I don't know what's wrong... I have an ATTiny13 which gives a dummy impulse turning a fan on and off every 2 seconds; so the plan.
I attach two power sources (for dummy purpose) before and after the optocoupler (5V on the top right; and DV on the center bottom). In the experiment both have 5V but it has to be tested like this.
When I put an LED behind the opto instead of the fan, it shines bright and nice. When I replace it with the fan - you see it trying to move but without enough power so he just move 1mm until the power goes off again.
I just circled the optocoupler part.
It would be very nice if someone has a clue why there is such a voltage drop through the optocoupler.