Hope you all don't mind a new thread on the Touch Sensors I've finally updated the project log with the schema for a power circuit based on the Qprox qt 118h (active high) touch sensor. Just triggers a relay (latch & hold) when the sensor it touched and releases when touched again. If your interested in the schema it's here Touch Sensor Power Circuit (Dont want to make the mod's angry! attaching as an image) As always ANY COMMENTS WELCOME!!!! Love to be able to post my project here but I've no host and these folk are kind enough to provide some limited storage... here's the project log ifin' your interested Project: Media 0n Demand
Good Catch Sorry! Yes the cap C5 was diagrammed incorrectly Fixed it in the schema... Thanks for the look see Cpemma!! C5 was the last component added to the circuit to smooth the output to the relay coil. The voltage is whatever your source voltage is less the loss across the darlington. The QT simply tickles the base. I had originally image tagged the graphic but as I mentioned I dont want to upset any mods so I figured a link be better if someone was really interested. Excellent point Cinnander diode clamp the relay!
You/anyone building this might want to also include a back-emf protection diode, all to easy to forget to add it externally! (for anyone wondering, you put a reverse biased diode across a relay or solenoid coil to dissipate the current induced by the B-Field collapsing when it is turned off) (oh and B-Field = magnetic field)
I thought this would be the right place to post, didn't want to start a new thread. Anyway I have a similar (more basic) circuit using the QT118H, I have set the IC itself working perfectly but I cant seem to get it to switch a Darlington? I'm hooking the output of the IC to the base of the TIP122 with a 2.2k resistor between. 12v is connected to the collector, when I touch the electrode the output of the QT goes to 5v, but when I probe the emitter of the darlington it also reads 5v? I don't get what I'm doing wrong. Any help is much appreciated. EDIT And I do have the QT setup to output in toggle mode BTW.
Limiting too much current to the base of the TIP??? Just a guess - your 2.2k is limiting too much current and wont fully switch on the TIP??? Just guessin' I've done similar switching 12v from the 118 and I'll have about 11.5+/- v at the emitter (marginal loss anyway) I use this circuit w/the 118 a LOT pin2 straight to base - 5v but little current.
Thanks for the reply HowY I've tried it with no resistor too and it still refuses to work, IDK maybe I've borked the darlington somehow, I'll redo the circuit with a new one and see if I can get it to work. I have got a QT113 to work for my DVD drive though, works most of the time. What is your electrode located behind and what is it made of? The circuit barely works behind a 3mm plexi panel that's with a 10nF cap and the gain set high (default).
Just shootin' darts in a fishbowl! The TIP you're using have a "saturation" spec? I'm no expert by any stretch so hopefully you'll get a reasonable answer that makes better sense.... I use a TIP122FS-nd (thats a digikey part #) the Vedo (base) saturation spec is 5volt - 5v turns it all the way up. post back what happens! EDIT: My "electrodes" are just 1/16" round steel wire inset into epoxy and covered with 1/4" ABS. Make a larger electrode or use denser metals if it's too sensitive add in a resistor twixt the electrode & the circuit - if it's not sensitive enough make the electrode larger / denser. Aluminum with it's relatively low K is a poor choice but a 1/4" copper slug is more sensitive than a 1/2" steel fender washer.... Just have to play around until you find the combination that works for the application at hand! Best of Luck!
Good news, I got it to work . I don't really know what was wrong I think it was a fried transistor. ( And I fried another when I was redoing it with a current overload, luckily I had a few more spares!) I'll have to experiment with the electrode a bit and see what works, but I'm happy for now.
PC Power Circuit For What it's Worth a circuit for a PC's power switch replacement MB Power Circuit If your considering the touch sensor for a PC (momentary) switch, be warned that the circuits powering the PC's header switch from pin 2 is delivering a steady 5v to the MB's header. (using active low IC) I just finished up a re-work of the "touch pc power switch" and was a bit surprised to realize that using the "active low 110/113 sensors" your really sending 5v to the header while the circuit is at rest. EESshhh! The touch power circuit is basically the same as this one - but using a switching NPN (base to pin2 on the 118h and emitter to ground (-coil-) and a rat shack micro relay. I don't know if it's within tolerance to run 5v down the header and it's just a few Ma's but I was not comfortable with sending voltage down the header and using a relay seemed the logical answer to separating the power header from the touch sensor circuit. Qprox Touch Sensor's Pin #2 Active HIGH - pin is 0v at rest 4.8+v when triggered Active LOW - pin is 5v at rest 0.6+v when triggered
