The total amount of light that falls on the photodiode is what sets the timing of this accumulative light circuit. Parts of the circuit. 555 timer integrated circuit: Wired as a (digital) inverter Schmitt trigger. Low input (below 1/3 supply voltage) to pin 2 sets the output High. High input (above 2/3 supply voltage) to … Continue reading "Accumulative light trigger switch circuit – 555 timer and photodiode – Electronics lesson"