How to detect when soldering iron removed from holder - Page 1
Forum section: electronics / projects

author: cverburgh
author_rank: Contributor
timestamp: February 28, 2017, 07:07:09 pm
content: 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 WellerWESD51soldering 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?

author: cowana
author_rank: Frequent Contributor
timestamp: February 28, 2017, 07:09:36 pm
content: How about an IR beam across the inside of the holder, broken by the iron tip?

author: CJay
author_rank: Super Contributor
timestamp: February 28, 2017, 07:13:52 pm
content: 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

author: bji900
author_rank: Contributor
timestamp: February 28, 2017, 07:18:25 pm
content: 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.

author: tpowell1830
author_rank: Frequent Contributor
timestamp: February 28, 2017, 07:19:24 pm
content: 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!

author: SeanB
author_rank: Super Contributor
timestamp: February 28, 2017, 07:24:27 pm
content: 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.

author: KL27x
author_rank: Super Contributor
timestamp: February 28, 2017, 08:25:29 pm
content: Quote+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.

author: nali
author_rank: Frequent Contributor
timestamp: February 28, 2017, 08:31:09 pm
content: A thermister glued to the metal holder? Would give you a bit of an off-delay as a bonus

author: eugenenine
author_rank: Frequent Contributor
timestamp: February 28, 2017, 08:55:36 pm
content: 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.

author: cverburgh
author_rank: Contributor
timestamp: February 28, 2017, 08:59:38 pm
content: 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.

author: tpowell1830
author_rank: Frequent Contributor
timestamp: February 28, 2017, 09:05:36 pm
content: 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.

author: PCChazter
author_rank: Contributor
timestamp: February 28, 2017, 11:56:54 pm
content: 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

author: technix
author_rank: Super Contributor
timestamp: March 01, 2017, 09:11:05 am
content: 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.

author: TiN
author_rank: Super Contributor
timestamp: March 01, 2017, 11:54:37 am
content: ERSA using accelerometer in handpiece for that in ICON series

author: mikerj
author_rank: Super Contributor
timestamp: March 01, 2017, 03:36:36 pm
content: 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.

author: bji900
author_rank: Contributor
timestamp: March 01, 2017, 03:40:27 pm
content: Vision System connected to a PLC to start and stop the system. Should not be too hard...

author: nanofrog
author_rank: Super Contributor
timestamp: March 01, 2017, 11:57:10 pm
content: Quote from: eugenenine on February 28, 2017, 08:55:36 pmMy Weller WD setup does it this way as well.Some of the newer series' of tools however, utilize an accelerometer.

author: Alex Eisenhut
author_rank: Super Contributor
timestamp: March 02, 2017, 12:28:55 am
content: 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.

author: eugenenine
author_rank: Frequent Contributor
timestamp: March 02, 2017, 01:22:58 am
content: Quote from: nanofrog on March 01, 2017, 11:57:10 pmWhy just use a simple switch when you can over engineer it rightMaybe newer irons can pair with your phone and tell you if your holding it wrong

author: djnz
author_rank: Regular Contributor
timestamp: March 02, 2017, 03:20:27 am
content: 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.

author: mstoer
author_rank: Contributor
timestamp: March 02, 2017, 05:19:56 am
content: 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%3DEdited 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.

author: vealmike
author_rank: Regular Contributor
timestamp: March 02, 2017, 09:15:49 am
content: Springy metal holder?Solder iron tip connected to Ground (mains earth)?cmon.

author: cverburgh
author_rank: Contributor
timestamp: March 02, 2017, 01:26:07 pm
content: 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.

author: cverburgh
author_rank: Contributor
timestamp: March 02, 2017, 01:42:02 pm
content: To answer some of the other questions:QuoteI 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.QuoteI 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.QuoteWould 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.QuoteI 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.

author: Fungus
author_rank: Super Contributor
timestamp: March 02, 2017, 04:04:21 pm
content: QuoteNot necessarily. If it's touching the holder (eg. one of those 'spring' holders) then the holder could be absorbing a lot of heat.Quote from: cverburgh on March 02, 2017, 01:42:02 pmIs 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 theydomake them they'll be expensive...)

author: eugenenine
author_rank: Frequent Contributor
timestamp: March 02, 2017, 04:33:07 pm
content: That was the big feature that upsold me to the Hakko 951 over the 888, the sleep mode (other was the temp sensor is in the tip). If I set the iron down and get lost in a forum thread for an hour then the iron has went to sleep.The spring iron holder doesn't flex, its mounted solidly to a panel which is hinged so that that panel can move slightly then had a spring holding it off of the switch.That lamp turned fan extractor, you could stick an LED light in the middle or ring around the outside so it can still function as a light.

author: nanofrog
author_rank: Super Contributor
timestamp: March 02, 2017, 06:19:05 pm
content: Quote from: eugenenine on March 02, 2017, 04:33:07 pmYou could use anLEDor evenfluorescentmicroscope light for this.

author: rancor
author_rank: Contributor
timestamp: March 02, 2017, 06:32:05 pm
content: I think the WESD51 has a grounded tip. The holder is metal so could you just check to see if the holder is grounded?

author: cverburgh
author_rank: Contributor
timestamp: March 03, 2017, 01:12:50 am
content: So, the stand is too stiff to make it practical to use a micro-switch with it. The piece that the soldering iron fits into is ceramic, insulating the iron from the holder, so even if the iron was grounded there's no way for me to check that other than connecting to the iron itself.I hooked up a photoresistor/photocell/light dependent resistor and that seemed to work pretty well (photos attached below). With the iron in the holder, and the holder in it's normal place, there's about 120k-170K? resistance through it. when I remove the iron it sits around 6K-8K?. I left the iron on at 500F for about 10 minutes. The ceramic part that it goes into was still cool enough that I could hod onto to. It was very warm, but not too hot to touch or hold for an extended time.I think it would be safe to say that if there is less than 10K? resistance the fume fans should turn on. It's a fairly clean install requiring just two wires at the iron.Now it's time to figure out the circuit. This is new to me, as I've never had to come up with a circuit from scratch. It should be a great learning experience trying to figure it out. I'm sure a lot of you will know exactly what to do, but I would appreciate it if you didn't post a solution, I want to try to figure this out on my own. However, if you don't think this is the way I should go, I would appreciate feedback on that!Regarding the question about adding a light inside the fan shroud, I thought about that, but I'm worried that it will shine in my eyes and be distracting. I bought two of those lamps, one to use as a fume fan and the other to use as an actual light. I'm going to leave it as-is for now just to see how things go. It should be pretty easy to add LEDs anytime in the future.Thanks

author: cverburgh
author_rank: Contributor
timestamp: March 04, 2017, 03:44:52 am
content: Ok, so I got it working!My BOM:(1) L7805CV 5V Regulator(1) ST TIP120 Darlington Transistor.Datasheet found here.(1) 680? Resistor(1) Photoresistor(1) 12V, 3.3A Power source(2) 12V Brushless fans from an old IBM server(1)Ikea desk lampLucky for me, the only thing I had to buy was the lamp, I had everything else sitting around.The TIP120 that I have has gain (Hfe) of 1000, which seems a little low compared to some others that I've seen which were around 2500.Anyways, from the 12v power source I take the positive line and go through the 5V regulator, then through the photoresistor, then through the 680? resistor, then to the base of the TIP120 darlington.The TIP120 emitter is tied to ground and the collector goes to the negative side of the fans.The positive side of the fans goes directly to the +12V source.Here are some measurements I took:PSUNo load: 12.3VWith fans running: 11.76VMy DMM can't measure current anymore, I fried that a while ago, but when hooked up to my bench power supply, set at 12v, the fans pull about 450mA each, about 980mA with two hooked in parallel. When powering on, I can't tel for sure, but I think it goes up to somewhere around 2A. I can see the power supply current reading heat about 1.7-1.8A for a second, but I don't consider that a reliable reading. The supply peaks at 3A, and it doesn't trip that with the current adjuster set to about 2/3 of max.Output from TIP120 going to fansWith fans disconnected, iron removed: 12.26VWith fans connected and running, iron removed: 10.65VWith fans connected, iron in the holder: 0.4 - 0.6VIf I put my desk lamp directly over the iron when it's in the holder, the TIP120 output is around 2V, +/-0.5.The 5V regulator holds rock solid at 5V regardless of what else is going on in the circuit.As per the datasheet, the ST TIP120 has a built in diode. Is this sufficient to protect the circuit running these fans, or should I add an additional diode between the collector and emitter?I'm printing the mount for the photoresistor, I'll post some pics as soon as all the fine-tuning is completed.

author: Alex Eisenhut
author_rank: Super Contributor
timestamp: March 04, 2017, 03:58:04 am
content: Weigh the holder?

author: cverburgh
author_rank: Contributor
timestamp: March 04, 2017, 04:52:09 am
content: No need to weight the holder. I 3D printed a holder that holds the photoresistor under the handle of the iron. The foam part of the handle rests ever-so-gently on it covering it completely. The setup is almost done. I'll take some pics tomorrow or Sunday, time for bed now!

author: Ian.M
author_rank: Super Contributor
timestamp: March 04, 2017, 05:19:07 am
content: That's fugly, and I'd bet the 3D printed holder wont like how hot the stand can get.Detecting the grounded barrel in the holder would be preferable. A metal contact sleeve inside the ceramic insulator, formed from tin-plate cut from a can, retained by three tabs bent out either side with a long lug for a female spade crimp terminal, extending up between the coils of the spring, insulated with fibreglass sleeving, and bent back 90° at the end, connected to a heat resistant wire led back along the support rod would do the trick.See attached schematic for suggested circuit. The ground return for the 'switch' would be va the soldering station to mains earth, hence the slightly complex base circuit designed to stand-off a bit of mains hum, with C1 to filter out EMI picked up on the wiring while the iron is out of the holder.

author: cverburgh
author_rank: Contributor
timestamp: March 04, 2017, 07:06:22 pm
content: Quote from: Ian.M on March 04, 2017, 05:19:07 amThanks, I appreciate that. What you see above was a prototype, just to see if it would work. I have attached completed photos below.I made the 3D printed part so that it can be tightened, so hopefully it won't deflect too much, but only time will tell. There really isn't any strain on it other than the weight of the sensor. The ring is sandwiched between the ceramic holder and the spring. If it fails I can always print another. The iron is rarely on for more than an hour or two at a time.I want to keep this simple with as few parts as possible.I put the circuitry in a little project box and also added some LEDs. The yellow one comes on when the box has power, and the green one comes on when the iron is removed from the holder and the fans are (or should be) active. The fans are attached with a pair of 4mm banana plugs, and the sensor is plugged in with a little 2-wire JST plug.The only thing left is to add a 2.5mm power plug receptacle and a switch, and find an appropriate place to put it.

author: SeanB
author_rank: Super Contributor
timestamp: March 05, 2017, 07:01:18 am
content: With the extractor, I would suggest 3d printing a small extension tube to place between the fans, so that the airflow from the one fan is not obstructed by the airflow turbulence around the fan mountings. This should make them a little quieter in operation, though you can also place a small printed vane set inside to straighten the airflow as well, keeping it laminar to reduce noise, but the tube will need to be longer though. Just a 1in tube will make a difference, especially if you make it to the outer dimensions of the fans and put the screw mounts into the end, making a small muffler.

author: cverburgh
author_rank: Contributor
timestamp: March 06, 2017, 05:33:33 pm
content: Hi SeanB. Thanks for your input, I will give it a try.I'll do up a design this week some time and post it here to make sure I'm understanding you correctly.

author: cverburgh
author_rank: Contributor
timestamp: March 14, 2017, 12:43:52 am
content: Hey SeanB,I made up a model and put it on Thinigverse athttp://www.thingiverse.com/thing:2175262Is this what you were talking about? The height is 27mm, a little over an inch.Craig

author: Richard Crowley
author_rank: Super Contributor
timestamp: March 14, 2017, 01:10:48 am
content: Don't many modern irons have this feature built-in to the handle?Not a week ago I watched a YouTube video about a Hakko clone kit which included a "vibration switch" in the handle.It is used to "wake up" the iron from "idle" when the user picks it up out of the stand.

author: tooki
author_rank: Super Contributor
timestamp: March 14, 2017, 10:44:45 am
content: Quote from: Alex Eisenhut on March 02, 2017, 12:28:55 amFWIW, my Ersa i-Con Nano uses a variant of this for waking from setback (200C): it detects the temperature plunge from putting the tip into the brass wool, and wakes it back to the set temp, which takes only around 4 secs. This model uses a rubber and ceramic iron stand, so the tip is always dangling midair and has no metal parts to touch.(What's annoying is that later on, when it goes from 200C setback to 50C sleep mode, it is expecting a quick drop, so doesn't detect the brass wool. So if I try to solder right after it's decided to sleep, i have to wake it up with a button press. The bigger models use an accelerometer in the handle instead.)

author: cverburgh
author_rank: Contributor
timestamp: March 14, 2017, 12:01:50 pm
content: No, as far as I can tell there are no motion sensors of any kind in the handle.The setup I have now is working perfect. It's not the most elegant but it's simple and it just works.So far the 3D printed ring around the ceramic holder that holds the iron is holding up perfect.