My second effort in BEAM Robotics has been the creation of a Phototrope Photophile. Phototropes are small BEAM-bots that respond to light and are mobile. This phototrope is attracted to light, so it is a photophile (verses a photophobe which fears light).
This photophile uses a two photopopper circuits. Photopoppers are a store and release circuit that uses a capacitor to collect electricity gathered by the solar panel(s). A flashing LED (FLED) is used to determine the threshold at which the capacitor is discharged into the motor(s). FLEDs have a unique attribute in that they function less efficiently when exposed to light, allowing the photophile to respond directionally to light.
Here's a video of the little guy working his way across the tile entry in our house. This video is taking in late December - so the sun's angle is at it's lowest. I've bent his bottom down a bit to give him a better angle of attack towards the sun - it helps a bit but his is a somewhat slow mover (as you will see).
