How to reset SCR used for triggering camera flash

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shootfirst said:
If someone has a schematic of a similar optical trigger circuit, I'd love to see it.
Click to expand...

I was just realizing that the circuit (multi flash slave) that was shared in a previous post in this thread could possibly be modified in such a way that I could take out the counter and keep the optical trigger portions.

If I wanted to start from scratch, perhaps someone could help me pull the optical trigger portion of that circuit out and ignore the counter.

Just a thought.
 
Was looking into the reset problem this evening. Happened to have googled out this old thread
Here's what I understand from the discussion above, from other sources, and from the circuit of a simple optical trigger (SYK-3).

**broken link removed**

If we add into the wire to the hot-shoe an R and a C in parallel, the C should only let through current momentarily. As C charges up, the current through it will quickly drop. R should be large enough to allow through a current less than the thyristor's hold-current. Hence the thyristor will be cut off due to insufficient current, and R will discharge C into heat.

From the current through an R-C circuit (this R is the resistance of the flash as seen by the trigger, not the one in parallel), we know that having chosen R to be large enough, C will determine how quickly the current will fall, hence how quickly the thyristor will be turned off.

I may be terribly wrong - do correct me
 
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SCR reset........


I have made many optical slave flash triggers units for photographers using Canon EX type flash units. All I have to do is to replace my units normal SCR with a high voltage transistor.
Problem solved!
 


The Canon flashes are only putting about 4.5 volts in the trigger circuit. 20 year old flashes used to put 350-400 volts on those contacts (ala Vivitar 283 - 285). those voltages would kill a digital camera. The 10ufd non polarized capacitor ought to be just fine.
 
Hopefully the person with the problem found the solution five years ago and isn't still waiting.
 
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