What is a nickelphone?
It's a coin-based music keyboard. 15 nickels and 10 pennies act as touch sensors on a traditional 25-key piano-style layout. It can emit simple square wave tones through an onboard piezo buzzer, but its primary use is as a MIDI keyboard, so it can drive a full synthesizer (like FL Studio on PC). It 's based on an ATmega644 microcontroller, chosen because each key needs its own pin, and this chip has 32 data pins (8 of them analog inputs). It uses the "no extra parts" capacitive sensing method developed by Mario Becker and others.