Electronics QT110 Computer Power Switch (again, sorry guys)

Hi there,

alright don't blame me for posting another topic of this kind, I know there is a lot of those... I looked into cpemma's clear case computer - no schematic. Looked at coorz picture (http://www.xs4all.nl/~rccheng/bt/touch.jpg) - nice, but no schematic and works with a relay. Looked at several topics covering this topic - great texts, but no shematic because links were dead or topics too old. Read the whole datasheet - no powerup-schematic, that leads me to:

Guys I'd love to see a tutorial OR just a shematic how I should set up the qt110. It ain't that hard (I know that much) since I can just connect pins 3+4 to VDD which gives me the perfect DC OUT signal... but still I am confused how to hook it up to the power pins and to some molex plug.

So could anyone post a lil schematic here how to power up a computer with a qt110, I will post a tutorial then for later users so this question does not have to be raised every 2 days.

Thanks
voy

PS: I read several times, that the sensing field does HAVE to be dielectric. However the datasheet doesn't say so, it just says that it CAN be dielectric. Or does this have something to do with computer power up, because I can wreck something with that?

 

Well it's all in the manufactures spec. sheet. I edited a little:



This is how i use it for my Plexeon power switch. I can't remember though to which mobo header pin the output goes to, i think it was the positive header pin. But you don't need to worry, just try either one.

Image edited from original spec. sheet.

 

thx coorz, I remember that pic from the spec.

Where to put pin 8 (Vss). I mean it says ground in the spec, but I don't like connecting it to the case...

Besides that I think I can manage to built something like a switch.

 

Vss is just ground, any black wire from the PSU should do. Normally you'd tap into the +5 standby from the ATX, same for ground.

 

alright, got that I'm gonna try to built a switch like this tomorrow... maybe you could put that pic into the IC tutorial thread...

voy

 

What am I doing wrong?

Alright I have the lil circuit on a testboard, put in a 10nF Capacitor and, touching the "sensor-wire" makes my computer turn on.

great!

Now I want to use the dielectric material above the sensor wire, as stated in the datasheet or in bit-tech forums. My dielectric material is some plastic 1.6cm (0.6") thick. Beneath that I put a piece of alumunium foil to act as sensor.
To make it short: It doesn't work. Touching the foil does work!
So I thought to myself - "the capacitor must be too big, let's try a smaller one". Yeap, been there, done that. But still, I tried a 6,8nF, 4,7nF, 2nF... all the same outcome:
As soon as I connect the wire that powers up the computer, the computer turns on.
The only capacitor which gives me at least the chance to touch the wire is the 10nF.

How did you guys make your qt110 work? I must be doing something wrong, because the datasheet says that it's supposed to work behind dielectric material.

Additional Info: I got two wires acting as turn-on-switch for the PC. One is connected to the OUT Pin of the IC the other one is hanging loose, not connected to anything.

voystar

 

1.6cm is too thick, alu-foil is too thin i think. Try making a metal plate like this. With this sensor i get 4cm of detection.
Experiment with various shaped / perforated metal.

 

hmm... can't change the thinkness. I think I have to drill a tiny hole thru the plastic and put a lil wire in there. But I understood it right, that you're working with a 10nF too, right?

 

Yes mines a 10nF too. What do you mean you can't change thickness? Can't you replace the foil with a thin metal plate? Or a thin metal grid does wonders.

 

Oh yeah the foil can be replaced with everything, but still the diameter will stay the same, so does the plastic-knob.

Look I took out the original power swithc form my Chieftec case. The round hole is 0.7cm deep and 1.6cm in diameter (sorry so the plastic part is 0.7 cm thick not 1.6cm). So I made a little plastic knob out of plexi. Into that I drilled a lil hole for a 3mm LED and my plan was to cover the back of the knob with alumunium foil which was supposed to act as sensor.

Now using the 10nF resistor and just a thin wire: only TOUCHING does the powerup, promitiy is not enough

thin-wire + big piece of aluminium foil: same thing

all I gotta try now is if a thick metal plate 1.6 diameter will help to give me better results. Else I will just drill a 0.8 millimeter hole and run a thin wire thrugh there which you will barely see, but have to touch when touching the button.

 

That's normal. Proximity can only be attained by a good sensor design.
Indeed i think the small hole with a single strand of wire as sensor would do. Won't be proximity, but a nice touch switch then.

 

yeah gotcha, well anyhow that's good nuff for me. I'll get a shuttle soon anyhow, so the case will be trash at the end of the year :-D

 

I wired up this circuit like the picture above, but my sensor spits out 5V when I am NOT touching it, which makes it the inverse of what I need. Is there a way to set it to output 5V when touched? Did I get the wrong one (QT110) when I should have gotten the QT110H?

 

Yeah, you got the wrong one. The H version outputs a high signal (+5v) when the sensor is tripped, the other version outputs a low signal (ground).

Inverting it would be a simple enough.

 

Actually, I found I had a PNP transistor laying around, so I just used that. Hook the output to base and its all good.

 

Would've suggested that, but I figured there was less chance of you getting screwed over by following someone else's guide than to follow my advice.

 

Sorry my fault, forgot to mention mine's is based on the QT110H version .

 

your using a 10 cap try a 20 or 30 if i remember right it says use a 10 -40 cap. so my thinking goes as such. thicker material infront of the touch part = need more power to get through the thicker material

 

How can 1.6cm be too thick? QProx says they work with dielectric materials up to four inches thick.

 

The way they work is counter-intuitive, you increase the caps for more sensitivity, you can actually use up to .2 µf according to the spec sheet. I plan on using .1µf caps on a project I'm working on. If that is too much I'll just put the caps in series.