Flash Detector

Our flash detector circuit takes in the current sum of three phototransistors. The three sensors are wired in parallel and feed into a current sense resistor (24K) with an op amp (LM324) in current sense configuration. The noninverting input of the 324 was then adjusted with a potentiometer to have an input voltage high enough to reject noise, but still be able to trigger on a flash (4.28 V). The output was fed into a 74HC14 hex inverter with schmitt trigger to eliminate noise, giving a minimum hysteresis of 0.7 V.