Centretek said:As a keen amateur photographer, I used to have a studio setup using slave flash triggers. However some dirty mongrel burgled my house and stole all my camera gear.
I've replaced most of it but the flash triggers are now about $70 each so I want to build a few.
Searching the net, all I can find are silly PIC contolled units and others that require batteries.
The originals, used on cheap small flash units, used the 200-400 volts of the flash capacitors for power, this appears on the flash trigger lead; no extra wiring was involved, you just plugged the flash into the trigger unit and the main flash would set them all off.
Anyone out there have a circuit for such a beast?
crutschow said:I build a trigger for my old flash unit a couple years ago that has a couple hundred volts on the trigger. I wanted to fire it from my digital camera which couldn't tolerate the voltage thus I built the trigger. It consisted of a photodiode, an SCR, and a couple resistors and a cap. As I recall, the circuit was about as attached. I'll look further to see if I can find the exact circuit I used.
View attachment 18702
The high voltage charges the cap to about 20V. When the primary flash fires it causes the phototransistor to conduct which triggers the SCR which, in turn fires the slave flash.
I have the phototransistor looking through a small hole in a small light tight box, which contains the circuit, to minimize ambient light. You may have to experiment somewhat to get the desired sensitivity.
crust said:I'll look for it for you. Rolf, I am pretty sure that is how the other one worked. It stole a tiny amount of power from the flash and IIRC was using an IR filtered photo BJT to trigger.
The camera I used had the ability to turn off the pre-flash so I didn't need a counter circuit. I've had several P&S cameras where you could turn off the red-eye so I didn't relalize that was a problem.Rolf said:How does this unit trigger on the last flash?
Lesh said:Some of the old "automatic" flashes (the ones which sense the reflected flash and turn off their own flash to regulate the amount of light produced) were quite easy to convert.
I did this to vivitar flash units. You could identify these flashes by the sliding control on the front. This had a red, blue and black position. The red and blue positions opened two different sized apertures, and the black position covered the hole turning the unit into a manual flash.
Inside the flash, there was a gas discharge tube, which was triggered by its own trigger coil. When the reflected flash was picked up by the photodiode, a trigger pulse went to the discharge tube, dumping the high voltage quickly and stopping the main flash.
On these units, simply moving the trigger wire from the discharge tube, to the main flash tube converted the unit into a slave flash. The only down side was that the flash had to face somewhat towards the main flash to see the light from it.
More recently (about 2 years ago) I bought four more vivitar flashes. They no longer had the discharge tube (as I recall, there was an SCR to interupt the flash), and I had to add a transistor and a few resistors to turn these units into slaves. I have a schematic I drew somewhere.
Rolf said:I understand all of the above but what prevented it from triggering on a digital camera's preflash?
Still would like to see your schematic, hope you can find it.
Centretek said:Why on earth does everyone insist in using PICs?
This is a VERY simple device, You point the trigger at the main flash and the rigger fires the slave. No more control is needed. This type of device is readily available from camera stores. The ones I originally had were about the size of a quarter roll of nickels. They had a Fresnel lens on the front and a flash socket on the back. The whole thing was mounted on a suction pad that you stuck to the slave flash body, so you could point the trigger at the main flash and the slave flash at the subject.
Crutschow's cct is exactly the thing I need, all we want now is the type numbers of the devices.
crutschow said:The camera I used had the ability to turn off the pre-flash so I didn't need a counter circuit. I've had several P&S cameras where you could turn off the red-eye so I didn't relalize that was a problem.
crust said:I haven't found the circuit yet, and I thought the preflash was to determine the exposure. I don't know a whole lot about cameras though. My canon dslr+flash paints like a red colored hatch pattern on the target whenever you press the shutter halfway. I have no idea what that does, but it does not do any preflash.
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