Flash Slave Trigger

Flash slaves are used when you need to supplement one flash unit with one or several more. This slave trigger simply triggers those other units. It does this by "seeing" the first flash (using a phototransistor) and triggering the other flashes a few microseconds later. The sensitivity of the circuit is adjustable to compensate for ambient light or dimmer than usual master flashes.

Schematic

Parts

Part Total Qty. Description Substitutions R1 1 47K Linear Pot R2, R3 2 3K 1/4W Resistor R4 1 220 Ohm 1/4W Resistor R5 1 680 Ohm 1/4W Resistor C1 1 10uf 25V Electrolytic Capacitor C2 1 0.047uf 25V Ceramic Capacitor Q1 1 2N5777 NPN Darlington Phototransistor Q2, Q3 2 2N3904 NPN Transistor 2N2222 SCR1 1 400V 2A SCR S1 1 1A 120V SPST Switch P1 1 Plug to match jack on slave flash MISC 1 Knob For R1, Wire, Board Notes Q1 should be aimed at the master flash. R1 should be adjusted for maximum sensitivity but no false triggering. Keep your fingers away from SCR1 when the circuit is operating. It is at 50V-300V and will give you a nasty shock