Use a potentiometer on analog port A0 . vary the pot and read the voltage and dispaly it on serial monitor
Code
/*Paste your code here*/
void setup() {
// put your setup code here, to run once:
Serial.begin(9600);
}
void loop() {
int signal;
// put your main code here, to run repeatedly:
signal=analogRead(0);
Serial.println(signal);
delay(50);
}