Homemade flash trigger

Discussion in 'Lighting Equipment' started by royall_berndt, Jan 5, 2021.

  1. I used to see plans in.magazines for constructing flash triggers. Anyone have those plans?
  2. I have no idea what type of trigger in that magazine but I have seen other optical trigger using Light Activated SCR.
  3. The magazine trigger used an LA SCR.
  4. Good luck finding one of those these days.

    I built an opto-slave years ago using a photodiode, a transistor and a low gate current SCR. Plus a couple of resistors, a zener diode and a capacitor to power the thing from the flash trigger voltage.

    These days it would cost more in components, connectors and a transparent housing than you could buy one for.

    Sunpak and other makers sold little 'peanut' slave triggers with a rubber sucker for mounting. They're quite plentiful and crop up for sale quite regularly and cheaply.
  5. Afraid Joe hit the nail on the head. I had the same idea years back and couldn't find a LASCAR or LA SCR anyplace.
  6. As far as I know, this is the favorite use for LASCRs.
  7. I came across my old homemade slave trigger the other day. So for the sake of completeness; here's a picture of it and its CCT diagram.
    And the circuit -
    The MRD14B is a photo-darlington transistor. Good luck finding one of those these days! As well as sourcing a C-106 sensitive gate SCR... or a small transparent plastic box... or a male line P-C plug.

    I suppose a photo-darlington could be fabricated by cutting the top off a metal TO-18 cased device and filling it with transparent epoxy resin. But really, is it worth the cost and trouble?

    Unless constructing junk-bin electronics is your idea of fun.;):rolleyes:

    Oh, nearly forgot. The circuit was designed to be 'self-powered' using the small current available from an old high trigger voltage flash. Hence the 1.5 megohm resistor. With a modern low trigger voltage flash that resistor could be replaced with a much lower value, or even with a short. And any consequences from using the above design are entirely at your own risk. I take no responsibility!
    Jochen likes this.
  8. I think you can now get photo-SCRs, so maybe no need for photo-darlington

    My first real electronics project, real enough to get in a box, is (I still have it somewhere) a touch switch from Popular Science.

    It uses the C106B1, which looks like the one you have. I built that in about 4th grade, after mail ordering the SCR and the NE-83 from Allied Electronics.
  9. Otherwise, you get the reverse PC from a PC extension.

    I still have the PC cord for my Vivitar 283. One could cut off the PC end, and splice directly onto the rest of the cable.

    Or splice directly onto a hot-shoe to PC adapter.
  10. Last edited: Aug 5, 2021
  11. The touch switch is in this one:

    Popular Science

    I used a regular box, though, and then built a new box for it in
    metal shop in 7th grade.

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