Given how much time I've spent troubleshooting, I'm a little disheartened it didn't get me anywhere. I still haven't been able to communicate with the joystick from an Arduino.
Today I, once again, took a screwdriver to the Zinger and tore it down. This time around, I took a closer look at the circuit board and snapped a couple of photos.
Next, I grabbed my multimeter and made sure everything was hooked up the way I expected it to be. No shorts circuits or other nasty surprises. I took note of the single integrated circuit on the board and which of its pins each wire ended up at.
Markings on the IC yielded no result when searching the interwebz. Lacking a proper datasheet, I can never be 100 % sure I've made the right assumptions concerning the pinout. Maybe I got it wrong somehow, and that's why I can't get data off the joystick.
Anyhow, with the PCB exposed I connected the pins directly to my logic analyzer and Arduino Uno and started running my test program – I'll get into more details in a future log entry – and, just as before, the clock (CLK) and latch (OUT) signals from the Arduino to the joystick looked okay, but the data signal (D0) from the joystick was flat. No matter what.
That's it, I'm stuck. At least with this particular joystick. Maybe it tanked during my investigations or perhaps it was already broken when I bought it. (I never confirmed with an actual NES that the joystick actually worked.)
To move forward, I need another Zinger to experiment with. Or some other interim controller, utilizing the NES protocol, like an original NES or SNES controller. I lack the former, but the latter is actually in my possession. Somewhere.
Maybe I'm not stuck, after all.