Hi,
I want to connect 4 4N25s (or 4N26s) together to form a trigger signal multiplier (1 in, 4 out).
In will come from an Arduino pin.
Are there any special considerations?
I plan to connect in series. Is this OK?
Thanks
MartynC:
Hi,I want to connect 4 4N25s (or 4N26s) together to form a trigger signal multiplier (1 in, 4 out).
In will come from an Arduino pin.Are there any special considerations?
I plan to connect in series. Is this OK?Thanks
What value resistor do you intend to use for current limiting?
Paul
What current is needed through the opto transistor.
According to the datasheet, min CTR is 20%.
If it's low, you could run two strings of two opto LEDs from one pin.
Each with their own CL resistor (<=10mA/string).
If you need more LED current, and external transistor is needed.
Leo..
MartynC:
to form a trigger signal multiplier
What does that even mean?
I'm guessing xy problem.
Hi,
Can you please post a copy of your circuit, in CAD or a picture of a hand drawn circuit in jpg, png?
What is the application?
Tom.... 
I have Fairchild 4N25s. Current is 10 mA.
Here is a link to the circuit I am thinking of using.
As per Wawa's suggestion. I now have 2 sets of 2 optocouplers.
I have 330 ohm resistors in the diagram and I believe I can go to 100 ohm based on 2 LEDs at 10mA each (please correct me if I am wrong).
The application is a flash trigger multiplier. I want to trigger 4 flash guns from a single Arduino pin.
At present I use 4 identical flash guns and connect them using headphone splitters. This means all the flashes are connected to each other. I believe this is OK since all the flash guns are identical and have a fairly low trigger voltage of 3.3v.
I would now like to mix flashes with slightly different trigger voltages and so think I should not connect them together.
What's the voltage from D12 to ground?
MartynC:
I have Fairchild 4N25s. Current is 10 mA.
An opto coupler has gain or loss (CTR or Current Transfer Ratio).
You look at the current the opto transistor has to switch, and then calculate opto LED current needed.
A 4N25 has a minimum CTR of 20%, meaning 10mA LED current is enough to switch 2mA or more.
Flash trigger current is unknown, so try 10mA opto LED current.
That means one Arduino port can drive four LEDs the way I have explained in post#2.
I said two strings (like Christmas lights, in series).
Pin > 220ohm resistor > anode first opto LED > cathode to second opto LED anode > second cathode to ground.
This string of two opto LEDs draws ~10mA.
Arduino pin limit is ~20mA, so a second string of two can be connected to the same pin.
Leo..
Thanks for all the help.
Just measured the current across the trigger pins on one of the flash guns. It is 950μA / ~1mA.
Here is, hopefully, the final circuit.
Yes, that should work.
+1 for the neat diagram, and for posting back.
Leo..