Capacitive Touch Wheel Testing (with MPR121 IC)

I wanted to start experimenting with capacitive touch scroll wheels to incorporate into my automation system as the input for a dimmer or some such.  I looked around to see what was out there and saw this thing.  I decided to make one similar to it for some testing.

There's a lot of info about Cap Touch in the arduino world.  At first I was going to just do the cap touch directly with an arduino which proved to be problematic due to i/o limitations.  Another option was to use a multiplexer.  I made another board (linked here) to test multiplexing that only had 8 segments (I only had some 8 channel multiplexer chips laying around).  This proved to be too slow getting and dealing with the data. 

I ended up using a MPR121 which is an I2C capactive touch sensor chip.  The breakouts for these are cheap so it was a good choice.

I hooked up the board I made to an arduino and the MPR121 just with some wire and a breadboard.  When testing I used the MPR121 library from Adafruit and modified one of their example sketches.  The results were very robust for detecting which pad was pressed and unpressed and therefore simple to detect if a person is moving their finger clockwise or counter clockwise.

Heres some pics of making the board:

Front of board after etching and applying solder mask:

Back of board after etching and applying solder mask:

Front of board after assembly:

Back of board after assembly:

Here's a sample image of the MPR121 I2C breakout that can be gotten cheaply from the internet.