I'm trying to figure out how to interface a microcontroller with a cheap MP3 player that used snap domes for buttons. I do not have a datasheet for anything on the MP3 player board, because I can't find any reference to the main IC's model number on Google. The front of the board looks like this:
I scoped the inner and outer snap dome pads to see how they were configured, and got some strange results.
The Top, Middle, and Right pads behaved how I expected: The outer rings scoped as ground and the inner circle scoped at 3.3 volts.
However the Left and Bottom pads were strange: Both the inner and outer pads were at 3.3 volts. Notice these buttons have pads look different from the other 3. Also The MP3 Player worked fine before I took it apart, and I was gentle in dismantling it so I don't think I damaged it.
I'm wondering what to make of the signals from these two pads. It doesn't seem like pressing the two buttons (and closing the circuit between the two pads) would do anything because they are at the same potential. Is there something I'm missing? Thank you.