OSH Park engineer Jenner Hanni posted on Wickerbox Electronics about his Arduino Theremin project:

This is a sort of false theremin that turns the distance between your hand and the rangefinder into notes. There are three cap sense pads you can touch to change the key, and the program remembers your most recent song so you can choose to play it back.

The KiCad schematic and layout, along with the the Arduino code, have been released on Github under the CERN Open Hardware v1.2 License:

wickerbox/Arduino-Theremin

Jenner shared the board on OSH Park:

Arduino Theremin v1.3