Author Topic: Soldering station controller for Hakko Irons!  (Read 2266 times)

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Online cowana

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Soldering station controller for Hakko Irons!
« on: January 09, 2013, 09:44:26 AM »
For soldering at home, I use a Hakko hot air rework station.  This has a hot air gun, and a standard Hakko soldering pencil (24v, 50W).

My current soldering station is bulky, not portable, and has very poor temperature control (bang-bang rather than PID).  I would like to design and build a new controller to be used with Hakko soldering irons. This should provide much better control to the iron, allow more features and customization, and be much more portable.

The current specifications:
  • 240v AC mains input (rear IEC socket)
  • Internal 60W, 24v toroidal transformer
  • Support for virtually all 24v soldering irons
  • Able to read the temperature of K-type thermocouple and PTC thermistor irons (selectable via an internal jumper)
  • Full PID control of temperature
  • Auto standby mode if left in the stand for a certain time (able to tell that from monitoring tip temperature/power requirement)
  • 'Turbo mode' activated by a button (increase temperature by 50 degrees for 30 seconds)
  • Variable temperature
  • Multiple preset temperatures
  • All in a neat, compact, aluminium case

Most of those are pretty standard features for a soldering iron driver - including both thermistor and thermocouple sensing sections on the PCB mean I'll be able to carry on using this driver whatever soldering iron I want to use (in other words, when I can afford something nicer than Hakko pencils!).

I'm doing this project as building things is my hobby and it'll be a fun process, rather than a real need for a better iron.  I'm hoping to come up with a controller that looks great and controls temperature better than my current station's bang-bang control.


So - the really important bit - the front panel! This is the bit the user (me) will really see, so I want something that looks nice and cool.

I'm currently planning to manufacture the entire front panel of the box out of dark tinted plastic, with the display behind it.  In the centre of the front will be three 7 segment displays, showing the set temperature.  In a circle around this there will be a circle of 40 red/green bicolour LEDs, which will act as a circular LED bargaph. The set temperature will be shown in red, and as the iron heats up, the LEDs will fill the bar up with green. Sorry if that's a poor description, it looks good in my head!

Presets/turbo would be selected with illuminated tactile buttons - or standard tactile buttons surrounded by LEDs if low profile SMD illuminated switches are too hard to find. Possibly (blue sky thinking here!), use non-contact capacitive sensing for all front panel functions?

I'm having mixed thoughts on what the temperature input should be:
Potentiometer
  • + Very fine control
  • + Very fast control
  • + Easy to read in software
  • - Will be changed/knocked if station is transported elsewhere
  • - Harder to adjust presets etc

Rotary encoder
  • + Easy to make adjustments to presets
  • + Very versatile (can change software)
  • - Most of the time you want big steps, other times small changes
  • - Requires interrupts in software
  • - Very few soldering stations use them - probably a reason for that

Up/Down buttons
  • + Easy to make adjustments to presets
  • + Looks neatest on front panel
  • + Can implement fast changing if held down
  • + Most digital irons have buttons!
  • - Requires interrupts in software
  • - Could be a fiddly interface if done poorly

My current view is up/down buttons are the best solution - they're least obtrusive, don't stick out at all, and probably work best with adjusting presets.  Capacitive buttons could work really nicely here! A rotary encoder seems unsuited for this - most of the time you want to be able to change temperatures without having to turn a knob multiple times.

Any thoughts or comments would be very welcome. Got any feelings about what the ultimate soldering iron controller should have? Can the front panel be made any cooler than having a circular red/green bargraph around the LED readout?

Looking forward to hearing your views!

Andy

Offline FenderBender

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Re: Soldering station controller for Hakko Irons!
« Reply #1 on: January 09, 2013, 10:46:31 AM »
I think knobs are more intuitive. I hate buttons on a soldering iron. That's my opinion. And rarely do you need like say 280 degrees on the nose. Like 270 or 290 would do the trick also.

Just my opinion.

Offline SLJ

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Re: Soldering station controller for Hakko Irons!
« Reply #2 on: January 09, 2013, 11:56:41 AM »
+1 on Knobs better than buttons. 
My Weller digital station has a knob.  :-+   My rework station has buttons.  :-- PIA
My old old Weller soldering station has nothing except a 700 degree F tip.  It gets the most use and will still outlast anything out there today. 30+ years and going strong.

Offline Nirios

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Re: Soldering station controller for Hakko Irons!
« Reply #3 on: January 09, 2013, 02:06:25 PM »
Thought you might want to check out: http://dangerousprototypes.com/docs/Soldering_Iron_Driver
The board design is listed as public domain.

I like your idea of the circular LED display.  You could also try a small two color OLED display but that may drive the price up too much.  Also +1 for the rotary encoder vs buttons.

Online cowana

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Re: Soldering station controller for Hakko Irons!
« Reply #4 on: January 09, 2013, 07:42:23 PM »
It sounds like a rotary encoder is the method to use - I'll go with a high number of detents per revolution (probably 36), with each detent probably representing 5 degrees.  That should be pretty quick to use - a full turn would change the temperature by 180 degrees.

Another big advantage of a rotary encoder, is using one with a push switch means I can get rid of all the other buttons! By holding it down, it can enter a menu for selecting presets 1,3, turbo mode etc. A front panel with no buttons always looks neat.

Niros - the DP project is one of the factors that inspired me to do this project.  However, my version will have a few changes:
  • I'm not a fan of 16x2 LCDs where you only want to show a few characters (temperature).  The text is too small compared to 7 seg displays.
  • I plan to rectify the AC and switch it to the iron with a FET.  This means I don't need to bother with any zero crossing detection/switching.
  • They use one opamp for both the thermocouple (big gain), and the thermistor (big gain followed by big attenuation). I plan to use an opamp for the thermistor, then a proper thermocouple reader (maxim) to read that accuratly.
  • It seems now I'll be using a rotary encoder and menu interface!

I'm imagining I'll make something quite similar to http://eosystems.ro/index.php/projects/esol, although with a much nicer front panel and more LEDs.

Keep any ideas/thoughts coming :)

Andy
« Last Edit: January 09, 2013, 09:11:33 PM by cowana »

Offline nukie

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Re: Soldering station controller for Hakko Irons!
« Reply #5 on: January 09, 2013, 08:24:29 PM »
I prefer knob, I am so used to my station I can dial up and down without looking at the panel.


Offline flolic

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Re: Soldering station controller for Hakko Irons!
« Reply #6 on: January 09, 2013, 09:09:22 PM »
Knob is always my first choice because it's so simple, fast and intuitive. And by knob I mean potentiometer with scale.
Rotary encoder can work too, but it's annoying to turn it while watching display, when you can set potentiometer in a blink of a eye  ;)
Push buttons are big no, except if you have two or three buttons with presets.
All my life I have been using analog stations with potentiometer, but recently I bought digital station (Atten 315D) with push buttons. It is awkward to push button and wait for desired temperature, but station has three presets that I set to 315, 350 and 400 Celsius and that is more than I actually need. Also, it reaches desired temperature in a second or two, so it's real joy to use.
In the end I prefer two options, pure "analog" style potentiometer, or as simple as possible "digital" buttons with presets.

Offline amyk

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Re: Soldering station controller for Hakko Irons!
« Reply #7 on: January 09, 2013, 09:45:27 PM »
How about a knob + analogue meter for indicating the current temperature? That's something I've not seen in a soldering station before.

Online cowana

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Re: Soldering station controller for Hakko Irons!
« Reply #8 on: January 12, 2013, 05:08:01 AM »
Using an OLED instead of the seven segment displays is a very neat idea and could look very nice.

Any thoughts/experience on where to get a nice graphic oLED (probably monocolour)?  Probably one compatible with one of the common graphics libraries such as http://code.google.com/p/u8glib/ :).

Thanks,
Andy

Offline jeroen74

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Re: Soldering station controller for Hakko Irons!
« Reply #9 on: January 12, 2013, 08:00:26 PM »
Try eBay. There a few ready to use boards available so you don't have to deal with the awkward finepitch foil type soldertabs to solder all these OLED display have.

Online cowana

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Re: Soldering station controller for Hakko Irons!
« Reply #10 on: January 28, 2013, 11:54:52 PM »
I've done a bit more work on the project, made the decision to stick with 7 segment LEDs for the temperature, with a circular bargraph round them (made up of 24 bicolour LEDs). All LEDs are driven through shift registers, meaning the micro doesn't have to bother with multiplexing and can concentrate on PID control.

Most soldering stations use triacs to switch AC to the soldering iron - however I'm going to use a FET, meaning I can just send it PWM.  As 24v rectified and smoothed gives ~34v, I'm planning to feed the soldering iron with plain rectified AC, rather than adding a capacitor to increase the voltage, meaning 100% PWM is not going to damage the heater.

Most soldering irons have K type thermocouples or thermistors, so I'm including both a potential divider and Maxim thermocouple reading chip (SPI).

Any comment or thoughts on the attached schematic are most welcome!

Andy

EDIT: Attachment updated to version with all GND connections shown
« Last Edit: January 29, 2013, 02:29:40 AM by cowana »

Offline jeroen74

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Re: Soldering station controller for Hakko Irons!
« Reply #11 on: January 29, 2013, 12:15:06 AM »
The MCU does not mind doing the multiplexing, it only takes a couple % of the MCU bandwidth. I would have used an USB-equipped AVR model, like the 32U4. Anyway, a couple of points:

* You should add a pull-up resistor, a protection diode and small cap on the reset line.
* OSC1, is that a resonator or a crystal? If the latter, you should add load capacitors.
* The common cathodes of the LED displays are not connected to ground. Both the 7 segment and the bi-colour ones.
* I would add series resistors for the encoder contacts. Basically the encoder contacts now short-circuit the capacitor.

Online cowana

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Re: Soldering station controller for Hakko Irons!
« Reply #12 on: January 29, 2013, 12:45:23 AM »
* You should add a pull-up resistor, a protection diode and small cap on the reset line.
The AVR does have a high value internal pullup, but I'll stick an external one on too to make sure.

* OSC1, is that a resonator or a crystal? If the latter, you should add load capacitors.
It's a resonator, so it'll be fine without.

* The common cathodes of the LED displays are not connected to ground. Both the 7 segment and the bi-colour ones.
I made the connection by linking the nets - so it is connected, just not shown clearly in the schematic. (That's why the cathodes connections are coloured blue)

* I would add series resistors for the encoder contacts. Basically the encoder contacts now short-circuit the capacitor.
Would that still be required with low value (say 100nF) capacitors? I guess the easiest way to do it would be add a low value resistor to the common line...

Thanks for the thoughts.

Andy

Offline jeroen74

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Re: Soldering station controller for Hakko Irons!
« Reply #13 on: January 29, 2013, 01:47:42 AM »
Quote
The AVR does have a high value internal pullup, but I'll stick an external one on too to make sure.


Don't forget the diode, the RST pin does not have an internal diode to VCC to protect it, like all others. It's recommended practice in AVR040.

Quote
I made the connection by linking the nets - so it is connected, just not shown clearly in the schematic. (That's why the cathodes connections are coloured blue)


I hate these Schematic 2.0 style schematics... net names are meant for busses.


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