This kit includes a round printed circuit board (PCB) with holes spaced on a 0.100" grid, two extended 2x7 male headers (MCM Part# 28-17708), two extended 1x2 male headers (MCM Part# 28-17709), one 2x7 female header(MCM Part# 28-17729), two 1x2 female headers (MCM Part# 28-17715), four 7/8" nylon spacers, four 1-1/4" screws, and four nuts.
The expansion PCB matches the 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 (MCM Part# 28-17626, which is sold separately. These connections give you access to the ATmega's LCD pins, ISP programming pins, and 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.
Note: This expansion kit replaces the 3pi's LCD. If you want to preserve the LCD, please consider the version of the expansion kit with cutouts or the more advanced m3pi expansion kit.
This version of the kit might be preferable over the version with cutouts to those who want additional I/O lines or extra prototyping space and do not need the LCD. A wireless module, for instance, might need the I/O and make the on-board LCD unnecessary if data is relayed to a nearby PC. For a more advanced expansion kit, please consider the m3pi expansion kit (MCM Part# 28-17628), which lets you turn your 3pi robot into an m3pi robot (MCM Part# 28-17627).
The expansion PCB is designed to provide plenty of prototyping space for your components. It has room for two 0.6" 40-pin DIP (dual in-line package) components, such as the ATmega32 in the picture below, or for numerous smaller DIP components. The prototyping space extends all the way to the edge of the PCB, allowing you convenient points to mount a variety of sensors such as bumper switches and range-finders. The silkscreen shows how the pads are connected; the electrical connections are on the bottom side. You can cut the copper traces on that bottom side (with a sharp knife or a small rotary tool cutoff wheel) if some of the pre-made connections interfere with your desired layout.
Two of the unused I/O lines on the 3pi's microcontroller are its serial transmit and receive lines. This means that you can add a second microcontroller or microcontroller board, such as a Baby Orangutan, Basic Stamp, or Arduino Nano, to the expansion PCB. This second microcontroller would deal with all of the sensors and additional hardware on the expansion PCB and control the base via serial commands. We have released a serial slave program for the 3pi base that turns it into a serially controlled platform that can be driven at the whim of another microcontroller.