Build a simple light following robot with common low cost parts. You will need a soldering iron, hot glue gun, and an ohmmeter if you do not have matched light sensor cells. This robot will follow light from a flashlight. These parts are available at many electronics suppliers, and are common in on-line surplus outlets.



Parts and Tools:



1) Two small DC motors, with fairly long shafts.

2) Three popsicle sticks

4) Two potentiometers, around 10K

5) Two (matched) CdS cells

6) Insulated wire

7) Two N-Channel MOSFETs

8) Two diodes, preferably fast switching type

9) Tube or shrink-tubing to use for wheels

10) [optional] 1/2 ping pong ball, or metal thumb-tack, to use for rear skid.

11) Hot glue, and hot glue gun

12) Solder, soldering iron

13) Multimeter (only needed if you need to select CdS cells)

14) 9v battery plug

15) 9v battery



On-line surplus electronics stores often sell large bags of Cadmium Sulfide (CdS) light sensor cells, which are Light Dependant Resistors (LDRs) for reasonable prices. When using cells from such a grab-bag, you should be careful to select two matched cells with a similar resistance under both low and bright light. The values of these cells can vary significantly. Matching to within 10-20% is sufficient.



This robot is based off of two mirror-image motor driver circuits as shown here. The photocell on the left side drives the motor on the right, and vica-versa.