I'm trying to get the status of my set top box (on/off).
It does have USB but it's always powered on.
It has optical out that is also always on.
It has an IP address that always responds to ping.
So my next idea is to read the signal in the SCART.
If I read the voltage across pin 8 and 14 I get 0-ish when off and 12 when on.
But when it powers on it spikes at 18 volt (at least what my multimeter can see).
What do I need to do to read this?
If I add a voltage divider with 1 and 4.7 Kohm I get a safe voltage if it does not go above 18 volt at any time.
But what can I do to be sure I don't burn a ESP chip?
Is there any way to make sure it's safe to read even if it spikes at say 25 volts?