I've got a cheap drop bolt lock and I would like to detect whether it's internal reed switch is on or off (current is flowing or not) without modifying the lock itself or adding another reed switch. Is it possible? If so how?
Simulated circuit, I've also attached an image of this simulated circuit.
Use two 10k's in series from that point to ground. The centre tap will be close to 0V if the reed is open or if
the transistor is on, otherwise about 6V (OK for Arduino due to 10k being in series with it).
I think the middle will be 5.5V due to the action of the input protection diode clamping the line to Vcc (Vcc + 0.5v).
When the MOSFET is driven, the signal will go low. Otherwise it will be high.