This is a small microcontroller board using an attiny85 (programmed using damellis' attiny core for Arduino via MIT's High Low Tech group) to read the resistance from a sensor (in this case, galvanized nails to measure when a houseplant needs to be watered) and report via xbee. Uses watchdog timer to sleep (and sleeps the xbee via pin sleep), sends one sample every few hours. Boards were made via SparkFun's Batch PCB, so not uploaded to OSHPark yet.

photos (Photo credit Paul Horowitz.)