I've never encountered optocoupler before. However, in a small project I'm developing, their usage is recomended. I've connected the components as shown in the attached diagram, but I can't seem to activate the LED (it's there temporarily until I solve the issue of current flow through the optocoupler). Can anyone advise me on what might be the specific issue in this case?
If "D1" is the LED to which you refer, check polarity. Short circuit the pins 4&5 on the optocoupler to activate it.
Did you solder connections to all pins, correctly?
Is digital pin 3.3V or 5V?
What is the Vf of D1 LED?
Apart from the other suggestions, maybe that opto coupler just doesn't have the "strength" to drive an LED?
That's not usually what opto couplers are used for: they're usually just for isolating signals - not driving loads like LEDs ...
There should be a "current transfer ratio" or similar spec in the datasheet.
Are you sure that the LED is the right way around. Long leg usually positive (anode). Flat on body of LED negative (cathode).
LED polarity is OK. I tested all pins with multimeter diode check mode. It looks fine. I returns 900-950 units on pins 1&2 and none on 4&5.
It is still on breadboard
Check for bad breadboard connections. Breadboards are unreliable and intended for tests with temporary circuits.
It is Arduino Pro mini, 5V. Tested several different diodes. In the case of red LEDs, Vf= 1.8
Again:
You could test that by replacing D1 with a current meter (DMM on current range) - do you get any current at all ?
Try it first on the milliamps range; if you don't see anything, the more sensitive ranges...
This is just a simplified drawing used to explain the problem. In reality it uses 12V source. I tested this scenario in Proteus simulator and it works. I exhausted all possible ideas and that's why I have to as for help.
The diagram is correct.
The LED should light up, independent of CTR.
Even a low CTR of 10% will still light the LED brightly (with 1.5mA).
Could be a build problem, or you forgot to set the pin to OUTPUT, or a faulty opto (unlikely).
Post a picture if the setup.
Leo.
Your circuit looks good to me and I would expect it to work, even if the LED lights-up dimly.
Did you try that?
Have you tried another opto-coupler? Maybe it's simply bad...
That's on the LED side, right?
Is anything else different from reality?
Are you sure about the resistor values? i.e. It's not going to work with 220K resistors.
Did you try that?
This is just a simplified drawing used to explain the problem.
We can't help you debug your circuit if you don't show us what you are actually doing.
In reality it uses 12V source.
That puts it very close to the maxium power dissapation. Maybe you burned it out.
Proteus simulator and it works.
It won't tell you if you exceeded the part specifications.
Yes, it is correct, no doubt. Arduino pin gives 5V on output so it is not the cause. I also tried connecting 5V from power source on pin 1, no difference.
That will burn out the optocoupler.
So will 12V
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[quote="DVDdoug, post:13, topic:1165229, full:true"]
Did you try that?
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In what sense to activate it?
I've got 20 pcs, tested them all and two were bad
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Of course, 12V should be on the LED side, Instead of it I plan to use a small motor but I firstly need to get output from the optocoupler,
Absolutely, I tested it with multimeter
My apologize, I'm on holidays now so I can't give you more details. I just wanted to get an output voltage on optocoupler. That's why I put this simplified scheme instead of more difficult one.
probably I wasn't clear enough,12V should be on the output side but not in this test case. For now, it is 5V only,
I forgot to say about the resistor 
What motor, and what is it's stall current.
Opto couplers are for small signals. A 10mA LED a the most.
The opto transistor will burn out if you try to switch a motor with it.
Simulators don't give you that information.
Leo..
Please try to be sober when using [quote]...