when building arcade sticks common ground game pads are used for several reasons. One reason is to build up dual PCB in one arcade stick. Due to this for example PS2 and xbox360 can be connected to the stick. Next reason to use common ground pads is to connect common ground joysticks like seimitsu LS32-01 and Sanwa JLF sticks. These use common ground pcb interfaces. Also UPCB needs xbox360 common ground pads for piggyback.
Since there nearly exists no more common ground pads in europe I've found a solution to make out of non common ground pads common ground ones. In the prior post I've shown a scetch. No I soldiered a prototype on breadboard. The solution is cheap and needs only few part. Per signal you need one optocoppler and one resistor, thats all.
I'm using in the pics 1k ohm resistors and 4N 27 Optocopplers .
Here's the padhack connected to the optocopplers on the bread board. Every pad has two wires to the optocoppler ICs. Pad used is Big Ben xbox360 game pad.
Close-up: The thick wires goes to a seimitsu LS32-01 Stick which is common ground.
Yeah, it works fine :-)
Pin1 -> resistor 1k Ohm -> 5V USB
Pin 2 -> Signal Arcade Stick, i.E. Direction Down
Pin3 -> Not Connected
Pin4 -> GND line from gamepad for direction down
Pin 5 -> Signal line from gamepad for direction down
Pin 6 -> Not Connected