How to detect when soldering iron removed from holder

[eugenenine]

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.

[nanofrog]

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.

You could use an LED or even fluorescent microscope light for this. 

[rancor]

I think the WESD51 has a grounded tip. The holder is metal so could you just check to see if the holder is grounded?

[cverburgh]

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

[cverburgh]

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 lamp

Lucky 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:
PSU
No load: 12.3V
With fans running: 11.76V

My 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 fans
With fans disconnected, iron removed: 12.26V
With fans connected and running, iron removed: 10.65V
With fans connected, iron in the holder: 0.4 - 0.6V
If 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.

[Alex Eisenhut]

Weigh the holder?

[cverburgh]

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!

[Ian.M]

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.

[cverburgh]

That's fugly, and I'd bet the 3D printed holder wont like how hot the stand can get.

Thanks, 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.

[SeanB]

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.

[cverburgh]

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.

[cverburgh]

Hey SeanB,

I made up a model and put it on Thinigverse at http://www.thingiverse.com/thing:2175262

Is this what you were talking about? The height is 27mm, a little over an inch.

Craig

[Richard Crowley]

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.

[tooki]

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.

FWIW, 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.)

[cverburgh]

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.