i'm trying to fire a studio strobe (an old profoto to be exact) using an arduino and optocoupler. i have 2 of them and can't seem to get either to fire the strobe consistently.
a NTE3086
and a
4N28
right now i have the NTE3086 on the breadboard. i've used this to fire off a canon without using any resistors and it worked a.o.k.. this time i tried to calculate and come close to what resistor i thought it needed using a resistor calculator (51 ohms).
i hooked up a test LED to confirm that it was firing correctly and it was... did a test similar to Loading...
but when i hook it up to a stereo cable that connects to a PC Sync cable it is only firing 1 out of every 3 or 4 shots. i've adjusted the how long the signall gets sent from 10 millis to 100 millis to see if that made a difference and so far it has not.
i hooked up a multimeter to the PC sync coming from the strobe and i'm getting a reading of 27.8 DC volts and 115.2 milliamps. the specs on the NTE3086 look as if it can handle up to 30V is that correct? does anyone have any ideas as to why it would be firing sporadically?
Maybe you're just not providing enough current for the strobe to fire reliably?
A single Arduino pin can source out ~40mA and the NTE3086 has a Current Transfer Ratio (CTR) of 50% @ 10mA, according to the datasheet. It's hard to guess what is the output current @ 40mA, but it's probably way less than 115mA. You should be able to measure it.
To get more current on the output, you need another transistor. Either add an external one or get an optocoupler with a Darlington pair on the output~~. For example - 6N138?~~
P.S. This 51 ohms resistor seems to be of no practical use. At 5V, it is "limiting" the current to 70-75mA, which is more than the 40mA a pin can provide.
I use MOC3020 opto triacs to trigger old Vivitar 283s.
The great thing is, you don't have to care about polarity on the output.
Depending on age of the unit, trigger voltage can be between 6 and 180 volts.
LEDs in parallel is not usually a good idea. Maybe these are matched enough. Better they go in Series.. So if LED voltage is 2.1 + 2.1 (maybe) that's 4.2 so not much drop left to 5.0 (or really more like 4.8V) so maybe resistor could be your 51 ohms you had before?? Maybe 0.6/.02 = 30 ohms or so? 27 if you have one...
The outputs in parallel probably is why it works now...
In the long run the opto-triac is probably a lot better solution....
Have you measured the voltage at the jack, I bet this is much greater than 30V, normally on the flash guns I have seen this is more like in the region of 80 to 120V.
I would also recommend and opto-triac or even an opto FET. Often FETs are much better at recreating a closed contact than transistors are. I have triggered camera shutters with FETs when they wouldn't work with transistors.
If you do have LEDs in parallel they must have their own current limiting resistor and the total current from the arduino pin must be below 40mA.
See:- http://www.thebox.myzen.co.uk/Tutorial/LEDs.html
