Hello,
I have an issue with reading a device status. I have a device with LED that is on when it is operational and off when it is not. This is the moment where it stops being so common. Inside the device I have found a point that changes its value depends on the device status - it is 5V when it is off and 3.5V when it is on. I have S2 Mini that is paired with octocoupler and detects that 5V state but the problem is that it is not changing its status when device goes on and start hahing 3.5V. ATM optocoupler (PC817) is paired with 220ohm resistor.
Two ways I havetried is to find a resistor that makes PC817 works when 5V is present and not when 3.5V appears. That failed (looks like lower limit of 5V is good enough like upper limit for 3.5V).
I have thought about ADC value measurement (optionally with voltage divider) but then I do not have circuits separation.
What else could be done? High pass voltage filter? Thinking about placing 2-3 diodes like 1N4001 in series - this should lover voltage enough to make distinction between states. Any other ideas?