is it possible to have pc cable (camera) trigger a disposable camera's flash circuit

Thread view:

Enable EMail Alerts

Start New Thread

Thread rating:

krem - 13 Jul 2005 17:38 GMT

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.

Reply to this Message

Bandicoot - 16 Jul 2005 16:16 GMT

> Hello, A strange request maybe but an answer would be
> great. I"m looking to use the flash circuit inside of the
[quoted text clipped - 7 lines]
> 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

Reply to this Message

dj_nme - 17 Jul 2005 02:11 GMT

<snip>

> 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
[quoted text clipped - 11 lines]
>
> Peter

If you feel like making a small protection circuit, I have and idea.
Use a relay to close the contacts in the disposable's flashgun trigger
and the pc synch from the comera to complete the circuit for the low
voltage (3V or 6V, depending on the relay) that actuates the relay.
A "stubber" diode across the solenoid on the relay should protect your
camera from the induced voltage from the relay when the power is cut (by
your camera) when the shutter has closed.

Reply to this Message

RSD99 - 17 Jul 2005 05:15 GMT

> If you feel like making a small protection circuit, I have and idea.
> Use a relay to close the contacts in the disposable's flashgun trigger
[quoted text clipped - 3 lines]
> camera from the induced voltage from the relay when the power is cut (by
> your camera) when the shutter has closed.

Problem:
(1) Relays take time to close.

FWIW: Plan on something like 50 mS between applying power and contact
closure. That's roughly 1/20th second.

Problem:
(2) Relays consume a considerable amount of power.

FWIW: Plan on something like 20 mA at 5-6 volts.

Therefore:
Not really practical. Look around for a circuit using something like an
SCR.

Reply to this Message

dj_nme - 17 Jul 2005 07:07 GMT

>>If you feel like making a small protection circuit, I have and idea.
>>Use a relay to close the contacts in the disposable's flashgun trigger
[quoted text clipped - 18 lines]
> Not really practical. Look around for a circuit using something like an
> SCR.

I was realy just doing that off the top of my head, never tried it myself.
An SCR circuit would be a better option.

Reply to this Message