Sorry that I am being such an annoyance, but I have another question. I dont
want anyone to go through the trouble of providing an entire circuit. In
fact I want to do it myself. I just wanted to be pointed in the right
directions. What parts do I research, etc.

Anyway, here is the problem. I want to electronically trigger a photo flash
of unknown trigger voltage. The flash provides the voltage. The circuit
simply needs closed to fire the flash. But here is the trick. Photo flashes,
especially older ones, have a wide range of trigger circuit voltages. At the
low end it could be only 3.5v. On the high end it could be 300v. I have 3
flash units. (3.5v, 15v, and 55v) Although I read that there are a few old
units that go 100v and higher. Much above 5v can be death to a modern
electronic camera. So I want to make a circuit such that I can use any of
mine, and maybe other, flash unit with a electronic camera. (Either mine or
a friend's.)

So, what kinds of componets do I research that can give me the ability to
trigger a flash with a range of 3.5 to, say, 100v? I have done a search and
found high voltage transistors that can handle 200v (collector to emitter)
but still only need 5v at the base. Someone has mentioned looking into
something called an SCR. That same person suggested an opto-isolator for
best possible protection of the camera. What about a voltage regulator? (I
might be using someone else's $1000+ digital camera, so I want to be extra
carefull. Last thing I want to do is to return to them a fried camera.)

I have found sites discussing the theory of some of these components, but
they dont really give the practicle trade-offs as to when you might want to
use one verses another. Again, I am not looking for an exact circuit, just
an idea what to best spend my energy researching.

Thanks in advance,
Henry