The Solar Engine Circuit can be combined with light-detecting
devices so that a Robot can move towards or away from a light-source. This adds
realism to its "artificial intelligence."
The circuit for this robot consists of two Solar Engines with 1381J voltage detector IC's (digikey part #MN1381-J-ND) and two photo diodes(digikey part #LT1032-ND). These photodiodes cause the Solar Engine on the opposite side to fire and the Solar Photovore turns toward the light source. The motors are two pager "vibe" motors with the weights removed, from Solarbotics type Namiki 1701. The 100k potentiometer on the "head" balances the two Solar Engines.
If you want a full kit with all required parts and a very high quality PCB, go to Solarbotics.
Here is the layout as shown on Lee's RoboGallery site:
If you are unable to get the 1381 Voltage-reference IC's, here a circuit that uses LEDs to detect the trigger voltage:
Photovore by PiTronics
The Photovore Robot shown above uses two clock mechanisms to
drive the wheels. The clock-motor is normally driven from a 1v5 cell and pulsed
every second when used as a clock. But the "motor" speed can be
increased in RPM to provide rotation for a robot. A 30:1 reduction drives the "seconds" hand and this
is used to drive either the left-hand or right-hand wheel (two mechanisms are
needed). The clock mechanism is taken apart and the chip,
plus some of the gears are removed.