Electronics QT110 Computer Power Switch (again, sorry guys)

Hi all,

Didn't want a whole new thread for this same topic, so I'm bumping this thread. Can I get a check on this?

I also want to create a touch-sensitive power button and have been looking into the QTouch ICs. Disclaimer: I've never used a soldering iron, and I only have basic E&M knowledge, so bear with me.

The sensor will be behind 1/8" smoked plexi, and will be made of metal screen-door mesh -- I read that this will work well. The power LED will be behind this mesh to backlight the button.

As for the QT110 circuit, this is what I have as my diagram per cpemma's (and other reading I've done) diagram above:



The inevitable questions:

1. Just to make sure I've got this straight, VDD on the QT110 is tied to Pin 9 (+5VSB) on the PSU's ATX connector because it's the only line that will have power while the computer is off, right? Otherwise for a non-power button (say, transport controls like Play, Pause, etc.) I'd be able to use any +5V line?

2. What's the best way to tie VDD to +5VSB? My thoughts are to remove the pin from the ATX connector, strip the sheath a bit, solder a wire going to VDD, heatshrink the lot of it and put the pin back into the connector. Am I on the right track?

3. Per the QT110 datasheet, nstead of (or in combination with) Cs, I can use a piezo sounder with 3.5-4.5kHz peak acoustic output. I'd like to have the acoustic drive provide feedback (like a beep) when the button is pressed, so I'm looking into using a Panasonic EAF-12RF04C speaker:

LINK: Digikey catalog page, see bottom

4. I see in the photo of cpemma's circuit a few resistors. I don't see any in the circuit diagram. Are those for a separate circuit, or did I miss something?

5. Should I use some type of shielded wire to avoid interference that will trigger false detections? In fact... what kind of wire should be used for any type of circuit/electronic work?

6. Am I supposed to use the QT110-D, or the QT110H-D?

I know, lots of questions... I have done a lot of searching and reading, but I'm still a little confused, so if anyone can point me in the right direction, I'd be much obliged.

TIA

 

A lot of modern mobos have some headers with +5vsb (and a ground). Mine has a case-intrusion one and an IR module one available, RTFM, YMMV.

 

I have an Intel D875PBZ. There's a +5V DC pin on the front panel connector but I've been searching Intel support documents for a week to find out if this is a +5VSB connection or not.

There is a chassis-intrusion connector, pin 1 = INTRUDER and pin 2 = GROUND. I guess I'll have to take a multimeter to this and see what I get when the power's off and chassis intrusion detection is set to "Off" in the BIOS.

Serious dearth of information on this chez Intel.

 

1. Yes.
2. Look for a Wake-on-LAN header, that should definitely have a +5vSB line.
3. I see no problem with that.
4. I believe you meant in coorz's picture. Looks like the other stuff is for the switching circuit.
5. One of those things where you'd probably have to put it together and see.
6. An earlier post of mine in this thread states the difference. You want the non-H version, because grounding the FPBUT_IN terminal will turn the computer on.

 

Oops, yeah, that was coorz's picture.

Thanks for the info, that'll help plenty. I think I'll just order a bunch of these, try a bunch of stuff, and post my results.

 

Is it possible to wire one to turn on and another to turn off?

 

Ok, I know very little about electronics, but am capable of basic soldering etc. I have a question about the QT110 (I understand how to set one up to act as a powerswitch etc, but don't get the feedback stuff in the spec sheet).

So my question is, is it possible to set one of these up so that touching the surface actually triggers the power on/off but proximity to the switch triggers an led? If this is possible, how?

This would let you do something cool like 'invisible' buttons that light up when your finger passes over them, and trigger their function when you touch the plate. I can see how you could theoretically do this with two of them close together, but one with a higher sensitivity than the other (effectively 2 distinct switches, though configuring the distinct sensor plates and still letting the led light through would be interesting), but is it possible with one qt110?

 

Don't see why but you can build two same circuits parallel, so basically they are both on/off switches.

Sweet idea! I think a single QT110 and a PIC should be able to take care of that.

 

Hehe well, if it requires programming a PIC I'm SOL as that's way over my head (let me rephrase that, I don't have time to learn it...).

I wonder if you could do this with a metal washer for one sensor with a plexi rod inside that, then a metal rod as a second sensor inside the plexi rod... wire the first qt110/washer sensor with a 20nF or 30nF cap to light the led (which would light the plexi rod) and the second qt110/rod sensor to a 10nF cap to actually trigger the power/dvd/whatever...

The only thing I'm not sure of is if the two sensors would interfere with each other. If they don't then the stronger field would trigger the led before you got close enough to actually trigger the button function. Another big question would be how much more sesitive the 20nF cap and washer would be... triggering at an inch or two would be cool, several feet not so much so

I'm playing with this idea for behind a smoked plexi faceplate. I want to figure out if I can do this before I really get started as I want the plate to be 99% blank (only marking will be icons over activity lights).

 

I think it would be unpractial to have a single button light up, that means you'll have hover your finger above the button to make it light up.
Sweeter would be if you make a larger proximity sensor that sequentially lights up al buttons when your hands approach the buttons.
This gave me an idea to make a child-proof powerswitch; sensors invisible behind black plexi

 

That's the effect I'm going for... invisible until your finger gets near it

It's also worth noting that there are probably only going to be 3 or maybe 4 buttons (power, reset, media eject, and maybe a light on/off if I decide to do an underglow effect).

I guess I'll need to order the parts and play around and see if it works... fortunately everything needed is cheap. I know the QT110 is supposed to compensate for other nearby sensors, guess we'll see how good it is. Time to go put together a Digikey order and get some plexi

Unless the child reaches out to touch the pretty lights

 

Cap part #s

Ok, anyone want to give me part numbers of 10/20/30nF caps they've used with these? Digikey's site is making my head hurt

 

Nevermind, found 10nF, 22nF, and 33nF 50V caps on Digikey, finally. Their site is just rediculously painful to use.

 

Agreed. Bumping this thread for a couple of (likely stupid) questions.

First off, I'm not sure if the 10nF caps I ordered (Digikey p/n P3848-ND) are suitable -- they're polypropylene film, unpolarized. Does this matter, or do I need to use polarized caps?

Secondly, what I'd like is to have an LED illuminated behind the touch button while the switch is inactive. According to the spec sheet, this requires that I connect the LED from OUT (pin 2) to Vss (pin 8). However, OUT is also supposed to go to the motherboard header. Can I split the connection from OUT, with one branch going to the motherboard, and put the LED (in series with an appropriate resistor, of course) on the other branch connecting back to GND? Will this affect the operation of the switch?




Thanks!

 

Thats how I have it wired (with the led) and it hasn't caused me any problems.

I'm also using an unpolarized cap and it has worked fine for me. Generally speaking, if the schematic uses the |( symbol for the cap, you don't need polarized. The polarized symbol is |(+ if I remember correctly.

 

Thanks!

I'm going to try the circuit with the unpolarized cap and I'm also going to see what happens if I replace Cs with a micro piezo sounder, per QProx's QT110 datasheet (and per my first post in this thread (#21). I found one at Digikey within the required peak acoustic range and with a capacitance of 10nF, so it should work just fine. I think the part number is P9910-ND.

 

The only reason AFAIK for polarised (electrolytic) caps is to get a high value in a small and cheap package. An non-polarised is generally better - tighter spec, lower leakage, works on AC.

Watch the QT110 spec if you're using LEDs. Can only source 1mA, sink 5mA.

 

Yep, I recall reading those source/sink numbers in the datasheet.

To verify, this means the IC can provide 1mA of current, and handle an input of 5mA, right?

I have a couple of yellow LEDs with a forward current rating of 2mA (as well as some of the more "standard" 20mA in other colours). Would it be better to use the lower-current LEDs?

 

That's it. If you ever need to, you can boost the load current with a small transistor switch, coupling the QT output pin to the base lead with a resistor to limit the QT current. So with a typical small transistor gain of 100+, that 1mA/5mA can turn on a lot more current.

Any modern led will glow quite well enough for an indicator on only 1mA, even if the spec shows numbers around 20-25mA for the rated brightness. Try yours on a 5V supply with some high-value resistors, see how the different leds perform.

 

Progress report, just to check my figures:

I've built the circuit as per my above schematic. I have it running off a spare molex connector but have connected neither the electrode nor the motherboard header -- I've got a stretch of connecting wire attached to those terminals instead.

The LED is on unless I touch the "electrode", which is great. Working like a charm there.

I've tied the IC OUT terminal to my multimeter's positive lead and have the meter's negative lead on ground. It reads +3.93VDC unless I touch the electrode wire, which makes it drop to 0V -- again, great.

My only concern is that normally, the FP_BUT header on the motherboard is receiving +5VDC from the PSU, right? Will the fact that it's only receiving ~4V through this circuit be a problem? My gut says no, as it only is triggered when the pin is grounded, but I want to check with other members' experiences.

TIA!