Instructables
CustomKeys is a customizable, Arduino-based, polyphonic synthesizer. The CustomKeys keyboard uses capacitive touch sensing - each key is made of a conductive material which, when touched, signals the synthesizer to emit a tone from the speaker. The CustomKeys library allows the user to choose an 8-note musical scale for the keys. Furthermore, users have a creative choice on the body design of their CustomKeys synth - users can use a provided laser cutter template or use any other material long as the basic requirements for the system to function are met. 

Special thanks to:
- Joe Marshall, whose code for the Arduino Octosynth (http://www.cs.nott.ac.uk/~jqm/?p=605) is the basis of the CustomKeys library
- Instructables user blinkyblinky for documenting how to assemble the Arduino Octosynth http://www.instructables.com/id/The-Arduino-OctoSynth/

 
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Step 1: Materials

Picture of Materials
You Will Need:
- The CustomKeys Arduino library - updated 05/15/13 (download below)
- 8 bits of conductive material for the keys (paperclips, brads, conductive tape, etc.)
- Colorful card stock paper (unless you're going the laser cutter route)
- A soldering iron
- A boxcutter or x-acto knife
- Stick glue
- Wire clippers and strippers
- A set of 8 male header pins 
- Electrical wire
- An Arduino ( I used the Uno)
- A USB for the Arduino
- A breadboard
- An 8 Ohm speaker

If you have access to a laser cutter:
- 16" x 20" birch board with 1/8" thickness
- The box template (download below)*

Optional:
- Jumper cables (preferable to wires, but wires work just fine)

You may find that the output sound is too quiet with the speaker alone.
In this case, you may want to build an amplifier circuit. Here are the parts you will need: 
- An n-type MOSFET (I used an IRF9530)
- Two 100 Ohm resistors
- A 1.2K Ohm resistor
- A .47uF film capacitor
- A 220 uF electrolytic capacitor

*Part of the box template was made with Rahul Bhargava's BoxMaker http://boxmaker.rahulbotics.com/