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optical slave trigger

Discussion in 'General Electronics Discussion' started by Elisa, Jan 19, 2014.

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  1. Elisa


    Jan 19, 2014
    I am trying to replicate this optical slave trigger [​IMG] (btw the two circuits in the picture are the same, one is part of the hotshoe while the other has a plug at the back to be attached to a strobe or an hotshoe)
    I suppose that there are a resistor(i to control the sensitivity of the photodiode and an RC circuit to cut off the ambient light to use it outside so i set it like this [​IMG] but Im not sure its right because the resistors value seem quite big at 30M (R1+R2, in the orange one can be seen in series)... i would have thought that even the 4.7k would be too much

    PS: other projects i have seen online have a parallel RC after the SCR but Im not sure of whats the benefit of it
  2. Arouse1973

    Arouse1973 Adam

    Dec 18, 2013
    What's a hotshoe?
  3. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    Jan 21, 2010
    It's the thing an on-camera flash is attached to which acts to trigger the flash.

    c.f. cold shoe - that's what's on older cameras which used a separate cable to trigger the flash (typically a PC Sync cord).
  4. davenn

    davenn Moderator

    Sep 5, 2009
    obviously not a photographer ;)

  5. Elisa


    Jan 19, 2014
    maybe i should clarify:
    as said before, hotshoe is what provides attachment and electrical contacts for the flash on a camera, also its referred to the "cube" (for lack of better word) used to bring the contacts to a flash positioned away from the camera, in this you would find the attachment for the flash like on a camera, the attachment for a tripod or other support and one or more plugs to attach sync cords that would physically connect it to the camera for triggering and passing other informations, other ways to trigger the slave flash is through radio, or optical like in my case. The black cube you see in the picture is an hotshoe adapter with an integrated optical slave circuit, the flash on the camera shoots and the optical sensor sees it and triggers the remote flash attached to it, basically at the same time.
    In the simple hotshoe, without other frills, the rails are ground and the center pin is the positive, in the flash these are active, and thats where current for the optical slave is taken, connecting the rails to center pin will trigger a flash to shoot. Old flashes can discharge over 250/300 V at the hotshoe (thats why they cant be used on digital cameras as they are) newer flashes are in the order of 3 to 5 V at the hotshoe.
    A simple version of the circuit is a photodiode attached to a SCR, but ambient light would trigger it, outside during the day the light would saturate the photodiode etc, so its necessary to filter the ambient light and correct the sensitivity. In the circuit Im trying to copy Im not sure i got the connections right using those components. i seem to read the capacitor is 0..047
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