Flash-Triggered Pulse Stretcher Using Classic Monostable Circuit

This is a flash triggered (photo-driven) circuit which produce a pulse with constant predetermined wide. This circuit can be used to control any device which is required to be synchronized with optical trigger/flash light.  The pulse can be used to drive relay (after proper power buffering,  to drive other circuit logic, or electronic switch.  We call it a pulse stretcher because the short flash light will be converted into longer fixed width.  The flash light duration can have inconsistent width but the circuit will produce a consistent one, which is determined by the 10uF capacitor and the 4.7k resistor (you can replace the capacitor to get different pulse width setting). Here is the schematic diagram of the circuit: