.

Briefly, though, it took 182 seconds to get to 250° C with the cover on, as opposed to 217 seconds without the cover. Note that this isn't a very scientific test as I am not controlling for the ambient temperature in the room, etc. But it does suggest that the outer cover helps hold heat in a little more effectively, which one would expect. Also, with the outer cover on, there was a little bit more overshoot past the target 250° point.  With the cover, the temp went up to 261°, whereas it peaked at 253° without the cover. I would say that is also totally as expected given better trapping of heat inside the inner chamber.

Code: [Select]

0,32.07 # Turning OVEN on
2,32.02
4,32.00
6,32.14
8,32.19
10,32.27
12,32.58
14,32.73
16,33.04
18,33.50
20,34.02
22,34.76
24,35.52
26,36.57
28,37.66
30,38.92
32,40.30
34,41.87
36,43.73
38,45.73
40,47.59
42,49.76
44,52.20
46,54.50
48,57.03
50,59.53
52,62.30
54,65.22
56,68.00
58,70.88
60,73.99
62,77.14
64,80.24
66,83.70
68,86.94
70,90.18
72,93.50
74,96.86
76,100.28
78,103.61
80,107.03
82,110.55
84,113.97
86,117.37
88,120.83
90,124.18
92,127.52
94,130.96
96,134.51
98,137.98
100,141.34
102,144.68
104,147.96
106,151.04
108,154.31
110,157.45
112,160.57
114,163.62
116,166.90
118,170.00
120,173.01
122,175.91
124,178.99
126,181.87
128,184.95
130,187.66
132,190.41
134,193.12
136,195.82
138,198.71
140,201.43
142,203.96
144,206.62
146,209.16
148,211.86
150,214.37
152,216.88
154,219.20
156,221.53
158,224.07
160,226.59
162,229.07
164,231.50
166,233.75
168,236.12
170,238.33
172,240.43
174,242.69
176,244.88
178,246.95
180,249.17 # Turning OVEN off
182,251.67
184,253.84
186,255.20
188,256.70
190,257.71
192,258.92
194,260.00
196,260.85
198,261.16
200,261.45
202,261.39
204,260.24
206,257.87
208,255.59
210,252.52
213,249.80
215,247.70
217,245.39
219,243.34
221,241.15
223,239.01
225,237.31
227,235.59
229,234.06
231,232.01
233,230.41
235,228.35
237,226.08
239,224.27
[snip]
823,39.70
825,39.62
827,39.50
829,39.41



Next up, do some measurements of the temperature in the side chamber. And I'll probably try adding a layer of insulation inside the core chamber and then re-test everything to see just how much of an impact that has.

[mindcrime]

Just for the sake of comparison, here's a standard Kester reflow profile for leaded solder. Not sure if I'll be using Kester solder paste primarily, but this is probably fairly representative. Looking at this, I don't think that matching a profile like this relatively closely is going to be too much of a challenge.

[coppercone2]

Don't worry too much about room temperature with such a high temperature instrument, a livable area won't see anything past 15 above room temp and thats really bad, and you clearly have a very big difference because of the cover. the insulation will change it tons more

[mindcrime]

Up next, take all of this stuff, along with the keypad and the LCD display, collapse/combine things as necessary, and package it all into a proper enclosure. And route those wires properly that are stuck in those ventilation slots right now.

[coppercone2]

you can mount the heatsink on a bracket made out of bent metal and put the circuit boards up on hex standoffs if you have the room

for wiring if you want it nicer you can bent brackets and put zip tie holders on them.

[mindcrime]

OK, more testing results.

Before adding any insulation or doing anything, I did a 6 minute "full on" test to see how warm that side chamber was getting. As expected, it was a bit toasty. It made it up to a whopping 155° C. Now I would never do 6 minutes of "full on" for soldering anyway, but still, that's clearly not a good position.

Soo... went in and made a bunch of heat shields out of pieces of aluminum flashing, wrapped in the same insulation I bought to use inside the main oven chamber. Formed and twisted those around to make an isolated pocket near that back wall, where the SSR and the transformer are mounted.  Also added insulated sheathing around some of the new wiring I added, and the fuse holder. Added a layer of insulation to the inside wall of the outer cover, on top and on the left hand side (*not* the right hand side, since I very explicitly don't want to trap extra heat over there!).

Put the cover back on and did another 6 minute "full on" test. Now the temperature in the pocket where the SSR and transformer live stays down to a much more manageable 76° C. It's still a little bit toasty, but that's also an unrealistic scenario for soldering. And I still haven't added a layer of insulation on the inside walls of the inner cooking chamber, which should help even more.  So right now I'm pretty content with this situation in terms of using the oven for soldering. If / when the need to use it for some other use cases arises, I can look at adding a fan to pull air through the SSR/transformer chamber. With all the insulation that's either already there, or will be added, and assuming it's a small fan, I don't expect that will mess with the temperature gradient in the inner chamber enough to matter. 

No pictures this time, as I forgot to take any before putting the cover back on. Shame, as I was quite pleased with how those heat shields came out. 

[fourfathom]

While I haven't added insulation to my oven, I do think that if you add it to the inside of your chamber this will accelerate the cool-down phase, and this is a good thing.  My oven is a bit slow on the cool-down, even with the door open (fanless), so using insulation to reduce the thermal mass inside the chamber can only help.

[coppercone2]

well I think its a bit of a trade off here, if you put it on the inside of the oven you loose oven space but you insulate the ovens thermal mass, but if you put it between the walls you maintain space but you still have the inside structure of the oven so its not as good (the air space in there is a somewhat decent insulator so it won't be magical.

What insulation is good for being thin, and clean? I thought about this but I am worried about dust contamination, particularly with the fan.

And the bottom of the oven typically will require the insulation. And I also wonder, what does it do for the weld joints that like to break in the oven? If they are insulated inside of the wall, won't they heat up more and distort more? The bottom and back wall IIRC are not doubled walled, but the side and top are. And if you insulate inside sidewall I think you mess with the thermostat, I don't think the temperature corrosponds well so if you want to maintain the 'dumb' features of your oven as a safety it will be bypassed.

I think insulating the interior of the oven will be the best. I thought graphene sheets but  I heard they are super messy, so you how to seal the seams? silicone? And if you insulate the inside not the wall, should you add some vents to the inner wall to allow the crimps etc to cool down a little? But if they run at a lower temp it might be better to leave it alone. lots of probing to test this IMO

i would test this stuff but taking the oven apart is such a hassle I don't want to lol, if I keep taking off that lid something is gonna break.

the temperature you achieved in the side chamber is a game changer, so long the crimps or welds are not under higher temperature

[mindcrime]

OK, just got done adding a bunch of insulation to the inner chamber, and doing another side-chamber test for 6 minutes.







Not a perfect job, but it makes a difference. I ran the 6-minute "full on" test again and now the side chamber temperature peaks at 64° C. That's down to within the specified range for both the SSR and the transformer (both list peak temperatures of 70° C). And I don't expect to see even the 64° during a typical soldering run. So right now I think I'm in pretty good shape with regards to that stuff.

Now I'll be really curious to see what the temperature curve inside the oven itself looks like. I'm probably going to kick off another test run of that here in a few minutes.
 

[mindcrime]

What insulation is good for being thin, and clean? I thought about this but I am worried about dust contamination, particularly with the fan.

Time will tell how "good" it is I guess, but here's the insulation I went with:

https://www.amazon.com/gp/product/B08GG22QHC/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1

the temperature you achieved in the side chamber is a game changer, so long the crimps or welds are not under higher temperature

It's even better now. On my last 6 minute run, the temperature in the side chamber peaked at a comparatively balmy 64° C.

[mindcrime]

OK, here are some more results. With the insulation inside the main chamber, I did one of my "run up to 250° and then shut off" tests. It took about 230 seconds for the oven to reach 250° this time, compared to about 181 seconds from the last run before adding the insulation.

"Wait", you're saying, "why did it take longer to get up to temp with the insulation as opposed to without it?"  Well, I can't be 100% sure, but the tests weren't identical. For one, the earlier run had the inner chamber at 32° when the run started, while the one just now had it at about 26°. I may also have had the thermocouple positioned slightly differently, making it not an "apples to apples" test. There are probably also other variables I'm not considering.

OTOH, there was noticeably less overshoot this time, which is good.

All in all, I'm fairly satisfied with this. I still need to write code to implement an actual reflow profile, but assuming I have the coding skill to do that (not a guarantee, but I'm a better coder than I am electronics engineer, or thermal engineer) then I think this is going to work out quite well.


Edit: looking at the data, on this last run it took ~30 seconds to go from 26° to 32° degrees. That alone represents the bulk of the delta between the two runs. I think that 181 second run was one I did where I didn't let the oven finish cooling down fully from a previous run, so it's a little bit misleading.

[mindcrime]

An early stab at prototyping what the control box might look like:

[mindcrime]

OK, latest results:

1. Added more insulation to the left hand side panel of the inner chamber. Did a "up to 250° C" ramp-up / ramp-down test from a cold start and found that it took ~230 seconds to reach 250°. That is consistent with my earlier observations when doing it with the oven cold. By and large, adding insulation to the inner walls of the cooking chamber did not seem to have a ton of impact on the "time to reach 250°" performance, but it did have a noticeable impact on keeping that side chamber cooler. So net-net, adding insulation there seems to be a win and a generally desirable thing.

2. Suspecting that the glass panel on the front door was a significant source of heat loss, but not wanting to permanently block my view into the oven, I made two slip-in heat shields out of two of those pieces of aluminum flashing and some of the insulation. The flashing pieces coincidentally turned out to be exactly the right height, so no cutting was necessary. And there's a little ridge near the bottom of the door that the heat shield will catch on, which helps keep it in place while shutting the door. Of course I could bodge in some Kapton tape to hold them in place if I wanted to.



These pieces just lie inside the door frame and are held in place by the door itself.



Reflecty stuff, cool.



The way they lean up against the frame. When the door is shut, they're locked into place well enough.



View from outside with the shields in place, and the door closed.

Did another 250° ramp-up / ramp-down test from cold start, and found that adding those brought the "time to 250°" performance down to 196 seconds. So yeah, it appears that the glass front is a major source of heat loss. Closing down that channel even partially helps by a decent amount.

Now to finish up that control box and get some proper software written for this thing.

On the software side, here's what I think I'm going to try for a first, "strawman" stab at this. Instead of dealing with PID and complicated algorithms, I'm going to take the data from one of my test runs, run linear regression on the side of the curve up to 250°, and use the slope as an approximation that's good enough to use heuristically. Then I'll do something similar to what user @fourfathom was doing, where I'll just rely on timing for the various states, based on the expected change in temp over time. I'm just going to hard-code the timings into my control program for a trial run, and test that approach and see how close I can get to matching a published "official" soldering profile.

I also just ordered a few more of those SOIC-14 to DIP adapter boards and 30 more NE556 timer chips in SOIC-14 format, along with a fresh tube of Kester 63/37 solder paste, so I can start experimenting on actual boards soon. 

[fourfathom]

Then I'll do something similar to what user @fourfathom was doing, where I'll just rely on timing for the various states, based on the expected change in temp over time. I'm just going to hard-code the timings into my control program for a trial run, and test that approach and see how close I can get to matching a published "official" soldering profile.

Looks good.  Have you done any door-open cool-down measurements with the new insulation?

You probably know this, but my method is temperature threshold-triggered timing, not just blind timing.  The ambient and starting chamber temperature still have some effect on the heating curves, but with the temperature thresholds the results are reasonably accurate.

[mindcrime]

Then I'll do something similar to what user @fourfathom was doing, where I'll just rely on timing for the various states, based on the expected change in temp over time. I'm just going to hard-code the timings into my control program for a trial run, and test that approach and see how close I can get to matching a published "official" soldering profile.

Looks good.  Have you done any door-open cool-down measurements with the new insulation?

You probably know this, but my method is temperature threshold-triggered timing, not just blind timing.  The ambient and starting chamber temperature still have some effect on the heating curves, but with the temperature thresholds the results are reasonably accurate.

Not sure if I realized that earlier or not, but that's good to know. I plan to try the dumbest possible approach first just to see what happens, and then gradually add complexity as needed to get a good track against the desired profile. If we're talking about the same thing, then "temperature threshold-triggered timing" sounds like what I'm guessing with be the best combination of "simplest thing that could possibly work" AND "achieves reasonably good compliance with the desired profile". 

[fourfathom]

Not sure if I realized that earlier or not, but that's good to know. I plan to try the dumbest possible approach first just to see what happens, and then gradually add complexity as needed to get a good track against the desired profile. If we're talking about the same thing, then "temperature threshold-triggered timing" sounds like what I'm guessing with be the best combination of "simplest thing that could possibly work" AND "achieves reasonably good compliance with the desired profile". 

Yeah, I mentioned this a couple of times, but probably not clearly.  I have three  temperature trigger points:
* First at 100 deg (start of soak).  When the oven hits this I turn the heater off for 60 seconds, then back on.
* Second  at about 215 degrees (set during calibration runs).  I turn the heat off at this temperature, and if it's going as planned the chamber temperature continues to rise until it hits my target of 235 deg.
* Third when the temperature begins to fall (I think by one degree).  I buzz the buzzer and open the door.  I could probably trigger this when the temperature hits the target *or* starts to fall without quite making it to the target -- that would speed up the cooldown by a few seconds.

So, I basically press "Start" and wait for the buzzer.

My post with the explanation and some plots:
https://www.eevblog.com/forum/projects/finally-starting-on-this-convection-oven-gt-reflow-oven-conversion-project/msg3573697/#msg3573697

[mindcrime]

Yeah, I mentioned this a couple of times, but probably not clearly.  I have three  temperature trigger points:

I don't think there was any problem with you not being clear enough... it's more that there has been a lot of information shared in this thread over the last couple of weeks, and I don't have all the details of everything that was said stored perfectly in memory. 

My post with the explanation and some plots:
https://www.eevblog.com/forum/projects/finally-starting-on-this-convection-oven-gt-reflow-oven-conversion-project/msg3573697/#msg3573697

Yeah, I remember that now. I'm definitely planning to consult that as a reference as I start getting serious about implementing the profile logic.

[mindcrime]

Project Update 06-04-2021

Earlier today I made my first test run with the software attempting to do something that at least roughly approximates the "Kester Standard Profile" as seen here. And while the results are far from perfect, you can start to see the rough outlines of how this can be molded to match their curve.

In the end, I decided not to bother with hand-coding the timings, and do something closer to what @fourfathom was talking about. I may not have done it exactly the same way, but I think the general principle was about the same. Basically I took the Kester profile, worked out the max time and max temp for a given phase, and have the code treat each phase as ended when either the time or the temperature exceeds the boundaries of that phase. For the SOAK phase, since the elements have been turned off at the end of PREHEAT, I'm relying on thermal inertia to continue to carry us up in temperature. That works, but I think I need to stop PREHEAT a few degrees earlier than I do. As it stands, my SOAK phase winds up being really short.

Also, ignore the cool-down phase of the graph, basically. I accidentally moved the test board with the thermocouple a lot when I opened the door and the whole thing fell out of the oven, and I hand to fumble around a few seconds to find something to use to pick it up and put it back.

Anyway, here's a chart, and the raw data if anyone is interested in that sort of thing.

[ Specified attachment is not available ]
 kester_trial2.png

[mindcrime]

Here's another run of that same profile code, but without the fumble on the cooldown side.

 temp_data_oven_06_04_2021_kester_trial_3_with_comments.txt (2.42 kB - downloaded 42 times.)

And a run that tweaks the break between PREHEAT and SOAK down a few degrees. Now the SOAK phase is a little longer and this looks pretty close to what I need, except thermal inertia is now not enough to keep the temp up throughout the SOAK phase. But I could modulate the heating elements a little bit in this phase and I think I could get this very close to "just right".

More experimenting to do...


 temp_data_oven_06_04_2021_kester_trial_4_with_comments.txt (2.43 kB - downloaded 32 times.)

[fourfathom]

For the soak phase at what temperature did you shut off the heater?  How long after that did the chamber temperature start to fall?  As you zero in on this, remember that the temperature won't start climbing again the instant you turn the heater back on -- there is a delay as the heating elements warm up.

It does look like a bit of duty-cycle control on the heater would help you during the soak phase.  I have a duty-cycle option in my oven controller, although I don't use it for reflow.  My duty-cycle technique uses a one-second interval, with the heat ON or OFF one second at a time.  I have a "Bresenham" algorithm (quite simple, really) that keeps the on/off cycle spacing as fast as practical.  For example, a 30% duty-cycle results in a repeating on/off (1/0) sequence of "0010010001", rather than "0000000111". The thermal inertia of the system is enough that this probably makes no practical difference, but I have a thing for Bresenham, having used it a lot in frequency synthesis and other problems.  I'm using the 1-second rate since I don't want to stress my SSR more than necessary.

[mindcrime]

One more try. This graph doesn't necessarily look real pretty, and visually it's different from the Kester profile, although part of that is a scale mismatch. But as best as I can tell, strictly speaking, this would be compliant with their constraints (or very close) even if it doesn't track the ideal graph perfectly. And of course there's plenty of room to continue tweaking and improving the algorithm. I think though, if I stuck a board in the oven and ran this, I'd probably get a usable board out of it.

I would test that theory, but the only pre-made boards I have handy are some SOIC-16 to DIP adapter boards, and I don't have any SOIC-16 parts here, that I can find. For the most part, the only SMD parts I have around are ones I ordered by mistake when I wasn't paying attention and clicked the wrong part number or whatever. I do have some TSSOP-16 shift registers here, but that doesn't help.

Oh well... I have purposely ordered SOIC-14 boards and chips just to use for testing this oven, and they will probably be here Monday. So I can keep tweaking this software over the weekend, and maybe test some boards early next week.

 temp_data_oven_06_04_2021_kester_trial_4.txt (2.25 kB - downloaded 35 times.)

[mindcrime]

For the soak phase at what temperature did you shut off the heater?  How long after that did the chamber temperature start to fall?  As you zero in on this, remember that the temperature won't start climbing again the instant you turn the heater back on -- there is a delay as the heating elements warm up.

It does look like a bit of duty-cycle control on the heater would help you during the soak phase.  I have a duty-cycle option in my oven controller, although I don't use it for reflow.  My duty-cycle technique uses a one-second interval, with the heat ON or OFF one second at a time. 

This most recent run used 150 as the trigger point to run the heater off at the end of PREHEAT. The one before that was 147, IIRC. The big change this last time was exactly to add some duty-cycle control. It's a dumb algorithm, but basically I capture the temp each cycle and store it in a "lastTemp" variable. During the SOAK phase, if the temperature ever drops compared to lastTemp, I give it a 5 second nudge of heat.
That has gotten me a little closer to where I want it, but still plenty of room to tune and experiment.

Code: [Select]

116,145.83
118,149.03
120,151.84
SOAK: Turning oven OFF
122,154.62
124,157.16
126,159.62
128,161.96
130,163.93
132,165.64
134,167.30
136,168.76
138,170.00
140,171.10
142,171.94
144,172.79
146,173.45
148,174.10
150,174.65
152,175.12
154,175.45
156,175.87
158,176.11
160,176.43
162,176.63
164,176.70
166,176.74
168,176.73
SOAK: Turning oven ON
SOAK: Turning oven OFF
175,175.05
SOAK: Turning oven ON
SOAK: Turning oven OFF
182,174.84
SOAK: Turning oven ON
SOAK: Turning oven OFF
189,175.41
191,175.83
193,176.37
195,177.06
197,177.64
199,178.23
REFLOW: Turning oven ON
201,178.57
203,178.77


I have a "Bresenham" algorithm (quite simple, really) that keeps the on/off cycle spacing as fast as practical.  For example, a 30% duty-cycle results in a repeating on/off (1/0) sequence of "0010010001", rather than "0000000111". The thermal inertia of the system is enough that this probably makes no practical difference, but I have a thing for Bresenham, having used it a lot in frequency synthesis and other problems.  I'm using the 1-second rate since I don't want to stress my SSR more than necessary.

Huh. Interesting. I'm not familiar with Bresenham algorithm... I'll have to go read up on this.

[coppercone2]

i use a fuzzy logic 16 zone controller, I did not want to deal with all that programming and possibly EMI and stuff inside of a toaster oven

[I_Saldana]

You lot are all doing it wrong !!!

Turning reflow ovens into toaster ovens should be the essence of this recurring theme.



tsss. *smh*

[coppercone2]

I almost posted this yesterday, but the problem is I only have 1 ssr on my oven. I could require it for 2ssr to make that. Possibly worth doing because the SSR is $50 and its 2 hours work instead of 400$ for a toaster

it would need a bit of brazed brass or stainless tubing leading into the oven, but I don't know how much I want to mix bread an PCB residues. probobly a bad idea

[mindcrime]

OK, time for some real testing! Time to bake boards!!

My first effort...





... was pretty abyssmal. 

That's OK though. The oven did it's part just fine, and it looks like I just put WAY too much solder paste on the pads. Let's try again:





Still a couple of bridged pins there, but I did a better job of controlling how much paste I laid down on the pad. Sadly I'm doing this by hand with just a syringe, as I don't have any stencils for these little breakout boards. I could probably do a better job as well if I pulled out my actual microscope instead of just trying to do it with a simple magnifying glass.

Still, I think once I get my technique down a little better and get a better feel for the correct amount of paste, I'll have no problem producing usable boards using these SOIC components. Going to anything smaller than that would probably be nigh on impossible without using an actual stencil, but that's OK. If I ever send out to have boards fabbed, I'll get a stencil if I'm using any very small form-factor parts. And even if I mill a board at home on the CNC mill, I could probably mill out an associated stencil as well. Maybe not out of stainless steel, mind you,  but at least something to get the paste on the board.

[mindcrime]

This one came out looking OK. The initial reflow job left one solder bridge, but I was able to go in and clean that up by hand. I think the overall process netted what would be a usable board, if I actually needed this for something. Now I just  need to keep practicing and really nail getting the exact required amount of solder on the pad before placing the part.

[fourfathom]

For my complicated boards I use a stencil, but for one-off simple stuff I use a toothpick or small wire to transfer solder paste to the pads.  I can't use the syringe that came with my solder paste, the needle is too large to dispense small-enough drops of paste.  Perhaps a smaller-diameter needle would work, but the one I have already takes too much finger pressure to operate easily.  When hand-pasting the 0.5mm QFN packages, I essentially drag a thin line of paste across all the pads on a side, and the melting solder wicks to the pads and leaves a clean gap in-between.  It's extremely seldom that I have a short or open.

Bur a stencil is really the way to go for any significant board.

[coppercone2]

I just cured another varnished buzzy HP transformer in mine

[mindcrime]

For my complicated boards I use a stencil, but for one-off simple stuff I use a toothpick or small wire to transfer solder paste to the pads.  I can't use the syringe that came with my solder paste, the needle is too large to dispense small-enough drops of paste.  Perhaps a smaller-diameter needle would work, but the one I have already takes too much finger pressure to operate easily. 

Yeah, I know what you mean. It's hard to be precise with the syringe, because you have to apply so much pressure just to get the solder out. 

When hand-pasting the 0.5mm QFN packages, I essentially drag a thin line of paste across all the pads on a side, and the melting solder wicks to the pads and leaves a clean gap in-between.  It's extremely seldom that I have a short or open.

I had thought about trying the "lay a line across the row of pads" approach. When you do that, do you just put the line on and then place the component? Or is it necessary to take a razor blade or something thin and divide the line between the pads?

I may give that a try tonight after work. That or try the approach of just globbing some solder out on a scrap piece of board and then transfer it in small dabs with a piece of wire, or something along those lines, as you mentioned above.

Bur a stencil is really the way to go for any significant board.

No doubt! 

[fourfathom]

I had thought about trying the "lay a line across the row of pads" approach. When you do that, do you just put the line on and then place the component? Or is it necessary to take a razor blade or something thin and divide the line between the pads?

I may give that a try tonight after work. That or try the approach of just globbing some solder out on a scrap piece of board and then transfer it in small dabs with a piece of wire, or something along those lines, as you mentioned above.

I use the wire or toothpick to lay/drag the line of paste across the pads.  The syringe I have puts out too much for that approach (perhaps for larger geometry pads it would be OK?).  No need to clear the pad gaps, the solder wicks into the pin/pad junction and automatically clears from the inter-pad gap -- as long as you don't use too much paste.  Sorry, I don't have any descriptions better that "enough" and "not too much", but I've just been eyeballing it and it doesn't take much solder to make a good junction when there is close pad/pin alignment.  Getting the paste to stick to the wire / toothpick / pad seems to be a function of paste temperature -- too cold and it just doesn't stick, too warm and it is too runny.  "Comfortably cool room temperature" seems about right.

[mindcrime]

Project Update 06-09-2021

Got off work today and was feeling pretty lazy, so I didn't make much progress here. What I did do was finally take some baby steps towards getting this "control unit" thing packaged up properly. Specifically I worked out a way to mount the LCD to the box, using some small "L"-brackets.

It took a little  massaging with the dremel tool and a grinding wheel, but it all fits together reasonably nicely now.









I'm torn on whether or not I feel like putting in the effort to cut a rectangle in the top lid of this thing, that exactly fits around that inner frame of the keypad, and mount if from inside. It's definitely cleaner, but I've also considered just bolting it down from the top like you see it pictured here, and cut a slot right below that row of pads where the wires come up and connect, to route the wiring. Flip a coin I guess. Aesthetics aren't that critical for this thing, since it's a one-off and besides myself and you lot, pretty much nobody else will ever see it.

[mindcrime]

Project Update 06-12-2021

OK, made some progress on mounting that keypad. In the end, yes, I went the lazy way and just mounted it from the top, and dremel'd out a slot underneath for the wires. But c'mon, who are you kidding, we all knew it was going to go that way, now didn't we? 



The keypad bolted securely in place.



Doesn't look too bad - from the side you can't see! 



Not the prettiest job in the world machining that slot in the plastic. But oh well. Visual aesthetics was never a super high priority for this project.



Wires go through here...



This actually wouldn't be too bad, if I had not goofed and machined the bottom edge of the slot down too low, making it visible from the top. Oh well.. dem's da breaks.



A more or less final view of what it'll look like from the top, when finished. There will be some wires coming out the back somewhere, but otherwise most of the parts that involve drilling holes and cutting material are done.

Now the big push will be to finish getting all the electronic bits consolidated onto one (or maybe two) PCB's, and then mount the boards, including the Arduino and the thermocouple amplifier, inside somehow. I'm almost tempted to whack an edge card connector in there, and do the final assembly on a board that fits one of those (ISA style) so I can slide it in and out easily. 

[mindcrime]

Project Update 06-15-2021

I'm starting to get an idea of how this control box is going to come together, I think.



I added female header connectors to the wires coming off the keypad, which will terminate at a row of male header pins that will live on the board that hosts the keypad decoder IC.



The keypad decoder stuff is still on the breadboard for now, but will soon move to a dedicated board of its own. Which will couple with:



This power supply board, which I've decided to leave unmodified (ie, I'm not moving that one lonely transistor to this board after all). Because...



I realized that the board with the one lonely transistor is a perfect spot to cram the arduino and the thermocouple amp.

This gives me 3 boards, which I'll stack vertically using threaded hex standoffs. I'll then mount the board assembly by securing some threaded standoffs to the bottom of the enclosure with JB Weld or resin, or whatever.

I also need to add a way to get the 12VAC feed into the enclosure, and an interface for the signal to the SSR. I'm leaning towards mounting banana plug connectors on the back of the oven and on this enclosure, and making the connection with a set of what would basically be banana plug jumper cables.
 

[mindcrime]

Project Update v2, 06-15-2021

Got started making that board that will hold the keypad decoder stuff. Not a lot of progress, but enough to count for something I guess.



Soldered some headers on the board, and starting to put in a socket for the 74C922 decoder IC.



Keypad wires just plug into the headers. Simple.



Get that socket soldered in place and the battle is half won!



I screwed up on one pin and lifted the little copper pad off the board. No biggie though. When I bring in a wire to solder to that pin, the pin and the wire will be locked together and the wire can bond to the pad around the hole it comes through. And it's not like the socket is going to go anywhere with the rest of the pins soldered in place.



Now to put the socket in place for the 74HC04 inverter. Those two chips and a couple of capacitors are all that go on this board, besides header pins and wire.



Both sockets in place and the IC's (temporarily) seated. Looking snug!

Now to add the headers for output and power connections, add the capacitors, and wire everything up. At that point, this thing will be very close to finished!

[fourfathom]

Way to go!  FYI, I prefer to use double-sided perfboard with plated-through holes for this kind of breadboarding.  It's a bit more difficult to modify (than the single-sided phenolic board) once the components are soldered, but the connections are way more secure and the boards themselves are much stronger.

I can't wait to see how runs when you've got it all put together!

[coppercone2]

I can only stand veroboard and all the other ones are torture to use

just leave it on a breadboard and melt the first pcb with it

[fourfathom]

I can only stand veroboard and all the other ones are torture to use

just leave it on a breadboard and melt the first pcb with it

Veroboard with the copper strips, right?  That's never seemed handy to me.  I always needed so many cuts and jumpers that I would rather just strip and solder wire-wrap wire between isolated pads, and lay down / tack-solder a few bare wires as ground and power busses.

I'm really dating myself here, but I used wire-wrap to build a very early 6800 processor board for an industrial control system.  Later I used that thin wire with the solder-through insulation.  These days I either build simple stuff on a perfboard, or mill a simple circuit board, or for more complicated designs send the gerbers off for fab.  I just had a bunch of simple 1"x1" boards made for SMA attenuators.  Ridiculously cheap at about $0.20 each. and about the same for shipping (qty 50).

[beanflying]

The few boards like Mindcrime used here I had got trashed for assorted Spacers in woodworking jigs and non Electronics use. I got tired of the pads departing from the substrate.  Anything that advertises itself as 'Double Sided Prototype Board' is a much better thing eBay auction: #233880123981 I keep a few sizes and also some alternate pitch versions for odd ball jobs.

Back on topic looking good 

[coppercone2]

if you use the stripping tool and its sharp for veroboard (or a drill if you don't mind it being weaker), it is efficient

if you use an exacto instead of a rotary cutter then thats your problem.

[mindcrime]

if you use the stripping tool and its sharp for veroboard (or a drill if you don't mind it being weaker), it is efficient

if you use an exacto instead of a rotary cutter then thats your problem.

I bought a new drill bit set the other week, just to keep at my bench so I can use one of the bits for cutting Veroboard strips. Haven't even used it yet. I keep Veroboard, single sided protoboard, double sided protoboard and all sorts of miscellaneous stuff here, but those cheap little single sided boards just happened to be close at hand when I started on this. It would probably have been easier to use the Veroboard... oh well. Next time.

The few boards like Mindcrime used here I had got trashed for assorted Spacers in woodworking jigs and non Electronics use.

Heh. I do the same thing, FWIW. These things are so handy for all sorts of miscellaneous uses. Sometimes I grab one and use the bare side as a sacrificial surface to solder on (when joining wire to wire, or wire to connector, etc.) instead of leaving the thing laying directly on the blue ESD matting. They also make handy shims / spacers for all sorts of applications. 

[mindcrime]

Project Update 06-19-2021

In the previous episode we saw the bare outlines of a circuit board for the keypad decoder logic starting to take shape. Today we see how things have progressed from there.





And it's done. Or is it "done"? Hmm.. time will tell. But all the parts are on the board and everything is wired up. Nothing to do now but remove left over flux and test it. *gasp* "test"? That can't be a good thing...



Keypad connected, Arduino connected, and no more breadboard crap in the way. Time to see what this baby can do!





It's this point in the story where our erstwhile hero realizes that critical mistakes have been made...   





Fortunately the error was no more than mounting the display upside down. 



After a bit of fiddling with the correct ordering of the jumpers coming from the keypad to the board, we're back to being able to correctly decode keypresses and respond to them.

Not much left on the hardware side now, aside from mounting these three boards in the box, wiring everything up, and finalizing the arrangements for how the control box is going to connect to the oven. I continue to lean towards the idea of using banana plug jacks on both ends (oven and control box) with the connections made with cables with male banana plug connectors on each end.

After that, I can continue to tune and iterate on the software part, but I think the software already provides something usable.

I also need to integrate the piezo buzzer that is going to signal when a profile run is finished.

Oh, and then there's the whole door opener thing. I'm still punting on that, largely driven by the fact that the linear actuator I bought, while it would work fine, is honestly too big for this application. I am going to evaluate buying one that's better suited,or perhaps even consider switching to using a servo instead. No hurry on that bit though. I can open the door by hand for now.

My SOIC-14 stencil and some more NE555 IC's in SOIC-14 just came in, so soon I'll resume doing some test solder jobs and see how much nicer things turn out when the solder is properly applied. 

[mindcrime]

It's always the dumbest things that trip you up. So I'm sitting here working on assembling / packaging all of this stuff, and I get the thermocouple amplifier board bolted to the piece of perfboard that is going to hold it. Then I start to bolt the Arduino Nano 33 IoT down and ... promptly come-a-gutsa. The stupid mounting holes on the Nano 33 board are like 0.07" in diameter... too small for the smallest machine screws I have here (#2). And there's really no room to drill the holes out any larger, without risk of damaging something.

Sssssooooooo... off to McMaster Carr to order a bag of #1 machine screws and matching nuts. Those supposedly work with 0.073" holes, which should be close enough. Worst case I take a tapered file and ream the hole out by 3 thousandths of an inch. Maybe I should have bought some #0 screws as well, just to be on the safe side...

*sigh*
 
Maybe I should just hot-melt glue the bloody thing into place.

[fourfathom]

Could those be "M2" screws (2 mm dia, slightly smaller than "#2")?  These days a lot of small boards use the metric M2 hardware.  Me, I grew up using #6 and #4 screws for this stuff, but recently I was assimilated and bought some M2 assortments: various screw, nut, washer, standoff, etc kits in stainless, brass, and plastic.  Cheap, from China, via Amazon.

[mindcrime]

Could those be "M2" screws (2 mm dia, slightly smaller than "#2")?  These days a lot of small boards use the metric M2 hardware.  Me, I grew up using #6 and #4 screws for this stuff, but recently I was assimilated and bought some M2 assortments: various screw, nut, washer, standoff, etc kits in stainless, brass, and plastic.  Cheap, from China, via Amazon.

Probably. And yeah, I've thought about ordering an assortment of the metric ones. I'm not, even as a red-blooded 'Murican, opposed to metric stuff at all. I keep using SAE / Imperial stuff out of habit more than anything. I guess it's time to catch up with the modern world and switch over wholesale.

[beanflying]

Arduino sizes and screw placements generally SUCK. I keep some 2 and 2.5mm plastic hardware principally for them. In the case of the UNO you risk shorting bits out with metal fastners and in particular if you enlarge the holes.

As an R/C flier and being of a certain Age and an Aussie I still talk 2-56 and 4-40 and have even been known to have conversations with farmers in Rods and Chains 

[mindcrime]

Arduino sizes and screw placements generally SUCK. I keep some 2 and 2.5mm plastic hardware principally for them. In the case of the UNO you risk shorting bits out with metal fastners and in particular if you enlarge the holes.

Good point. Maybe I should order up some nylon screws just to be on the safe side.

As an R/C flier and being of a certain Age and an Aussie I still talk 2-56 and 4-40 and have even been known to have conversations with farmers in Rods and Chains 

Do you measure weights in "Stone" as well? 

[mindcrime]

More baby steps towards making this a finished project.




Instead of just having wires flapping around in the breeze, I added header pins to connect the output from this board. One set for ground, one set for 5V and one set for 12V.  No, the placement isn't optimal, but honestly, these were an afterthought. Not to suggest that much "thought" went into the layout of the board in the first place. 







A handy little adapter to power the Arduino from the header pins on the power supply board.



A pair of banana plug connectors for the SSR control.



And a pair to receive the 12VAC feed from the transformer mounted in the oven case.



Now, I just need all of this crap, er stuff, erm, I mean,  "electronics" securely and neatly mounted in this box somehow, and all the wiring connected. 

Idea #1 - wire everything up, cram the boards in there more or less as  you see, and then fill the whole dang thing with resin! 

Idea #2 - run back and forth to McMaster Carr, the local Ace hardware, my parts bin, etc., frantically scrambling to cobble together the right combination of standoffs, washers, machine screws, nuts, epoxy, etc. necessary to allpw me to spend hours painstakingly drilling holes, bolting things together, and tediously assembling this into something that I could be proud of (if I were on a really bad acid trip, and had no standards, and knew no one else would ever see it).

*sigh* as much as I hate both ideas, I suppose #2 will carry the day. Maybe I should make a version doing the resin thing though, and see if I can get it displayed at the Museum of Modern Art or something. 

[mindcrime]

OK, it's not quite Idea #2, but it's not quite as bad as "pot the entire assembly in resin" either. In the end, I went with the one mounting technique I most specifically did not want to use. And that's "drill holes all the way through the sides of the box and use machine screws and nuts to bolt the boards to the sidewalls".











And yet, that's exactly what I did in the end.

"So why", you may be asking, "did you do it the one way you didn't want to do it? And why were you so opposed to doing it that way in the first place?"

Glad you asked. To answer those questions in reverse order:

1. I didn't want to do that because it's ugly. And while visual aesthetics aren't goal #1 of this project, I also wasn't exactly looking for the "Mad Max aesthetic" look and feel. Or would this be the "Dr. Frankenstein's Lab aesthetic" look and feel?

2. I did it because it was the one technique that let me make progress with the hardware I had handy, without waiting for a bunch of bolts and standoffs and other hardware to be delivered. Also, my original plan was to stack the boards vertically with standoffs separating the boards, but the more I look at it the more I think that would make it really hard to deal with all those jumper wires. And for now, I really don't feel like getting rid of those. Having the boards mounted vertically on the sidewalls leaves all that room in the middle for wires to bend and flow and makes repair access for the future relatively easy.

Also, and maybe the biggest deciding factor, was an epiphany of sorts that I had. I think there will be a clean way to come back and get rid of the gnarly looking bolts and nuts on the sides. Since I already drilled holes all the way through, I'm thinking I can come back later and add those heat-press-fit threaded inserts where the holes are now, and press them to where they're flush with the edge of the case (or even slightly countersunk). Then I can just paint over the outside and/or putty over the blemishes with a little JB Weld or something. Then the mounting from the inside will be exactly the same, there just won't be a nut on the other side of the wall. And if that doesn't work, well, I can always keep the Dr. Frankenstein's Lab look, or buy a new box and do something different altogether.

Also, yes, I know that one board is bowed pretty badly. I need to dig my bag of nylon spacers out of the big-heap-o-parts-boxes later. I'll find some and redo all of those with spacers to keep the boards from bowing like that.

[mindcrime]

Project Update 06-29-2021

So, in the end, I did have to order more hardware and tools and wait for that stuff to be delivered. The existing mounting holes on the Arduino Nano board turned out to be sized for a metric M1.6 screw, and I had no M1.6 screws, nuts, etc. nor a 3.5mm nut-driver, here. But, I got that stuff ordered, after some fits and starts, and now all the board mounting is worked out. I just need to un-mount all of these, add spacers as appropriate to keep from flexing the boards, and then re-assemble it, and the physical fabrication on this box is down to about the next to last punch-list item (cutting a slot in the top for the wires that go to the LCD display to pass through).






I did goof on one aspect of this though. That board that carries the Arduino Nano got mounted too high up and didn't leave enough room for the (previously made) straight USB cable power adapter. Luckily I keep a bunch of the right-angle USB cables around here as well, so I cut one of those up and am re-making the power adapter with that.

[mindcrime]

Project Update 06-29-2021 episode II

Managed to make some more progress this evening after work. And I think finally, mercifully, I can now say I'm done with everything that involves opening up the actual oven. Even better, there are now no more unsightly (and unsafe) wires snaking through razor-edged ventilation slots.



Banana plugs. Ugly, yes. But effective.



It is physically impossible for me to drill holes for mounting banana plugs and get them to line up properly. Of course, if I would measure and mark this stuff instead of trying to "eyeball" it all the time....



Looks even worse from the inside. But nobody will ever know but us, right?






Connectors affixed, and now I can close this baby up!



These all run to the matching connectors on the control box.



Green is my 12VAC output which provides power to the control box. Why green? I dunno. It was handy. And I tend to associate the color green with AC wiring for some weird reason.



AC output still works. Yay!



The other end of the connection. You can start to kinda see how it all comes together...







Lid re-installed, and the control box attached to the oven. This is very close to finished now. Just a few more tweaks on the control unit and we're ready to solder.

[beanflying]

Strange but some of your images are blocked for me 



And some of them really are too. Whoever or wherever you are hosting your pictures seems to be bandwidth limiting 

[mindcrime]

Strange but some of your images are blocked for me 



And some of them really are too. Whoever or wherever you are hosting your pictures seems to be bandwidth limiting 

Aarggh... Google Photos is stupid. I need to switch to a different image hosting setup, but it's just so convenient to rely on GPhotos since my Android phone automatically uploads pictures for me, etc. **sigh**

Aaah well. Not sure what to say. I did try loading this thread from an incognito window in a different browser that had not visited this thread before, to eliminate both login cookies and cached images, and yet all the recent pictures showed up OK for me. Maybe it's just some transient network error or something? Who knows...

[fourfathom]

I can't see the images in this post: https://www.eevblog.com/forum/projects/finally-starting-on-this-convection-oven-gt-reflow-oven-conversion-project/msg3592043/#msg3592043
All the others, including your latest, look fine.

And congrats on your good progress.  A couple of days ago I used my oven to reflow a batch of RF attenuators.  I needed a better assortment of SMA attenuators and didn't feel like buying them.  So I did the complicated and time-consuming thing of laying out a small PCB, using custom footprints for the resistors that would accept anything from 0402 to 1206 surface-mount sizes.  It's just a simple Pi network, with parallel resistor locations that let me use my assortment of 1% resistors (I stock the 5% series) to get the desired resistance.  So far I've made 10dB and 20dB pads, and they are flat within 1/10 dB from DC to 1 GHz, and within 1/2 dB to 2 GHz -- way better than I had anticipated.  The return loss is decent for my needs, better than -30dB to 1 GHz.  I have through-holes around the board perimeter to let me add a shield cover if I want to try that. I used JLCPCB, 50 boards for 20 cents each, plus $13 for shipping.  Crazy!

I finally got a small-diameter syringe tip  for the solder paste, and while it takes a whole lot of force to work the syringe I can put small dots of paste on the pads.  I hand-soldered the SMA connectors, but I'm going to try a few in the oven to see how they hold up.

[mindcrime]

I can't see the images in this post: https://www.eevblog.com/forum/projects/finally-starting-on-this-convection-oven-gt-reflow-oven-conversion-project/msg3592043/#msg3592043
All the others, including your latest, look fine.

Weird. I don't always understand how GPhotos decides what to allow and not allow. Once I added the Chrome "get GPhotos link" extension to my browser and started using those links, it seems to mostly work, but even then I guess it's hit or miss. **sigh**

I finally got a small-diameter syringe tip  for the solder paste, and while it takes a whole lot of force to work the syringe I can put small dots of paste on the pads.  I hand-soldered the SMA connectors, but I'm going to try a few in the oven to see how they hold up.

Nice. What size tip did you wind up using? I might look into getting some of those and see how it works.

I did get a bunch of additional "stock" stencils from ChipQuik the other day. Now I have stencils for single chips in most of the common SOIC layouts and a couple of other common ones.

[fourfathom]

I used this syringe kit from Amazon: https://www.amazon.com/gp/product/B08G8XNFKK
The short #18 needle gave me a reasonable solder dot for my resistor pads, but it would have been much too big for my 0.5mm-pitch IC pads.  I suspect that if I had used a smaller needle I would have cracked the plastic syringe from the necessary pressure.  It took some practice to get the solder to stick to the pads rather than stay adhered to the tip, and I sometimes used a small wire to push the solder around (and then the solder would want to stick to the wire).  But by the third board I was getting the hang of it.  The solder was at around 70 deg F).  This needle was 1" long, probably a shorter needle would require less pressure to get the paste to flow.  It's a work in progress and stencils are cheap, so "good enough" is OK with me.

I had originally got the syringe needles to use with a vacuum-pickup for grabbing and placing components, but so far I'm still using tweezers.

[coppercone2]

You have a scrap of metal in one of your banana plug holes that can potentially come lose and make a short circuit, get that fixed ASAP. Typical drilling near metal stampings problem, take a close look


If you want 'cleaner' holes in shitty metal, you can think about this tool:
https://www.amazon.com/Astro-Pneumatic-Tool-1442-Setter/dp/B003TODXQW/ref=asc_df_B003TODXQW/?tag=hyprod-20&linkCode=df0&hvadid=312174136943&hvpos=&hvnetw=g&hvrand=13597386352196417469&hvpone=&hvptwo=&hvqmt=&hvdev=c&hvdvcmdl=&hvlocint=&hvlocphy=9004235&hvtargid=pla-338189070626&psc=1&tag=&ref=&adgrpid=63790029762&hvpone=&hvptwo=&hvadid=312174136943&hvpos=&hvnetw=g&hvrand=13597386352196417469&hvqmt=&hvdev=c&hvdvcmdl=&hvlocint=&hvlocphy=9004235&hvtargid=pla-338189070626

you can put nuts into the chassis, drill out the thread, and seat the banana plug in it, if you want it in a neat grommet


you might want to look at getting cable harnesses or at least looking at pin and socket for those wires so you can unhook the boards without a soldering iron, its starting to look hairy. You don't need the cable housing, you can put aviation pins on the PCB and crimp or solder sockets on the wires. not sure whats going on in there, maybe you soldered them to headers

[mindcrime]

You have a scrap of metal in one of your banana plug holes that can potentially come lose and make a short circuit, get that fixed ASAP. Typical drilling near metal stampings problem, take a close look

Thanks, I was able to grab it with a pair of needle-nose pliers and yank it out.

If you want 'cleaner' holes in shitty metal, you can think about this tool:
https://www.amazon.com/Astro-Pneumatic-Tool-1442-Setter/dp/B003TODXQW/ref=asc_df_B003TODXQW/?tag=hyprod-20&linkCode=df0&hvadid=312174136943&hvpos=&hvnetw=g&hvrand=13597386352196417469&hvpone=&hvptwo=&hvqmt=&hvdev=c&hvdvcmdl=&hvlocint=&hvlocphy=9004235&hvtargid=pla-338189070626&psc=1&tag=&ref=&adgrpid=63790029762&hvpone=&hvptwo=&hvadid=312174136943&hvpos=&hvnetw=g&hvrand=13597386352196417469&hvqmt=&hvdev=c&hvdvcmdl=&hvlocint=&hvlocphy=9004235&hvtargid=pla-338189070626

you can put nuts into the chassis, drill out the thread, and seat the banana plug in it, if you want it in a neat grommet

Huh, interesting. I'll definitely look into that for future use. So far the best way I've found to drill decent holes in think/weak metal is to sandwich the metal between a couple of sacrificial pieces of wood, clamp the wood down tight, and drill through the whole mess. I didn't have enough room to do that that here though. 

you might want to look at getting cable harnesses or at least looking at pin and socket for those wires so you can unhook the boards without a soldering iron, its starting to look hairy. You don't need the cable housing, you can put aviation pins on the PCB and crimp or solder sockets on the wires. not sure whats going on in there, maybe you soldered them to headers

Sorry, I'm not following you. You can unhook everything now with no soldering. 95% of the board to <anything else> interconnections are done with dupont header pins and corresponding connectors. The couple of exceptions are the USB connection to the Nano, and the input to the power supply board, which (when I finish that bit) will terminate at the banana plug end with some ring connectors that can be connected/disconnected from the banana plug.

Heck, even the couple of IC's I added are socketed. I am very big on making things that are easy to disassemble / modify / repair.

One problem I have, although not one I care enough about to "solve" is that I'm using pre-made / store-bought jumpers to connect things, and in many places they are much longer than they need to be, so I wind up with a rat's nest of wire coiled around in there. At this point my innate laziness / apathy kicks in, and I doubt I'll ever bother addressing that. If I were making a product to sell, I would absolutely worry about that. For a one-off tool built for my own use? Nah. Not gonna sweat it.

[coppercone2]

then its fine, too many pictures failed to load and I thought it was soldered together. if the wiring in mine was all soldered together I would possibly throw it out if it breaks because its just too much

the wood trick works but sometimes if you are drilling a stamping its very hard not to tear it and the only way to get a 'good' hole is to put some kind of grommet in it like a shower curtain

I built 'cool' projects before that I thought could work like paint can mini variac and there is a perpetual problem with getting banana plugs into the metal to sit nicely, the only way is some kind of reinforcement, and you get this problem a little with certain tins (like foodstuff for cookies or soup cans or whatever).

I made a somewhat nice paint can variac and the banana plugs and stuff kept getting loose every few months, so as a rare use item every time I went to use it it needed some kind of maintenance

If I had the tool I linked you when I made it, I could put thick stable deformed metal nuts into the thin crappy metal to have a really good place to put the connectors on stable surfaces. I would just need to drill the nuts out a little bit. 

[mindcrime]

then its fine, too many pictures failed to load and I thought it was soldered together. if the wiring in mine was all soldered together I would possibly throw it out if it breaks because its just too much

Yeah, same here. That's a bit of a "thing" with me. I hate items that can't be taken apart without (desoldering|cutting wires|any other unnecessary effort). So it would be very hypocritical of me to build something like that myself!

If I had the tool I linked you when I made it, I could put thick stable deformed metal nuts into the thin crappy metal to have a really good place to put the connectors on stable surfaces. I would just need to drill the nuts out a little bit.

Yeah, I am definitely wanting one of those now. I had not seen those before, so thanks for pointing that out.

[coppercone2]

just check the dimensions to make sure its compatible with a banana plug, it was just a thought

Also, I am not sure how well it grounds for grounded BNC if you want to use it in other projects.

I just have had very bad experiences with reusing thin metal enclosures to the point where I will buy a box for small stuff. For large stuff like that tool is intended for, I prefer to braze on nuts with a torch, but it has its purpose if you don't want to disturb a paint job or are working on weird objects. for chassis work that tool is a game changer for certain things. and possibly a massive cost and weight reducer since it lets you use thinner metal that is normally avoided because its hard to fasten nicely (obviously it might have EMI issues but for standard lab equipment and tools its great)

I kind of wish I had it for my project because then I could put fastener holes inside of the toaster oven to bolt my box onto, I did something very difficult with nuts, pliers and crazy tight wiring that required a mirror and mini right angle tools (it will still disassemble but you might want to throw something)

However I did do a good job and the PID I have goes into a big socket so if it breaks I can theoretically replace it just undoing 2 screws

[beanflying]

Nutsert tools are great for panel work. The angled guns rather than the longer ones are more useful to get into small spaces. Add a set of step drills to your collection too if you don't already have them. Both used here for a run of M6 Stainless Nutserts to retain some acrylic screens on some food benches.

[mindcrime]

OK, putting the finishing touches on this. With one minor exception, all of the electrical/electronic work AND physical fabrication work is DONE for what I'm calling "Phase 1". There will be as subsequent "Phase 1.1" or something like that, and perhaps a "Phase 2", but this phase yields a usable tool, which was the goal.

The one remaining work item, besides tuning the software, is to add a heat-sink on my LM7805 voltage regulator. It's running a little bit warmer than I'd prefer. I thought I could get away with it as is, but between the Arduino and the LCD, it pushes it just hard enough to where it gets a bit warm.

Anyway, some pics of the progress to date.





Finally cleaning up the mounting of the boards, adding spacers to keep the boards from flexing, etc.



I built a couple of long banana-to-banana jumper cables out of unused extension cords. This way the controller can sit on the bench while I tinker with it, but actually run the oven "live" for testing.



And wired up those banana plug connectors on the inside.



And that's pretty much it. The whole thing, all packaged up and ready to use (modulo some software tweaks).





Powered up and displaying the default greeting on the LCD.



The view from behind.

Anyway, that's basically it. I'll add that heatsink, finish merging the bits of software that I had originally developed in different projects, reflash the Arduino, and I'll have a usable reflow oven.

Things for "Phase 1.1" - adding the piezo buzzer that will buzz when the profile run is finished. I'm just not motivated to work on that right now. I need a break from this for a little while.

Things for "Phase 2" - finally implement the automatic door opener, and maybe design a real PCB for the electronics, mill it out, and solder it **in this very oven** and then rebuild everything in what will hopefully be a much cleaner / more elegant fashion. The circuit board layout / design here was really ad-hoc and kinda "making it up as I go" and could be way improved. It works, but some of the choices I made wound up making things difficult in the final assembly phase, and don't lend themselves to making this easy to maintain / repair, etc.

"Phase 2" might also include heat-press-fitting threaded inserts where the board mounting screws go, and not have that stuff sticking through with those nuts on the outside. If I do, then I could turn around and use a little dab of epoxy / bondo / J.B. Weld / etc. to cover over the holes so everything looks nice and smooth from the outside.

Edit: also if anyone is wondering, no, I don't intend to leave the control box sitting on top of the oven when it's in use.  That's the whole reason for the long jumpers connecting the box to the oven, so I can set it off to the side while the oven is actually running. The one thing I should probably also consider, is using a longer thermocouple wire. I think the kit I ordered included two, the one seen here, and one much longer one. That is, if memory serves correctly. If so, I should probably swap it out, as right now that thermocouple is the limiting factor in how close the control box has to be to the actual oven.

[mindcrime]

Code for this project is up on Github.com now. See: https://github.com/mindcrime/ReflowOven

I kinda stalled out on this right after posting the last message above, and didn't get back to working on those last few software tweaks until last weekend. But now that I'm back on it, the software part should all be finished up in another day or two. All of the pieces are there, they just need to be integrated into a comprehensive unit and flashed to the Arduino.