Slave flash trigger
The circuit in the diagram is intended for synchronous, wireless triggering of one or more slave flash units when the mother flash is triggered, so as to obtain better lighting of the photographic object.
Phototransistor T1 is switched on upon the receipt of the light of the mother flash unit. The potential at the inverting input of comparator IC1a rises, the comparator toggles and for a brief instant, determined by the value of C1, the voltage level at the inverting input of IC1b is lower than that at the non-inverting input. This causes 1Cib to toggle momentarily, which results in the thyristor being triggered and the flash contacts to be closed.
The circuit may be used in dark as well as brightly lit places. The operating range depends on the mother flash and will formally be 5-15 m (15-50 ft). The sensitivity depends primarily on the base resistance of the phototransistor and this rna• be modified according to circumstances. Any tendency to instability may be cured by shunting R2 with a 100 pF capacitor.
Power is supplied by a 9-V (PP3) battery.