Questions on hacking a USB pad

[Guywiththegun]

This isn't my primary strategy for getting arcade controls to work, but I had an old USB pad and some used arcade controls lying around, so I decided to try my hand at learning everything involved here. I got the PCB out, and it seems fairly simply. I have 100% no idea where the GND is of course, but I started testing some copper wire on the board to see what triggers what. I'm getting input in the PC for every button . . I initially thought I had found the GND but I'm getting input even when no wire is on a GND.

How and why is that possible? I thought you absolutely needed a GND wire connected to get input. Not only does it make it more confusing (not complaining, I know its a hack) but it makes me wonder if I wired my GND right in my IPAC! I mean would the IPAC work without the GND in and would that be dangerous??

Sorry if this sounds like I'm asking how to tie shoe-laces to some of you.

[boardjunkie]

USB pads may/may not use a common gnd for all the switch inputs. They are prolly matrixed in some way. The easiest way to go is run 2 wires from each contact area on the pad's pcb to the related switch. That way you don't end up with a screwed up wiring scheme.

http://imageshack.us/photo/my-images/181/dsc00032ux3.jpg/

See how there's 2 traces to each contact? Scrape the solder mask off on a spot of each trace and solder your wires there.

[Guywiththegun]

Ok, I'm gonna go with that strategy since its much simpler than finding a common ground. But what do you mean by the 2 traces and the contacts? By contacts I assume you mean the big squares marked "SW5" (correct me if I'm wrong) but what are the traces?

[bkenobi]

Scrape the solder mask off on a spot of each trace and solder your wires there.

Isn't it better to trace the trace back to a solder point?  I have never tried soldering to a trace itself, but I would assume they would tend to lift pretty quickly with slightly too much heat.  They also don't have any means of strain relief.  If you can solder to a pin or pad, then you are attaching to a designed connection point that will stand a chance of lasting some time.

[HaRuMaN]

Solder points may be hard to find.  If you prep the pad properly, it will work just fine. 

Even though my tutorial is for a xbox 360 pad, you can still follow the steps:

http://forum.arcadecontrols.com/index.php?topic=64050.0

[Guywiththegun]

Great tutorial. Those spots for the button connections look much easier to understand though. My gamepad contacts (if thats what they're called) look much more like the ones boardjunkie posted:

http://imageshack.us/photo/my-images/181/dsc00032ux3.jpg/

Where would I put each wire on those contacts? Looks like a maze or something. And does it matter which wire goes to which spot?

[HaRuMaN]

Each of the the squares where the button was has 2 traces in.  You could do it there, or you could follow each line to a solder point.  As long as you have the two for each button, it'll work.  Doesn't matter which wire goes where, you're just completing a circuit.

[Guywiththegun]

Awesome, thanks! I hooked up a button and held the wires to the spots you outlined with some tape, just to test it . . sure enough, the button worked. Does that pretty much mean I'm on the right track now? I mean, if I didn't have both wires touching the right spots, the button wouldn't work, right?

[HaRuMaN]

Correct