MPR121

Sensors

3

Freescale Semiconductor

Touch Sensing

Once the capacitance is determined at any given moment, this information must then be translated into intelligent touch

recognition. The MPR121 has a couple of systems that have improved over the previous generation in the MPR03x series

devices. A baseline tracking system allows the system to track the untouched capacitance in the system. For information on how

to set up the baseline capacitance system refer to application note AN3891. The baseline value is then compared with the current

value to determine if a touch has occurred. A designer has the ability to set both the rising and falling thresholds in addition to a

debounce to eliminate jitter and false touches due to noise. These elements are described in application note AN3892.

Proximity Sensing

A new feature of the MPR121 is the use of a proximity sensing system whereby all of a system’s electrodes can be shorted

together internally and create a single large electrode. The capacitance of this electrode is larger and projected capacitance can

independent set of configuration registers. This system is described in application note AN3893.

LED Driver

The MPR121 includes eight shared LED driving pins. When these pins are not configured as electrodes, they may be used to

drive LEDs. The system allows for both pull up and pull down LED configurations as well as general GPIO push/pull functionality.

The configuration of the LED driver system is described in application note AN3894.

Serial Communication

described in AN3895. For reference the register map of the MPR121 is included in Table 1.