Sensor and Arduino code

/*
 Magsensor

 Magnetic proximnity sensor for bell simulator.  

 */

// constants won't change. They're used here to
// set pin numbers:
const int sensorPin = 2;    // the number of the proximity sensor signal pin
const int ledPin = 13;      // the number of the LED pin

int sensorState = LOW;

void setup() {
  Serial.begin(2400);

  pinMode(sensorPin, INPUT);
  pinMode(ledPin, OUTPUT);

  // set initial LED state
  digitalWrite(ledPin, LOW);
}

void loop() {
  // read the state of the switch into a local variable:
  int reading = digitalRead(sensorPin);
  digitalWrite(ledPin, reading);

  if (reading != sensorState) {
    sensorState = reading;
    if (sensorState == HIGH) {
      Serial.print("1");
    }
  }
}

Parts:

KY-024 Hall effect sensor (£3 – £4)

neodymium magnet (can be salvaged from an old hard drive)

epoxy glue to attach magnet to wheel

Arduino Uno (£20)

Male to Female Jumper Cables

USB device cable and extension cable