How to detect when soldering iron removed from holder

[cverburgh]

Hi Everybody,

I'm working on a fume extractor setup and would like to have the fans turned on when the soldering iron is removed from the holder. I have a Weller WESD51 soldering station. I have a pair of 12V fans hooked up to a $10 adjustable desk lamp from Ikea but still need to get some ducting installed. I plan on having it hooked up to my central vac line.

I'm looking for some ideas on how to detect when the iron is removed. This would turn on the 12v fans as well as the central vac system. When the soldering iron is returned, the fans and vacuum will turn off. I can handle all the logic of that, I'm just struggling with the actual iron removal sensor.

I thought of a physical switch, but crossed that off the list because of the heat and how bulky it would be. I thought about some sort of proximity sensor, like what's on a typical 3D printer, but am also worried about the heat.

What would you guys suggest to use for this?

[cowana]

How about an IR beam across the inside of the holder, broken by the iron tip?

[CJay]

I know you'd ruled out mechanical switch but it's a springy soldering iron stand, so rig a microswitch with metal lever*, if you choose correctly it'll have enough current capbility to switch the fans directly.

* something like this one:

http://uk.rs-online.com/web/p/products/8421770/?grossPrice=Y&cm_mmc=UK-PLA-_-google-_-PLA_UK_EN_Switches-_-Microswitches_And_Accessories&mkwid=sJail49Mj_dc|pcrid|88057077723|pkw||pmt||prd|8421770&gclid=CjwKEAiA3NTFBRDKheuO6IG43VQSJAA74F77w1jaocbQI_XYiEw1vGg1YF15SlZ664KOhmqwW46-PxoC7_Xw_wcB

[bji900]

How about a couple of wires connected to the power switch of the iron? Every time you turn the iron on the system comes on. If you want to leave it on for a period of time that would be problematic. How about a small magnet in the iron handle and a simple hall sensor? The metcal's have this feature for heating and sleeping when you put your iron on the nest.

[tpowell1830]

Oh wow, possibilities  for the DIYer. How about creating an LVDT so that when the metal tip is inserted in the coil field, the offset voltage will trigger a mosfet to fire a relay? What a fun circuit to build.   
Make a video of it working and post!

[SeanB]

Reed switch with a tiny ( or 3 arranged inside the handle) neodynium magnet, so that placing the iron in the holder closes the relay, or even one of the more sensitive hall sensors to detect the magnets, or even to detect the iron of the unit using a bias magnet and a linear sensor.

If the holder has a closed entry then wind a coil around it ( make sure the spring does not make a shorted turn) and use a simple metal detector or inductive loop sensor to detect the metal part being in there.

[KL27x]

How about an IR beam across the inside of the holder, broken by the iron tip?

+1. Foolproof and simple. Waste not time in trying to find the exact right part with the correct specs, sensitivity, the exact right placement where it is reliable, the time for debugging and tuning, etc.

[nali]

A thermister glued to the metal holder? Would give you a bit of an off-delay as a bonus 

[eugenenine]

The Hakko I just bought has the iron holder mounted to a panel that can pivot.  Then a spring holds it up but the spring is weak enough that the weight of the iron pushes the panel downward and and presses a switch.   Super simple mechanical setup.

[cverburgh]

Thanks for the quick replies!

I like the idea of the IR beam. I have some receiver/transmitter diodes already but never used them, so it would be fun to try them out.

I also have a little micro switch with a lever on it. I was going to use that to turn on a light in my truck bed when I open the bed cover but never got around to it. I'll see how shaky the stand is to see if that would work.

The reed switch idea is interesting, but I'm not excited about sticking magnets on my iron.

I often sit at my desk for a long time with the iron turned on, using it now and then, so wiring it up to the power switch for that isn't feasible as I don't want the loud fans running all the time.

I had never heard of LVDT, but scanned through the link provided. It sounds pretty cool, but I think it's way over-kill for this project!

I'm not sure the thermister would work. Wouldn't there be a delay after I pull the iron out before the fans come on, waiting for the holder/area to cool? I don't wan the complexity of a micro-controller, so there would probably be a fair amount of components, no? Although I guess I would need a few for the IR beam as well.

The fans are just on a switch now, plugged into a 4S Li-Po battery pack. A 3S pack would be ideal, but I don't have any. So far the fans have been ok running around 15V. I'm working on converting an old server PSU to use for this.

I have a 3d printer so making a mount for the additional hardware should be pretty easy.

I'll post a picture of my current setup later tonight.

[tpowell1830]

Okay, so on a tangent, how long do you solder at one given time? A simple foot switch would work if it is not an hour or more it wouldn't be too tedious and you could press with your foot at will.

[PCChazter]

How hot does it get right at the opening of the stand, closest to the handle? You could mount a button there that has a spring loaded piece of tin bent to release the switch when the handle of the iron rests in the holder.

Sent from my XT1563 using Tapatalk

[technix]

You can put a pair of metal contacts on the holder. When the iron is in place it makes contact and an AC detect current passes (AC so it can penetrate oxides) and your circuit can take some measure against it.

[TiN]

ERSA using accelerometer in handpiece for that in ICON series

[mikerj]

Mount the base on top of a strain gauge so you can detect the loss of weight when the iron is removed.  You could use the guts of a cheap set of kitchen scales.

[bji900]

Vision System connected to a PLC to start and stop the system. Should not be too hard...

[nanofrog]

The Hakko I just bought has the iron holder mounted to a panel that can pivot.  Then a spring holds it up but the spring is weak enough that the weight of the iron pushes the panel downward and and presses a switch.   Super simple mechanical setup.

My Weller WD setup does it this way as well. 

Some of the newer series' of tools however, utilize an accelerometer.

[Alex Eisenhut]

idle speculation: find out the idle heat cycling. When the iron is in use, I suppose it will be heating more often/longer than when sitting in the holder.

[eugenenine]

The Hakko I just bought has the iron holder mounted to a panel that can pivot.  Then a spring holds it up but the spring is weak enough that the weight of the iron pushes the panel downward and and presses a switch.   Super simple mechanical setup.

My Weller WD setup does it this way as well. 

Some of the newer series' of tools however, utilize an accelerometer.

Why just use a simple switch when you can over engineer it right

Maybe newer irons can pair with your phone and tell you if your holding it wrong

[djnz]

Some hot air stations use a reed switch + magnet combination to do essentially this. Quite robust, I think, and also super easy to hack together.

[mstoer]

I have the same iron.  The "springy" holder does not flex much at all, not enough to activate a lever switch anyway.  The IR beam might work fine.   What about an optical proximity sensor aimed near the handle (at the shiny metal portion)? Something like this (I happen to have some lying around):  http://www.mouser.com/ProductDetail/Optek-TT-Electronics/OPB701/?qs=iblIa22dKKSWTrqmEvNb1g%3D%3D

Edited to add:
I just mocked it up quick with the OPB701 I had and it works fine.  It has a detection range of about 1" (25mm).   I would just need to find a way to mount it so nothing gets too hot.

[vealmike]

Springy metal holder?
Solder iron tip connected to Ground (mains earth)?

cmon.

[cverburgh]

Wow, lots of ideas! Thanks for your help. Here's a picture of what I have so far for sucking the air away.

I used the existing AC wiring that was attached to the light bulb. I cut off the plug that goes into the wall and soldered on some 4mm bullet connectors.

I should have some time tonight to try out the IR setup. I'll do some research on the other ideas, but I want to keep it as simple, neat, and clean as possible, so the fewer the components the better.

I also included a photo of a solder spool holder I created, just for fun. I'm not totally happy with this yet, I think I can simplify it without decreasing the structural strength.

[cverburgh]

To answer some of the other questions:

how long do you solder at one given time? A simple foot switch would work if it is not an hour or more it wouldn't be too tedious and you could press with your foot at will.

I will often sit at the desk for an hour or two with the iron on. It will be out of the holder usually 10-20 seconds at a time. I'm usually soldering just 1-3 points at a given time before I put it back in the holder to check my work.

How hot does it get right at the opening of the stand, closest to the handle? You could mount a button there that has a spring loaded piece of tin bent to release the switch when the handle of the iron rests in the holder.

I don't know exactly how hot it gets, I don't have anything to measure it with. I'll check it tonight by touching it as it heats up to get a rough idea if I think it would melt or deform plastic. I have a small micro-switch so I'll play around with it for some ideas.

You can put a pair of metal contacts on the holder. When the iron is in place it makes contact and an AC detect current passes (AC so it can penetrate oxides) and your circuit can take some measure against it.

Would the contacts be normally closed or open? Would the soldering iron break through those contacts, or simply sit between them to complete the circuit? I know nothing about how this would work, but it sounds like an interesting learning opportunity, even if I don't use it in this project.

Idle speculation: find out the idle heat cycling. When the iron is in use, I suppose it will be heating more often/longer than when sitting in the holder.

I though about this as well, there has to be some way within the iron base electronics to tap into the circuit to detect when the temperature is changing. I figure while in use, the temperature must me constantly fluctuating. It cools a bit when in use, then spikes back up immediately after pulling away from the work, then settles back down again to the idle temperature. I wonder if there's a schematic floating around somewhere for my iron.

[Fungus]

Idle speculation: find out the idle heat cycling. When the iron is in use, I suppose it will be heating more often/longer than when sitting in the holder.

Not necessarily. If it's touching the holder (eg. one of those 'spring' holders) then the holder could be absorbing a lot of heat.

I though about this as well, there has to be some way within the iron base electronics to tap into the circuit to detect when the temperature is changing. I figure while in use, the temperature must me constantly fluctuating. It cools a bit when in use, then spikes back up immediately after pulling away from the work, then settles back down again to the idle temperature. I wonder if there's a schematic floating around somewhere for my iron.

Is your iron thermostatically controlled? If not, maybe time to get one.

Thermostatically controlled irons heat up a lot faster because they have power to spare and pulse-heat the element after they get up to working temperature. Faster heating means you're more likely to switch it off when you're not using it - no annoying two minute wait.

If it's temperature controlled you can dial it down when you're not using it. Heating up from a 'standby temperature' only takes five seconds or so on a decent iron.

If it's not temperature controlled you could get a foot switch, that way you always remember to switch it off.  It'll take fifteen or twenty seconds to heat each time, but...

Ideal would be a combination of the two. Foot switch plus a standby temperature. I don't think they make those though. 

(or if they do make them they'll be expensive...)