krem said:
Hello, A strange request maybe but an answer would be
great. I"m looking to use the flash circuit inside of the
disposable cameras (with flash) with an older camera I
have. The camera uses whats called a "pc cable" as a
trigger and i'm looking for some type of circuit which can
close the disposable camera's flash circut from the signal
coming from the pc cable. I'm not sure what the signal is
though so that may be my biggest stumbling point. Thanks
for any input. Ahh and i'm using a disposable camera flash
because i'm trying to shoe horn it into another old flash
housing to keep the old look of the camera.
The PC connection is just a 'switch': it is open until you press the
camera's shutter release, and then the switch closes just before the shutter
opens (it opens again soon after, normally when the second curtain of the
shutter starts to close.) So the 'signal' is simply completion of the
circuit. Make sure your PC connection is X sync: if it is B of F the
circuit will close too soon and your flash will fire before the shutter is
fully open. (That's because flash bulbs, for which the B and F type sync.s
are meant, take longer to reach maximum brightness than electronic flash
tubes, so they have to be triggered sooner.) Then all you need to do is
find the wires inside the disposable that represent the 'trigger' circuit
and insert the cable from your PC socket as the 'switch' in place of the one
from the disposable's shutter release.
Two things to be aware of:
1. Electronic flash operates with very high voltages, and so you will have
to be very careful when you take apart the disposable camera. Make
absolutely sure you can disconnect its battery before you touch any other
parts, and then be sure the capacitor for the flash is discharged before
proceeding. ie., proceed with caution and at your own risk!
2: Normally a flash gun uses a (relatively) low voltage trigger circuit to
fire the much higher voltage to the flash tube. (Some older electronic
flashes do have high voltage trigger circuits as well.) High trigger
voltages can fry modern electronic cameras, and if high enough can damage
older cameras too by welding their flash contacts shut. I've no idea what
the trigger voltage in a disposable is - maybe it's cheaper to use a low
voltage so the trigger switch can be made less robust, or maybe it's cheaper
to leave the voltage high and use a tougher switch but save on having a
separate low voltage trigger circuit. I'm sure cost will be the deciding
factor. So be careful in case you get a very high trigger voltage hitting
your camera.
HTH
Peter
