I have a 4KHz 5V pulsed signal connected to Arduino UNO pin2 (ISR).
When the board is powered, the pulse is attached to ISR rising edge, and is working as intended.
I don't know the output impedance of the pulsed signal, but when the board is not powered, the pulse drops to 2V.
The resistance between pin2 and ground is about 500K when not powered. The resistance is infinite when powered.
The pulsed signal does NOT drop when connected to a 500K resistor.
- What is the cause of the signal drop?
- How to prevent it ? (It's not practical to disconnected the signal from Arduino, but I can make sure Arduino is always powered. How to deal with transient situations like reset ?)
Thanks in advance !