MPR121 Proximity Capacitive Touch Sensor Controller
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The MPR121 is a I²C device which can be used to implement touch keys. It can also function as a GPIO extender and can be used to drive LEDs.
In order to try out the MPR121 I created a quick keypad.
Rev. a was a bit of a rush job and I managed to get one thing fundamentally wrong. For some bizarre reason, the MPR121 can supply 17 mA on the LED pins but it can only sink about 1.5 mA, so LED's should not be active low on these pins but active high. Also, by rearranging the rows and columns, the actual routing got quite a lot neater.