Slave Flash Trigger


The flash that is built
into digital cameras is designed for indoor photography. At subject
distances of greater than five meters or so, the light is usually not
powerful enough to take a satisfactory picture. Unfortunately most such
cameras do not include a shoe for an external flashgun, and so a
light-triggered slave flash is called for. The flash built into the
camera produces a very rapid change in light intensity which is picked
up by a photo-transistor in the slave.

The pulse is transmitted via C1 to the transistor, which then
briefly shorts the contacts on the slave gun together. The sensitivity
of the device can be adjusted using P1. The circuit can be connected to
the shoe contacts of the slave flashgun using a coaxial cable, or, with
space permitting and a nimble bit of DIY, can
be built inside it. The circuit is not suitable for use with flashguns
which have a voltage of more than 20 V across the trigger contacts, or
with cameras that emit a number of ‘preflashes’ before taking the
picture proper.

Slave Flash Trigger Circuit

Slave Flash Trigger Circuit Diagram

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