majenko:
If that is so, then connect the green to +5V, the black to GND, and the white to A0. Read from A0 to get the position of the cog.
Perfect, with this code :
/*
AnalogReadSerial
Reads an analog input on pin 0, prints the result to the serial monitor.
Attach the center pin of a potentiometer to pin A0, and the outside pins to +5V and ground.
This example code is in the public domain.
*/
// the setup routine runs once when you press reset:
void setup() {
// initialize serial communication at 9600 bits per second:
Serial.begin(9600);
}
// the loop routine runs over and over again forever:
void loop() {
// read the input on analog pin 0:
int sensorValue = analogRead(A0);
// print out the value you read:
Serial.println(sensorValue);
delay(1); // delay in between reads for stability
}
All right, now you pick the place where you want me to kiss you 
So I can use this stuff !
Kind of never ending potentiometer to me !
Or i could it to count how much turns something have done.
From 0 to 1023 with for one complete turn, some glitches after ~ 350 degre to 0, then that start over from 0 to 1023 ...
Muchas gracias !