Guide QT110 Touch-Sensitive Button Guide

It is so wrong. TIP121 is an NPN power darlington, the 'emitter' lead has the arrow pointing in the direction of conventional current flow (positive to negative) on the symbol.

• +12V to load positive ("Load" is your inverter)
• Load negative to collector
• Emitter to ground (0V)
• Base to resistor to QT113 output. Resistor can be any value 1k-10k

 

I think I have finally grasped it ( and fried a transistor and qt113 in the process )

Is this correct?





Edit: looks like the one mvagusta posted above was correct all along? I must have done it wrong.

 

Havent tried this but I think I fried this QT113 I was using. I need one more now.

Anyone in U.S. or Canada got a few spare QT113 chips I could buy? Digikey is out of stock unless I buy over 3000 of them. Only need a few so ordering from Newark or Farnells is pointless.

 

Sorry i didn't see this earlier. I would have told you to double check all your connections if i saw this thread when you said my circuit wasn't working. I loled when i saw that second last complex wiring diagram on the previous page! It looks like a flux capacitor for a time machine or something like that

But hey, don't worry, you've learnt more about electronics just as i do among other things from this forum, so don't think of the blown parts as wasted money

 

well im not 100% sure its wrecked. i havent tested it yet. but for some reason 12v was going out the output of the qt113 and ten i got really hot so i unplugged it all.

it wasnt for very long so maybe after being cooled down and resets it'll work.

otherwise im gonna have to spend like $30 to buy a $3 chip.

So that last picture I made is what will work?

 

Your picture is the same as mine, just make sure the resistor is connected to the base, and that the emitter goes to the earth at the molex, not the other way round.

Don't be surprised if the QT113 is blown though. There must be other places you can order it from, or maybe you can do a group buy with a few mates? Or maybe you can just buy the $30 worth of chips, make them all and then sell them to mates

 

I forget all the differences but QT110DG in stock at Futurlec, $3.20 each and fairly cheap shipping everywhere.

 

Thanks. I actually found a place that sells them in US and Im getting a shipping quote right now.


Anyways, I soldered up a new chip. Before hooking up transistor i made sure it was working correctly and it was. So then I finished it up and it still is not working.

Here is a picture showing how I have it done and I put numbers where I tested the voltage and then made a chart that shows what the voltage is when the QT113 is toggled on and off. Hopefully you can help me fix it with this information.



Just incase it makes a difference I have this thing hooked up to two light inverters to power 4 lights. One of the inverters is actually fried right now so I only have one of the plugs plugged into an inverter. Not sure if it makes a difference or not. I need to order new set of lights.

 

It should be working perfectly!

Lets take the QT113 out of the equation, try just connecting that resistor to 5v, instead of the QT113.
So in other words, the base of the tip121 goes to the resistor, and the other end of the resistor connects to 5v from any of the molexes.

If this doesn't work, check to see if the resistor is actually giving 10k ohms resistance, as maybe it is dead/open circuit?
If the resistor is good, your connections are all good, then we know something is wrong with your tip121.

And also, before any of this, just in case you haven't tried, connect the invertor directly to 12v and see if the invertor actually works at powering up your lights?

 

Resistor shows up as 9.75K so that's all good.

The inverter does work. I just confirmed it (and confirmed the other one is dead). I hooked it up the way I have it and just connected the collector and emitter together and the lights turned on.

Now some things confuse me. When I actually have it plugged into the inverter I get much different readings.

On the QT113 side of the resistor its still the same 0V-off and 4.9V-on which means its working perfectly, but on the other side of the resistor at the base of the TIP121 I'm getting voltages of 7.XXV-off and 9.XXV-on. And the collector is showing like 11.2V.

Should it not be that the collector show -12V? And when the QT113 is toggled on the emitter show -12V?

in the datasheet for the TIP121 it has this sample circuit shown.



Maybe what I've done isn't correct way of wiring it?

 

The 11.2v is probably about right as there is around .7v drop from the tip121.

Maybe you should post a couple of pics, as maybe you have something wrong in the wiring?

I don't know how the emitter can show 12v as it's supposed to be shorted to earth. It shouldn't ever be anything other than 0v.

 

Everything seems to be dont correctly though. When I put a wire across the collector and emitter so they connect the lights turn on. Could it be that the collector and emitter should be swapped around?

I'll see if I can get some pics. Not sure how helpful they be.

 

Ok, here is some pictures. Dont laugh too much!

Hope it helps.....

 

There's a fault somewhere, the voltages around the darlington switching transistor should be very close to these when it's on. When 'off' the 815mV on the collector will become 12V, the 1.41V at the base will become 0V. The emitter is always 0V.



R6 is a 2A load (in your case, inverters).

 

I think everything is hooked up correctly.

For some reason though its not turning on. The QT113 is outputting the correct signal. That is all good. But for some reason the voltage is HIGHER after the resistor. When i test it on the QT113 side of the resistor it changes between 0V and 4.9V like it should. But when I test it at the Base of the transistor it shows around 9V or so. To me it seems like the transistor is sending some of the voltage from the collector to the base for some reason and that is not allowing the current from the QT113 turn on the transistor.

I will try another transistor and see what it does. Maybe I wrecked this one somehow.

Maybe I need a resistor somewhere else too? like at the collector maybe?


BTW, Like my fancy circuit board?





EDIT:::::::: It works!!!!!!!!!!!! I swapped out the transistor with another one I had and now it works perfecto!!!!!

Thanks for the help guys!!!!!!!!!!!!!!!!

 

Thank god, as all i could do is play snakes and ladders. Your circuit board is Cheesecake

 

Tomorrow I will add a little more hot glue to secure everything now that ive got it working. Next up, eject switches for dvd burners and then wire up my LEDs. ( I dont think I will have any trouble with that. )

 

Oh yeah, so the tip121 doesn't get warm driving the invertors? Just be aware that if you cover the tab with hot glue it will increase temps. You can make them secure enough by just hot gluing the legs, and yes, even the legs act like little heatsinks so even covering them can increase temps a touch. But maybe even after an hour or more there is no heat to worry about?

And with hooking up leds, do you mean hooking them up to the QT113 output, to indicate when the touch sensor is being triggered? If so, i think the limit for the QT113 output was 20ma, so if i was gonna hook up an led directly, i wouldn't go over 10ma, to prolong the life of the QT113.

 

No it didnt seem to get warm. It's rated for 5A and the inverters only require 0.5A each.


The leds are going to powered by the 12V line so they are on all the time. Just the led for the power switch is powered by the PSU +5vsb line so the light is on even when the pc is off. All the other leds turn on when the pc turns on and then there is also the hdd activity led. All of them are red.

 

QT113/118

Obsoleted Parts Notification

You have purchased the following part number(s) from Digi-Key within the last two years. The manufacturer has announced this part(s) will become obsolete. Please click on the link below for more information on possible substitutes.

Manufacturer Details
ATMEL/QUANTUM Description: IC SENSOR TOUCH/PROX 1CHAN 8DIP
Manufacturer Part Number: QT113-DG
Digi-Key Part Number: 427-1095-ND


ATMEL/QUANTUM Description: IC SENSOR TOUCH/PROX 1CHAN 8DIP
Manufacturer Part Number: QT118H-DG
Digi-Key Part Number: 427-1098-ND
Customer Reference Number: ACTIVE HIGH