Is it possible to use the ADC and the DAC of the atmega328P in order to output a signal exactly as the input signal? In other words, making an exact copy of a waveform using the ADC to read the input signal and copying it and then using the DAC to output another copy.

Please note that the signal intended to be copied is not just 5V and 0V.

Not exact, no. The ADC has 10 bits of precision and only about 9 bits of accuracy, so that will introduce some distortion. You would also have to use a low-pass filter and would lose any frequencies under about half the frequency of the ADC sampling rate, probably more like a quarter, practically speaking.

Do you really need exact? Technically even a plain wire won't allow an exact copy.

Plus an ATMEGA328P doesnt have a DAC that I know of.

Well, that's probably true. But what I'm trying to do is, let's say the input signal is a 15Hz sine wave. The output (from another pin other than the input pin) should have the same frequency and amplitude, after "copying" the signal...

The chip doesn't have any analog output pins. The best you could do is PWM and a low-pass filter, or an external DAC.

lcruz-

Don't copy the signal through the MCU, simply use the MCU to analyze the signal. Use a transistor to copy the signal based on the MCU's analysis.

BM