The Proximity Plug is a small board which uses the MPR084 to support up to 8 capacitive input (“touch”) switches. A solder jumper allows using up to two of these plugs on a single port. The chip can be configured to allow only single touch or multiple switch contacts at the same time, and will do an auto-calibration to adjust for differences between the sensor surfaces.
An I2C bus running at 3.3V is used as interconnect, with all the power and signal lines brought out to to both sides of the board to allow daisy-chaining with other I2C-conformant boards.
The Assembled Proximity Plug comes with the SMD-sized MPR084 chip and resistor array, as well as the decoupling capacitor already soldered onto the board. Headers for this and all other JeeLabs plugs can be found here (straight) and here (right angle).
The PCB Only version contains just the printed circuit board for the Proximity Plug. No parts, no headers.
The documentation and full design details are freely available.