Home Electronics Top Coin Sensor
	Electronics - Top Coin Sensor A H21A2 slot detector was used to detect when a coin was inserted into the Plinko MPAG. The output from the detector was then input into an inverting comparator (LM339) with a reference voltage of 2.5V and a hysteresis band of 0.05V to generate a quickly changing digital output. When no coin is present between the emitter and detector, the output of the circuit is low. As soon as the pathway is blocked by a coin, the circuit outputs a high signal. The forward voltage of the emitter is rated 1.7V at 60mA, by choosing a 120 Ω resistor, we assured that a current of 27.5mA through the LED which is more than sufficient to saturate the detector. When no coin is present, the detector generates a current of roughly 1.4mA. In this state the output to the comparator is 4.6V, well above the 2.505V needed to switch the comparator's output from high to low. When a coin blocks the IR emitter, the only current from the detector is leakage current. In the worst case scenario,  the leakage current is 100nA, and the output to the comparator is 0.3mV, safely below the 2.495V necessary to swithch the compartor output from low to high.. The LM339 comparator has a turn on time of 8μs, and a turn off time of 50μs.These switch times are more than fast enough to detect a coin passing through the slot detector.