thank you very much for the reply.
that's a good idea of the voltage drop of the diode. i almost forgot that..
I think i will handle the programming of this. I won't stop till it work..
Im worried of my setup that it won't work.
But because you said it would possibly work, I will try it later this day.
i am thinking of an input of a Function Generator that gives a sine wave that has maximum of + and - 3 volts peak.
I just want to show my instructor that arduino can also read negative voltages.
A question about the input impedance or current capability, is this very strict?
Do i need to put resistors to balance their impedance?