06-01-2025, 08:35 AM
I've confirmed that this is in fact the problem, the external device (which is a black box, I can't see the insides) has a pullup or something similar on it which puts a small voltage across the output pin. This means that the output LED is lit even when the output is off.
Is there any reason why the output-on LED is set up to indicate the presence of a voltage on the output pin rather than being between the optocoupler and the MOSFET, so actually indicate whether the output is on? Putting it before rather than after the MOSFET switch would avoid issues like this.
Is there any reason why the output-on LED is set up to indicate the presence of a voltage on the output pin rather than being between the optocoupler and the MOSFET, so actually indicate whether the output is on? Putting it before rather than after the MOSFET switch would avoid issues like this.