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I have received countless emails asking for a circuit to tell the user which car won in a pine car (also called Pinewood Derby, Cub Car, Scout Car, etc.) race. This simple circuit takes care of the guesswork, lighting the appropriate LED to indicate the winner.
| 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 |
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.