Adafruit MPR121 Library 
Tested and works great with the Adafruit MPR121
- https://www.adafruit.com/products/1982
- https://www.adafruit.com/product/2024
- https://www.adafruit.com/product/2340
Check out the links above for our tutorials and wiring diagrams. These sensors use I2C to communicate, 2+ pins are required to interface
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Written by Limor Fried/Ladyada (Adafruit Industries). MIT license, all text above must be included in any redistribution