Pete’s lawn sprinkler was covering too much unnecessary ground (pavement) so he designed a method for regulating the water supply based on the sprinkler’s position –

I’m using a similar setup to the rudder control on my model airplane. The cable gets pulled in and out as the sprinkler turns (kind of like a rudder). The cable then turns another servo horn attached to the potentiometer inside that black box. From my arduino board, I send the pot VCC/GND and a third conductor to sense the position of the pot. (three conductors total = why not use extra mic cable I had lying around my garage). After a little averaging on my ADC I was able to get a pretty smooth reading of the position. The servo horn and cable apparatus is a pain to setup, so I’m excited to just hot-glue a compass or gyro to the top of my sprinkler for the next setup!

[via Sparkfun]