I'm trying Project 15 from the Arduino Uno Projects book (optocoupler).
I manage to turn on and off a LED in a separate circuit using my Arduino-driven optocoupler.
Now I tried to also turn on some real device (battery-driven toy from my kid that she doesn't used anymore). Replacing the toy's original switch with jumper wire leaves it running, so I'm confident that it basically works. But putting my optocoupler in between, it just won't fire up.
Measuring resistance on the 4N35's output bins as advised here, I obtain -15k Ohm (and 1 when measuring the other way round, i.e., as if there were no connection at all). Switching wires also exactly switches the measurement, i.e., I never obtain any positive resistance measurement.
What can go wrong here? What else can I try to find out what's wrong? Thank you!