Parts List-
R1, R2 - 2 - 100 Ohm 1/4W Resistor
R3, R4 - 2 - 100K 1/4W Resistor
D1, D2 - 2 - Standard LED
SCR1, SCR2 - 2 - 6A, 200V SCR (such as the 106B)
S1, S2 - 2 - See Notes
K1 - 1 - Small 12V Relay
MISC - 1 - Board, Wire
Notes
1. S1 and S2 are small lever type micro switches. Most any kind will do, as long as they are sensitive enough to be activated by the wheels of the cars. They should be positioned on the track so that the front wheels of the cars will run over them as the cars just cross the finish line.
2. To reset the circuit, disconnect and then reconnect power. You can add a normally closed switch in series with the power supply to make this easier.
3. There is no reason this circuit cannot be used to tell the winner of a foot race, bike race, slot car race, etc.
