It consists of two QRD1114 sensors, one for each wheel, fed into an LM339 with two 5K trim pots to allow for adjusting the sensitivity. The outputs from the LM339 go two two digital pins on the Arduino.
The parts list looks like this:
- 2 - FAIRCHILD SEMICONDUCTOR QRD1114
- 1 - FAIRCHILD SEMICONDUCTOR LM339AN
- 2 - TRIMMER, POT 5KOHM 23TURN THD T93XB-5K-10-D06
- 2 – 220 Ohm Resistors
- 2 – 10K Ohm Resistors