I have been working on this project for a custom guitar hero controller for myself. For the 5 buttons on the frets I am trying to use a "finger touch activated switch" which I got from here http://www.discovercircuits.com/PDF-FILES/fingersw.pdf I have the parts and tested it with my power suppy and a LED and it works exactly how I want it to. But when I am trying to connect it to the circuit board taken out of a playstation controller is where I am getting stuck at. The circuit on the controller uses 5 wires all having 3.4VDC and then the common GND. So when the you want the certain button pushed the 3.4volts touches to the GND and the game see's that button is pushed. I've tried the finger activated switch and it will work at 3.4volts but how can I connect it to work with the controller circuit???
Thanks

 

Anybody have any ideas???

What I was thinking is there a circuit that when it gets voltage from my finger activated switch that it will switch to GND instead of the 3.4 volts.
Any help or advice would be appriciated.

 

You're going to need to find out where the Vcc/Vdd source is on the circuit board.

Right now, all you have is 5 control wires and the common ground.
You need an additional power source to pull the gate of each MOSFET up to around 3.5v to turn it ON to pull the corresponding control wire to ground.
The controller must have a Vcc/Vdd source somewhere.

 

I've got the power coming in on the circuit board I can use to power the MOSFET but the output of that would be 3.5V and then to connect that output to each of the 5 wires it needs to be switched to GND. I pluged the controller board in and used the multimeter and you have measuring from the GND to each of the buttons is 3.4V so when a button is pushed the GND is connecting to 3.5V.

 

So, since you have the circuit already, you know where you can get 3.5v, and you know that when the MOSFET's gate gets up over a volt (or so) relative to it's source terminal, that it's drain is connected to the source, right?

So, try just one channel first. Connect the source of one of your MOSFETs to GND, and the drain to one of the control wires. Use your Vcc/Vdd supply as the voltage source to bring the gate high.

Or are you still confused?

 

Yeah I'm still confussed. Here is what I'v got

The top 7 wires are coming from the console, I can take the +3.4volts from there to power the MOSFET. The grey wires at the right of the board are the buttons, when the board is on all of those measure 3.4volts.

 

OK.

The lines that respond to being shorted to ground (on the right, the "grey wires") are normally held to Vcc/Vdd via pull-up resistors.

You connect those lines (individually) to the drains of the individual MOSFETs.
You connect all of the MOSFET source terminals to GND.

You connect all of the 4.7M resistors from the gates to GND.

You connect the 47k resistors to your switch pad, which also has the +3.5v on the other side so that when your finger pad hits the switch, the gate is pulled high.

Are you still with me? Does this make sense?

 

Ok I think I understand now, I connected it up with my breadboard to an LED to test it. Only thing i noticed when testing was that the voltage was about 2 volts and not up 3.4 but I am going to fully hook it up to the controller and console and see if it fully works correct. Thanks!