It seems I can't post to or edit the new wiki post, so I will just post it here: I am not yet sure which type of input circuit I like best, but this one is possibly a bit better than the previous posted. This one only uses the supply voltage from Axoloti, so it is more general.
- Again, the signal is inverted. So -5V to +5V maps to +3.3V to 0V.
- If no input is connected, it doesn't go exactly to the mid point, so the readout will not be "0". I couldn't find an elegant way to fix that, but if you use a minijack connector you can use the "normal" connection wired to ground (as shown), which is a reasonable solution.
- I haven't tested this exact circuit yet.