This is the second version of B.bro. I changed from the boost regulator to a linear regulator for the power supply, and changed the dual H-bridge to a chip that's about a third the cost of the first version. You can also see I've switched from perf-board construction to etching my own boards. This guy is the same diameter, about 75 mm, but he's taller, about 85 mm. You can see around the edge of main board are a series of three pin headers. These connectors take modular sensor daughter cards. The two in the picture are IR proximity sensors, but I've also built passive IR sensors and visible light sensors. So far the software only works with the proximity sensors.