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Demonstrates one technique 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 minimum and maximum initial values may seem backwards.
Initially, you set the minimum high and listen for anything
lower, saving it as the new minimum. 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 30 Aug 2011
By Tom Igoe
This example code is in the public domain.
// These constants won't change:
const int sensorPin = A0; // 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);