This kit includes a round printed circuit board (PCB) with holes spaced on a 0.100" grid, one extended 2×7 male header, two extended 1×2 male headers, one 2×7 female header, two 1×2 female headers, four 7/8" nylon spacers, four 1-1/4" screws, and four nuts.

The expansion PCB matches diameter of the 3pi chassis and mounts just above the tops of the wheels using the four included screws and spacers. Once assembled, the PCB has electrical connections to the base that allow you interface your own electronics with the 3pi robot, which is sold separately. These connections give you access to the ATmega168’s free/jumpered pins, as well as to the three on-board voltages: VBAT (battery voltage), VCC (regulated 5 V), and VBST (regulated 9.25 V that is supplied to the motors). Additionally, the expansion PCB connects to the base’s power button and battery charge port, allowing you to add your own power buttons and charge ports.

This expansion kit’s PCB has cutouts that allow you to view the LCD below and access the power button, reset button, and ISP programming header. If you want additional I/O lines or extra prototyping space and you do not need the LCD, please consider the version of the expansion kit without cutouts, which replaces the LCD. For a more advanced expansion kit, please consider the m3pi expansion kit, which lets you turn your 3pi robot into an m3pi robot.