erik
Regarding solution 1: maybe I was not clear enough, but we are already having issues when trying to drive 2 cameras. The issues I described were happening when testing 2 cameras, not 4. Out of the two cameras that I am trying to synchronously trigger with the transistor:
- one does trigger, but the image occasionally flickers (it looks as if it were overexposed)
- the other one does not trigger at all
As for solutions 2 and 3, what is the logic behind them? Reducing the current through the input of each camera's optocoupler in case the transistor cannot supply enough current to trigger them both? Wouldn't solution 3 involve opening up the cameras and desoldering an SMD resistor (and also soldering a new one in the case of R12)? I would definitely like to avoid this and would prefer to design a new circuit that works with the cameras directly.
For this however, I would like to understand why my current circuit is not working, so that I can avoid making the same mistake again. If my calculations are correct, the BC517 should be capable of supplying plenty of current to trigger 2-4 cameras. It has a minimum gain of 30000, which means that for a base current of ~16uA (set by the 120k resistor), we should be able to get up to 475mA of current through the collector while operating in saturation. Considering a max V_CE(sat) of 1V, and a typical forward voltage of the LTV-356 of 1.2 V, we should have a 9.8V drop through the 2x 4.7k resistors in parallel, leading to a 4.2mA current per camera. With 4 cameras in parallel it would be 16.7mA, far from the theoretical maximum of 475mA.
There is another issue that I don't think is addressed by any of the solutions: the flickering of the images of the camera that is actually triggering. Could this be caused by a trigger signal that is of a frequency that is not stable enough? If so, what kind of frequency accuracy do we need in order to avoid flickering?