CPX A0 is not reliable for touchio.TouchIn

[dhalbert]

CPX A0 is connected to the speaker, so it will not work for touch input if the speaker is in use. This should be documented if it's not already

In addition, Touchio.TouchIn(board.A0) often ends up with a very high initial threshold value when the object is created. If you deinit() the object and re-create, the threshold is more reasonable and is closer to the raw_value read later. I tried reading the value twice on during construction but it was still high to being with.

[caternuson]

The new guide does a good job of documenting this:
https://learn.adafruit.com/adafruit-circuit-playground-express/pinouts

[dhalbert]

Should we just remove A0 from the allowed pins for TouchIn?

[kattni]

That would be my suggestion. I specifically didn't include it in the CPX touch API because of the inconsistency.

[dhalbert]

Fixed by #330. A0 is now not allowed for TouchIn, only on CPX.