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?

__________________
A conclusion, is the point reached when you stop thinking.

 

Centretek, I might have a circuit like that, I would have to look around. I know what you are talking about. The main reason they seem hard to find now is that most flashes have a low voltage interface to the camera. Just to be sure we are thinking the same thing, you are referring to an optical slave, correct? I.e. not the kind that are hard wired to a shoe-adapter type thing.

 

Hi Centretek,

don't spend unnecessary money for a simple circuit. Here is the example of a "Tochterblitz" (Tochter=daughter and blitz=flash) "Mother" flashes first and "daughter" follows right away.

If you are interested I'll translate the entire article for you and will also supply the PCB layout. Just PM me.

Compared to the ones I used this circuit is really huge.

May be you are interested in my electric power fence too?

Kind regards

Hans

 

Crust, you are exactly on the money. The old cheapy flash units are still available from goodwill stores and garage sales. They are really inexpensive and we don't want auto metering etc.They are only for rim and backfill lighting.
If you can find the circuit and component values I would be extremely grateful.

Boncuk, sorry, that's exactly what I don't want. It requires a separate battery and is too complicated. I need to make them for a few bucks each. A studio kit needs 6-8 of the little buggers.

__________________
A conclusion, is the point reached when you stop thinking.

 

The circuit for using the flash trigger voltage to power the slave flash trigger must be a closely held secret. How do you steal enough power to operate the slave flash trigger, without triggering it? My Vivitar 2500 flash units trigger voltage is only 12.5V.
I have meant for some time to establish how much of a load I can put on it before it triggers, I'll try to get around to it soon.
The PIC based units are much simpler than the previous posted unit, here is mine: http://www.diyphotography.net/very_c...cal_slave_unit
Granted it uses a 3V battery but you can wire many flashes to one by using isolating diodes.

Edit: Just checked my three Vivitars, the 2500 was the most sensitive and the only one I checked closely. A 27K resistor triggers it but not 32K, so it seems like you could draw almost 0.4mA from the circuit, plenty enough for a PIC.

 

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.

 

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.
Flash Trigger.gif
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.

 

How does this unit trigger on the last flash? Most simple circuits trigger on the preflash and are therefore useless, because most P&S cameras have no way of turning OFF the preflash.
There are lots of slave flash triggers of different types with circuits posted on the Internet. Some count flashes, some use timing circuits and one triggers on the last flash after being taught, like this one: http://www.pbase.com/sinoline/sft_kit
But they have one thing in common they use batteries.

 

The problem as I see it is that you need a regulator that doesn't draw over 0.35mA and can handle 12.5V to about 300V input, with a fairly clean 3V output at about 0.30 mA.

 

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.

 

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.

 

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.

 

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.

__________________
A conclusion, is the point reached when you stop thinking.

 

Forgot to look for the circuit yesterday. I'll try to check tonight.

 

The most recent batch is used with a DSLR (Nikon D100) which does not have the pre-flash. The older batch was before cameras with preflash.

I will look for the schematics I made.

I wonder, what the preflash for: Is it for the camera to calculate exposure, or is it designed to reduce "red eye" by dilating the subjects pupils before the picture is taken?