a tabletop "persistence of vision" robot
The concept is quite simple -- a small tabletop 'bot with a single sensor on the bottom runs around looking for a black tape line.
Upon finding the line, the 'bot spins *very* fast and uses the seven-LED bank to do persistence-of-vision text.
Basically it sits around showing a dim pattern on the LEDs and plaintively beeping occasionally. When disturbed, it roams around and does it's POV thing when it finds a line.
A small calibration routine is run upon powerup/reset that lets the user hold the 'bot over the tabletop surface, the line, and the "cliff" edge so... the stored values are used for determining thresholds for surface, line and cliff edge detection.
In any case, the basic chassis is a CD spindle case. A thin bit of craft plywood was glued on the underside to stiffen it up. Minimal parts were used (see plans and cutting template PDF) on the construction page).