optical slave trigger

Discussion in 'The Projects Forum' started by ellyelisa, Jan 21, 2014.

  1. ellyelisa

    Thread Starter New Member

    Jan 20, 2014
    I am trying to clone 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(s?) to control the sensitivity of the photodiode and an RC circuit to cut off exhisting ambient light, so I set it like this [​IMG] but Im not sure its right and I would need your help with that.
    If cloning is a nono on the board, could you just explain me why using resistors of such high value? seem quite big at 30M in serie (in the orange one can be seen in series)... or are they there to protect the tiny SCR from older flashes with really high voltage?
    Also, what i placed as R1+R2 should lower the sensitivity of the photodiode (thats why i cant undertand why they are that big), since in the dark the sensitivity would be high but, outside during the day, the photodiode would saturate, I was thinking I could use a potentiometer instead, or even just a couple of resistors of higher and lower value and a switch to change the resistance depending on situations. Would an inductor instead adjust all by itself increasing resistance the more the photodiode charges with the different ambient light but not be fast enough to interfere with detection of a flash?

    PS: other projects that I have seen online have a parallel RC between the SCR and the positive contact but Im not sure of whats the benefit of it, if its for the slave unit or just because the unit its using power from the strobe
    Last edited: Jan 21, 2014