wvmarle:
So what is the exact nature of this input signal? You only mentioned analogue and 5 kHz.
Signal 1 is from telephone line...300Hz - 5000Hz,
Signal 2 is a signal produced by the Arduino...
Also, I want to ask this: If I set a pin of Arduino nano as OUTPUT, and I send 5 Volts to this pin from another circuit, could I cause any damage to the Arduino/pin?
Thank you...