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.

Question:

• What is the cause of the signal drop?
• How to prevent it ? (may be logic level converter ?)

Thanks in advance !

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.

Question:

• 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 !