MPR-121 Proximity Capacitive Touch Sensor Controller

The MPR121 is the Capacitive Touch Sensor used in the Doboz TSNM 3U/4U and XIIO DIY projects. 
It is the second generation capacitive touch sensor controller after the initial release of the MPR03x series devices. The MPR121 features increased internal intelligence, some of the major additions include an increased electrode count, a hardware configurable I2C address, an expanded filtering system with debounce, and completely independent electrodes with auto-configuration built in. The device also features a 13th simulated sensing channel dedicated for near proximity detection using the multiplexed sensing inputs.