Pitch follower using the tone() function

This example shows how to use the tone() command to generate a pitch that follows the values of an analog input. Using a photoresistor your Arduino board becomes a simplified light theremin.

Hardware Required

  • Arduino board

  • 8 ohm speaker

  • photoresistor

  • 4.7K ohm resistor

  • 100 ohm resistor

  • hook-up wires

  • breadboard


arduino speaker photocell bb

Connect one terminal of your speaker to digital pin 9 through a 100 ohm resistor, and its other terminal to ground. Power your photoresistor with 5V, and connect it to analog 0 with the addition of a 4.7K resistor to ground.


arduino speaker photocell schem


The code for this example is very simple. Just take an analog input and map its values to a range of audible pitches. Humans can hear from 20 - 20,000Hz, but 120 - 1,500 usually works pretty well for this sketch.

You'll need to get the actual range of your analog input for the mapping. In the circuit shown, the analog input value ranged from about 400 to about 1,000. Change the values in the map() command to match the range for your sensor.

The sketch is as follows:


  Pitch follower

  Plays a pitch that changes based on a changing analog input


  - 8 ohm speaker on digital pin 9

  - photoresistor on analog 0 to 5V

  - 4.7 kilohm resistor on analog 0 to ground

  created 21 Jan 2010

  modified 31 May 2012

  by Tom Igoe, with suggestion from Michael Flynn

  This example code is in the public domain.



void setup() {

  // initialize serial communications (for debugging only):


void loop() {

  // read the sensor:

  int sensorReading = analogRead(A0);

  // print the sensor reading so you know its range


  // map the analog input range (in this case, 400 - 1000 from the photoresistor)

  // to the output pitch range (120 - 1500Hz)

  // change the minimum and maximum input numbers below depending on the range

  // your sensor's giving:

  int thisPitch = map(sensorReading, 400, 1000, 120, 1500);

  // play the pitch:

  tone(9, thisPitch, 10);

  delay(1);        // delay in between reads for stability

See Also

Last revision 2015/08/11 by SM