PS2 gamepad hack question

[elvis]

I managed to pick up some Playstation 2 controller PCBs for next to nothing for a joystick-building project I am working on.  These are just bare PCBs with nothing on them but the main "cpu" (logic unit, or whatever it is).  No motors, no analogue sticks, no casing.  Just the raw PCB, logic, and cable to connect it to a console.

Interestingly enough, a PS2 will not boot into games with one of these plugged in.  I can boot a PS2 with a normal gamepad plugged in, and then insert one of these pads and it will work fine.  The buttons all appear in analogue mode without any dramas, and a circuit from the button input to VCC works in analogue mode.

I'm guessing that when a PS2 fires up it searches for working gamepads, and part of that search is the analogue componentry.  Seeing as I don't have the analogue thumbsticks *CONNECTED* to the PCB, it deems the pad non-functional.

Does anyone know anything about how these pads work?  I've bought some trimpots (potentiometers) from a local electronics shop that seem to match the resistance values of a genuine Sony PS2 Dual Shock that I have lying around.  I'm going to solder those on and try again.  But if anyone can point me in the right direction of what I need to do to get these PCBs reckognised on boot, I'd be greatful. 

[elvis]

More investigation shows that the analogue thumbsticks do indeed have a default resistence when in the idle positions, which is why the pads don't function without them connected.  I bought some trimpots and am testing various combinations, but it's all flying blind so far.

[elvis]

I found an old MadCatz pad I had lying around and pulled the thumbsticks out of the circuit to measure them.  100K trimpots on them.  That might solve my dramas.

[elvis]

Nope, no joy.  The outputs from the analogue controls are still all over the shop.

*sigh*.  So much for my big plan to save some bucks when mass-producing sticks.  Back to hacking expensive Dualshocks, I guess.

[MrQuan]

If you have some dual-shocks, or third-parties there, couldn't you just hook up a multimeter and measure the resistance across the analogue sticks when in their 'home' position?  Then it would just be a matter of matching that by soldering resistors to the PCB.

[elvis]

If you have some dual-shocks, or third-parties there, couldn't you just hook up a multimeter and measure the resistance across the analogue sticks when in their 'home' position?  Then it would just be a matter of matching that by soldering resistors to the PCB.

Third parties.  And I did exactly that - measured existing analogue sticks out-of-circuit, and replaced them with identical vertical potentiometers in the "home" position.  That still didn't work however.

[MrQuan]

100k doesn't sound right though???  - I dunno... they are third-party though.  I dismantled one of my dualshock2 controllers and measured the resistance.  It came out at 4kohms (give or take a few decimals).

I've marked up a photo below to show you how it should be wired, in theory.    Of course this is a Sony one, I'm not sure if thrid-parties are vastly different.  Anyways, resistors are only a few cents each so it's still worth a try I guess.

[elvis]

I've marked up a photo below to show you how it should be wired, in theory. 

Did you measure in circuit, or out of circuit?

Measuring in circuit yields incorrect measurements courtesy of the analogue trickery going on in these pads.

Measuring a third party pad I pulled apart in-circuit gave me readings of 2K.  Measuring out of circuit gave me 100K.  The reason is simple: remember the math behind calculating the residence in parallel versus in series.

I'll definitely give your markup a go with some resistors, but I have a funny feeling they will give me the same results.