Persistence of Vision Robot, aka Mr. Spinny

[Lorenzo M. Oliver]

OK, here we go -- the concept is quite simple -- a small tabletop 'bot
with a single QRD1114 IR/emitter sensor on the bottom runs around
looking for a black tape line (same line that a line-follower might pick
up). Upon finding the line, the 'bot spins *very* fast and uses the
seven-LED bank to do persistence-of-vision text. As the sensor passes
the line on each revolution (actually, twice each revolution), it uses
the line as a "sync mark" to restart the first column of pixels of the
text string.

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. The same detector
is used for a "cliff" detector as well (RC decay on the QRD1114). A cds
cell with sigma-delta ADC is used for determining if it's too bright to
make POV worthwhile.

http://forums.parallax.com/forums/default.aspx?f=21&m=358502