Opto-Interrupter: Coin Sensor and Race Track Finish Line
There are 3 H21A2 opto-interrupters in our project. The first detects a coin a it enters the machine. The other two detect when a car crosses the positions associated with the start and finish lines. In order to activate the latter two, the lines that are fixed to the cars have tabs which slide through the gap of the H21A1. All opto-interrupters use 10kΩ pull down resistors at the H21A2 photransistor’s emitter. This ensures that the output of the opto-interrupter is tied down to ground when something blocks the IR LED’s light and is 5V otherwise.