This example demonstrates one techinque for calibrating sensor input. The Arduino takes sensor readings for five seconds during the startup, and tracks the highest and lowest values it gets. These sensor readings during the first five seconds of the sketch execution define the minimum and maximum of expected values for the readings taken during the loop.

(:source http://arduino.cc/en/pub/code/master/build/shared/examples/03.Analog/Calibration/Calibration.ino lang=arduino tabwidth=4:)

(:source http://arduino.cc/en/pub/code/master/build/shared/examples/3.Analog/Calibration/Calibration.ino lang=arduino tabwidth=4:)

(:source http://arduino.cc/en/pub/code/new-extension/build/shared/examples/3.Analog/Calibration/Calibration.ino lang=arduino tabwidth=4:)

(:source lang=arduino tabwidth=4:)

(:source lang=arduino class=code tabwidth=4:)

(:div class=BOM :)

(:divend:)

(:div class=circuit :)

(:divend:)

(:divend:)

(:div class=code :)

(:div class=code :)

Here's the whole program:

 // calibrate during the first five seconds 
 while (millis() < 5000) {
   sensorValue = analogRead(sensorPin);

   // record the maximum sensor value
   if (sensorValue > sensorMax) {
     sensorMax = sensorValue;
   }

   // record the minimum sensor value
   if (sensorValue < sensorMin) {
     sensorMin = sensorValue;
   }
 }

Calibration

• If()

Attach:calibration2_sch.png Δ Δ

This way, any further readings you take can be mapped to the range between this minimum and maximum like so:

 Here's the whole program:

This example semonstrates one techinque for calibrating sensor input. The Arduino takes sensor readings for five seconds during the startup, and tracks the highest and lowest values it gets. These sensor readings during the first five seconds of the sketch execution define the minimum and maximum of expected values for the readings taken during the loop.

Before the setup, you set initial values for the minimum and maximum like so:

(:source lang=arduino tabwidth=4:) int sensorMin = 1023; // minimum sensor value int sensorMax = 0; // maximum sensor value (:sourceend:)

These may seem backwards. Initially, you set the minimum high and read for anything lower than that, saving it as the new minimum. Likewise, you set the maximum low and read for anything higher as the new maximum, like so:

(:source lang=arduino tabwidth=4:)

  // calibrate during the first five seconds 
  while (millis() < 5000) {
    sensorValue = analogRead(sensorPin);

    // record the maximum sensor value
    if (sensorValue > sensorMax) {
      sensorMax = sensorValue;
    }

    // record the minimum sensor value
    if (sensorValue < sensorMin) {
      sensorMin = sensorValue;
    }
  }

(:sourceend:)

 This way, any further readings you take can be mapped to the range between this minimum and maximum like so:

(:source lang=arduino tabwidth=4:) // apply the calibration to the sensor reading sensorValue = map(sensorValue, sensorMin, sensorMax, 0, 255); (:sourceend:)

(:source http://arduino.cc/en/pub/code/master/build/shared/examples/3.Analog/Calibration/Calibration.pde lang=arduino tabwidth=4:)

• while()
• millis()
• [[Reference/analogRead}]()

Connect an LED to digital pin 9 with a 220 ohm current limiting resistor. Connect a photocell to 5V and then to analog pin 0 with a 10K ohm resistor as a reference to ground.

(:divend:)

See Also:

• [[Reference/while]()
• [[Reference/millis]()
• [[Reference/analogRead}()
• analogWrite()
• constrain()
• map()

• AnalogInput - use a potentiometer to control the blinking of an LED
• AnalogInOutSerial - read an analog pin, map the result, and use that data to dim or brighten an LED
• Fade - use an analog input to fade an LED
• Smoothing - smooth multiple readings of an analog input

Hardware Required

• Arduino board
• (1) LED
• (1) analog sensor (a photocell will do)
• (1) 10K ohm resistor
• (1) 220 ohm resistor
• breadboard
• hook-up wire

 (:source http://arduino.cc/en/pub/code/master/build/shared/examples/3.Analog/Calibration/Calibration.pde lang=arduino  tabwidth=4:)

 (:source http://arduino.cc/en/pub/code/master/build/shared/examples/Analog/Calibration/Calibration.pde lang=arduino  tabwidth=4:)

image developed using Fritzing. For more circuit examples, see the Fritzing project page

Code

(:div class=code :)

 /*
   Calibration
  
  Demonstrates one techinque for calibrating sensor input.  The
  sensor readings during the first five seconds of the sketch
  execution define the minimum and maximum of expected values
  attached to the sensor pin.
  
  The sensor minumum and maximum initial values may seem backwards.
  Initially, you set the minimum high and listen for anything 
  lower, saving it as the new minumum. Likewise, you set the
  maximum low and listen for anything higher as the new maximum.
  
  The circuit:
  * Analog sensor (potentiometer will do) attached to analog input 0
  * LED attached from digital pin 9 to ground
  
  created 29 Oct 2008
  By David A Mellis
  Modified 17 Jun 2009
  By Tom Igoe
  
  http://arduino.cc/en/Tutorial/Calibration
  
  */

 // These constants won't change:
 const int sensorPin = 2;     // pin that the sensor is attached to
 const int ledPin = 9;        // pin that the LED is attached to

 // variables:
 int sensorValue = 0;         // the sensor value
 int sensorMin = 1023;  // minimum sensor value
 int sensorMax = 0;     // maximum sensor value

 void setup() {
   // turn on LED to signal the start of the calibration period:
   pinMode(13, OUTPUT);
   digitalWrite(13, HIGH);

   // calibrate during the first five seconds 
   while (millis() < 5000) {
     sensorValue = analogRead(sensorPin);

     // record the maximum sensor value
     if (sensorValue > sensorMax) {
       sensorMax = sensorValue;
     }

     // record the minimum sensor value
     if (sensorValue < sensorMin) {
       sensorMin = sensorValue;
     }
   }

   // signal the end of the calibration period
   digitalWrite(13, LOW);
 }

 void loop() {
   // read the sensor:
   sensorValue = analogRead(sensorPin);

   // apply the calibration to the sensor reading
   sensorValue = map(sensorValue, sensorMin, sensorMax, 0, 255);

   // in case the sensor value is outside the range seen during calibration
   sensorValue = constrain(sensorValue, 0, 255);

   // fade the LED using the calibrated value:
   analogWrite(ledPin, sensorValue);
 }

(:divend:)

// variables:

int sensorMin = 1023; // minimum sensor value int sensorMax = 0; // maximum sensor value

Circuit

click the image to enlarge

Schematic

click the image to enlarge

/*

  Calibration

 Demonstrates one techinque for calibrating sensor input.  The
 sensor readings during the first five seconds of the sketch
 execution define the minimum and maximum of expected values
 attached to the sensor pin.

 The sensor minumum and maximum initial values may seem backwards.
 Initially, you set the minimum high and listen for anything 
 lower, saving it as the new minumum. Likewise, you set the
 maximum low and listen for anything higher as the new maximum.

 The circuit:
 * Analog sensor (potentiometer will do) attached to analog input 0
 * LED attached from digital pin 9 to ground

 created 29 Oct 2008
 By David A Mellis
 Modified 17 Jun 2009
 By Tom Igoe

 http://arduino.cc/en/Tutorial/Calibration

 */

// These constants won't change: const int sensorPin = 2; // pin that the sensor is attached to const int ledPin = 9; // pin that the LED is attached to

const int sensorMin = 1023; // minimum sensor value const int sensorMax = 0; // maximum sensor value

// variables: int sensorValue = 0; // the sensor value

  // turn on LED to signal the start of the calibration period:

    sensorValue = analogRead(sensorPin);

    if (sensorValue > sensorMax) {
      sensorMax = sensorValue;

    if (sensorValue < sensorMin) {
      sensorMin = sensorValue;

  // read the sensor:
  sensorValue = analogRead(sensorPin);

  sensorValue = map(sensorValue, sensorMin, sensorMax, 0, 255);

  sensorValue = constrain(sensorValue, 0, 255);

  // fade the LED using the calibrated value:
  analogWrite(ledPin, sensorValue);

Examples > Analog I/O

Examples > Analog

Calibration

Demonstrates one techinque for calibrating sensor input. The sensor readings during the first five seconds of the sketch execution define the minimum and maximum of expected values.

Circuit

Analog sensor (e.g. potentiometer, light sensor) on analog input 2. LED on digital pin 9.

Code

int sensorPin = 2;
int ledPin = 9;

int val = 0;
int sensorMin = 1023, sensorMax = 0;

void setup() {
  // signal the start of the calibration period
  pinMode(13, OUTPUT);
  digitalWrite(13, HIGH);

  // calibrate during the first five seconds 
  while (millis() < 5000) {
    val = analogRead(sensorPin);

    // record the maximum sensor value
    if (val > sensorMax) {
      sensorMax = val;
    }

    // record the minimum sensor value
    if (val < sensorMin) {
      sensorMin = val;
    }
  }

  // signal the end of the calibration period
  digitalWrite(13, LOW);
}

void loop() {
  val = analogRead(sensorPin);

  // apply the calibration to the sensor reading
  val = map(val, sensorMin, sensorMax, 0, 255);

  // in case the sensor value is outside the range seen during calibration
  val = constrain(val, 0, 255);

  analogWrite(ledPin, val);
}