Guide QT110 Touch-Sensitive Button Guide

TYVM!! Now I know exactly what additional stuff I need to order. But I may have to wait a few weeks cause now my laptop is overheating , and I must look into it. I am afraid the board is going out (no onboard temp sensor) because the fan is turning on, but it is still getting very warm in the fan area. Just having a rash supply of bad luck lately so if anyone needs some additional bad luck to give to a coworker just PM me

 

ya I meant the plain basic qt113 schematic. because no one can see it now.

anyways, thanks for the help you've given to us all!

 

Time to revive this old thread!

Need some help from you electrical smart people.


So ive made my regular circuits and they work great.

Now ive made my circuit for turning on and off my case lights. Circuit is put together correctly. When i touch it, the output of the chip sends a current. When I touch it again the current turns off.

Now ive got the output connected to the base of my transistor. 12V power connected to the collector and the ground connected to the emitter.

BUT!! it doesnt turn on my case lights. I have found the reason why though.

I have tested and when the circuit is off the voltage going to my lights is 0V like it should. But when turned on its only 4.8v when it should be 12V.

Why is this happening?? Is the transistor limiting my voltage or what?


Please help me. I cant figure it out. It should be working correctly.

 

What's the voltage/current coming out of the IC?

 

Here is a picture to show what is happening and how its hooked up.

 

What sort of transistor is that?

Unless you got active high version of the qt113, then the output will be 0v.

I think here you'd need a PNP or a mosfet.

 

Link to transistor datasheet

http://www.fairchildsemi.com/ds/TI/TIP121.pdf

The qt113 is supposed to output. It's on toggle mode. When you touch it, it turns on and outputs a signal. When you touch again it outputs nothing. And that is how it activates the transistor.

 

Ahh, i haven't tried toggle mode.

Well seeing that it's an NPN transistor, it all should work if you use the transistor to break the negative lead of the invertor, not the +12v lead. I'm not sure if an NPN transistor can be made to work the way you have it hooked up to break the +12v, but i've used them to break the -ve line and they work perfectly.

You should also fit a resistor in the line between the base and the QT113 output, around 5-10k ohm.

Keep an eye on heat generated by the transistor. If there is heat, then fit a small heatsink, like an old chipset heatsink or whatever. The rear metal tab seems to be isolated from the pins but i'd check with a multimeter just in case.

And i've got a few curious questions for you!
So what types of touch senor pads have you used? As in steel? Alloy? What thickness? What area & shape? Are you touching them directly or sensing through plastic, or other material? Pics of the setup? And what capacitance have you used for the sensitivity?

 

@ talladega: how close can you mount your sensors to each other without them interfering with each other?

 

This should work:

Note the changed wiring so that the negative lead is being switched by the transistor, and the collector & emiter connections are swapped. I've also chucked in the resistor, a 10k should be good.

You may notice heat after a while of the lamps running at the full 12v, but if even after an hour there is no heat, then all is good. If you did have to heatsink the transistor however, you can use a mica washer to insulate the heatsink.

Those washers are nice thick sensors. You total capacitance is still quite low at .055uf, so if you did decide to increase it's sensitivity, feel free to add another capacitor or two in parallel.

@Macros From the datasheet you can apparently mount the sensors within millimeters of each other, you just need an insulation earth in between them, such as a thick wire or a piece of insulated or at least securely separated conductive metal. This insulating earth acts like a faraday cage between the sensors.
I haven't tried it so i don't know how close you can go, but i think the thicker the metal sensors are, the thicker the insulation earth will need to be to shield the magnetic fields.

 

Cool! Thanx for the info! =D

 

Mine are about 1/8" or so apart from each other.

Insulate them? Hmm I havent done anything like that. Mine are all hot glued to some plastic. Is that insulating enough? They dont seem to be interfering.

 

Sweet, that's much closer than I will need. =D

@ everyone: have anyone had any experience with metal structures behind/arround the sensor producing interference? I'm planning place sensors within holes (a little bigger than the sensors) in alu sheet metal, and then cover em up with a thin acrylic sheet. Do you think I will get interference from the surrounding alu sheet??

 

I've no clue about interference. My case's frame is made of aluminum. They are also right beside my fan controller and card reader.

I guess with things like these the only way is to try it out.

Make sure you have extra material incase you have to redo them.

Also. get the ones that go in IC sockets. DO NOT get the super tiny ones that are mean to be surface mounted on a circuit board ( unless you have a circuit board I guess ). I got those and they are terrible hard to solder. The pinds are like 0.5mm away from each other. You need a VERY steady hand to do it. I bought extra because I knew I'd mess them up and I did. LOL

 

Well I tried that mvagusta and it doesnt work.

Now the lights just stay on all the time.

Not sure what to do now.

Maybe instead of a transistor and such just use a 5V > 12V converter and just send the signal from the qt113 directly to the inverter?

edit: found a converter. seems like it'd be good. http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail?name=102-1349-ND
only thing. how do i use it? I know how it would wire up, but do I need any other components as well?

 

It should work fine, check the "off" voltage coming from your QT (and all your connections). The reason your original circuit only gave 4.8V is you had the transistor connected as an voltage (emitter) follower on a 5V source.

 

Well now something weird is going on. The output of the QT113 is doing strange things. Now when its toggled on its only outputting 0.9V and when off it output 0.1V.

I have the 12V line going directly to the inverter, the GND from molex to the collector and then the wire from emitter goes to the inverter.


How does this transistor thing work? I dont understand why it was only sending 4.8V to the lights when I had 12V going into the transistor.

 

The NPN transistor is connected with the power leads the wrong way round. This usually breaks them.

http://forums.bit-tech.net/showpost.php?p=650633&postcount=6

 

so how i was doing it in this post was correct? http://forums.bit-tech.net/showpost.php?p=1824239&postcount=205

But how to make it so the emitter allows 12V output instead of 4.8V. I think I understand it is to do with the output of the QT113. I need to do something with that to make it work right? What makes it work?

Maybe diagram from you helps? That diagram in that post you linked to is too confusing. I dont understand those symbols and how its hooked up.

I tried interpreting that post and this is what I've come up with. Not sure if its right.




Edit: Just incase it makes a difference. These are TIP121 Transistors I'm using.