How to rig a capacitive touch to a usb keyboard (or gamepad)?

I need to make a touch sensitive (capacitive) button that triggers a key. I got a capacitive demo board from qprox that should be fine...I touch it and I can hook it up to an LED that gets lit. But if I try to put the wires from a button on a gamepad to the out of the demo board, the button is constantly in the "Down" state. I think I remember reading somewhere about a polarity reverser or something so that it reverses the On and Off state, but not sure what I need. Also, the demo board is powered via a small watch battery which is perhaps conflicting with the power from the USB? I'm not quite sure the best way to do this. I think I can power the demo board using the USB power rather than the battery. I also would like some advice on creating the Capacitor to a 3" button surface are that goes through 1/4" glass. I've got a resistor that upped the Qs so that it works through glass, but not sure how to make it fit to a desired "button" shape.

chipper356 years ago
Well, I think you answered your own question! I'm going to follow this, though, for my own knowledge!!
superjames (author) 8 years ago
I think I managed to figure this out. What I needed to switch the up/down state was a "Hex Inverter". Now the state is always up until I hit the capacitor. For now I laid out a bunch of pennies to create my capacitor and need to find a sheet of copper or something to replace them.
Photo 309.jpgPhoto 308.jpg
hiroe8 years ago
buttons are binary, it is probably analog. try hooking it up to a joystick.
superjames (author)  hiroe8 years ago
UPDATE: I got the power from USB working! I got the 3" capacitor working (using pennies hehe). So my problem still remaining is that the button is in the "Pressed State" until I touch my hand on my touch surface. I can get it to to be "Up", but then when I let go, it goes back down to the "Pressed state". So what I need to do is reverse it so that it's always Up, and when I hit the touch it goes Down. Thanks