Pine Racecar Victory Judge

Schematic

Parts

Part Total Qty. Description Substitutions 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.