You just need attiny 85, CD4051 (any analog multiplexer) and buzzer to make a touch piano....
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Step 1: Connections
Circuit is as easy as it gets, So you can easily recreate circuit using image i posted. Note that the buzzer's left side is ground and other connects to 3 to 5 volts +ve.
Step 2: Upload the Code
I posted the code and Commented the part you can make changes so download it and upload
it to attiny 85. I used arduino uno to programme the attiny85 chip if you don't know how to upload
code to attiny 85 you can easily find an instructables for it.
Step 3: Connect Touch Wires
NOW all the remaining unconnected Pins on analog multiplexer will sense touch and will return value from 0 to 17. 0 when nothing is touched and it will increase when touched. You will find a variable called touchThreshold in code you can change its value to change the sensitivity of touch. All the purple colour wires you see in image are all touch sensitive. The very small aluminium wires are only for supporting the purple wire and has nothing to do with the circuit. If you do same use unused line in breadboard to do so.
Step 4: The Backside
I took out the paper from the backside of mini breadboard to expose the sticky part. And i Stripped the ends
of purple wire and sticked them to breadboard and then i cut the square blocks of aluminium foil and sticked it on the top of stripped wires. Thats it guys thanks for reading this instructables.
See it in action.