Arduino includes this example, find it under: File > Examples > 3.Analog > Analog Input

Then compile and upload it to your metro. Tweak the potentiometer to change the LEDs brightness. 

If you are having trouble finding or loading the example, the code is below:

  Analog Input
 Demonstrates analog input by reading an analog sensor on analog pin 0 and
 turning on and off a light emitting diode(LED)  connected to digital pin 13.
 The amount of time the LED will be on and off depends on
 the value obtained by analogRead().

 The circuit:
 * Potentiometer attached to analog input 0
 * center pin of the potentiometer to the analog pin
 * one side pin (either one) to ground
 * the other side pin to +5V
 * LED anode (long leg) attached to digital output 13
 * LED cathode (short leg) attached to ground

 * Note: because most Arduinos have a built-in LED attached
 to pin 13 on the board, the LED is optional.

 Created by David Cuartielles
 modified 30 Aug 2011
 By Tom Igoe

 This example code is in the public domain.


int sensorPin = A0;    // select the input pin for the potentiometer
int ledPin = 13;      // select the pin for the LED
int sensorValue = 0;  // variable to store the value coming from the sensor

void setup() {
  // declare the ledPin as an OUTPUT:
  pinMode(ledPin, OUTPUT);

void loop() {
  // read the value from the sensor:
  sensorValue = analogRead(sensorPin);
  // turn the ledPin on
  digitalWrite(ledPin, HIGH);
  // stop the program for <sensorValue> milliseconds:
  // turn the ledPin off:
  digitalWrite(ledPin, LOW);
  // stop the program for for <sensorValue> milliseconds:

Not Working?

Sporadically Working

This is most likely due to a slightly dodgy connection with the potentiometer's pins. This can usually be fixed by taping the potentiometer down.

Not Working?

Make sure you haven't accidentally connected the potentiometer's wiper to digital pin 0 rather than analog pin 0. (the row of pins beneath the power pins)

Still Backwards?

You can try operating the circuit upside down. Sometimes this helps.

This guide was first published on Aug 18, 2017. It was last updated on Jul 18, 2024.

This page (Code) was last updated on Jul 18, 2024.

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