"Exactly how is the signal generator connected to the Arduino?"
"Is the signal generator's ground connected to the Arduino's ground?"
-the signal generator connected to the arduino at pin 8 and also the ground of the arduino.
"What is the voltage of the signal generators output?"
-i put voltage output from the signal generator is 30V peak to peak
"What is the power frequency at your location?"
-my location is australia and i check from the website, it say that 50 Hz. Is it the reason why my output 49-51Hz. means the arduino not reading the signal at right right
"I can't tell, but I think that you might have connected a resistor to pin 8. What was the value of the resistance? What was the other end of the resistor connected to?"
yes, i connected the resistor and the value i used as you suggested which is 100k ohm. i connect the resistor to pin 8 and the other to ground. and i also tried to Vcc as well. the output still the same
by the way, how i can make quote only for certain sentence. its like when i click insert the quote, they quote everything.