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Analog Input

A potentiometer is a simple knob that provides a variable resistance, which we can read into the Arduino board as an analog value. In this example, that value controls the rate at which an LED blinks.

We connect three wires to the Arduino board. The first goes to ground from one of the outer pins of the potentiometer. The second goes from 5 volts to the other outer pin of the potentiometer. The third goes from analog input 2 to the middle pin of the potentiometer.

By turning the shaft of the potentiometer, we change the amount of resistence on either side of the wiper which is connected to the center pin of the potentiometer. This changes the relative "closeness" of that pin to 5 volts and ground, giving us a different analog input. When the shaft is turned all the way in one direction, there are 0 volts going to the pin, and we read 0. When the shaft is turned all the way in the other direction, there are 5 volts going to the pin and we read 1023. In between, analogRead() returns a number between 0 and 1023 that is proportional to the amount of voltage being applied to the pin.

Circuit

An analog input connected to analog input pin 0.

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Schematic

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Code

 /*
   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 16 Jun 2009
  By Tom Igoe
  
  http://arduino.cc/en/Tutorial/AnalogInput
  
  */


 int sensorPin = 0;    // 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:
   delay(sensorValue);          
   // turn the ledPin off:        
   digitalWrite(ledPin, LOW);   
   // stop the program for for <sensorValue> milliseconds:
   delay(sensorValue);                  
 }