Arduino - AnalogWrite

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analogWrite()

Description

Writes an analog value (PWM wave) to a pin. Can be used to light a LED at varying brightnesses or drive a motor at various speeds. After a call to analogWrite(), the pin will generate a steady square wave of the specified duty cycle until the next call to analogWrite() (or a call to digitalRead() or digitalWrite() on the same pin). The frequency of the PWM signal is approximately 490 Hz.

On newer Arduino boards (including the Mini and BT) with the ATmega168 chip, this function works on pins 3, 5, 6, 9, 10, and 11. Older USB and serial Arduino boards with an ATmega8 only support analogWrite() on pins 9, 10, and 11.

Syntax

analogWrite(pin, value)

Parameters

pin: the pin to write to.

value: the duty cycle: between 0 (always off) and 255 (always on).

Returns

nothing

Notes and Known Issues

analogWrite has nothing whatsoever to do with the analog pins or analogRead.

You do not need to call pinMode() to set the pin as an output before calling analogWrite().

The PWM outputs generated on pins 5 and 6 will have higher-than-expected duty cycles. This is because of interactions with the millis() and delay() functions, which share the same internal timer used to generate those PWM outputs. This will be noticed mostly on low duty-cycle settings (e.g 0 - 10) and may result in analogWrite(x, 0) not fully turning off the output on pins 5 & 6, as one would expect.

Example

Sets the output to the LED proportional to the value read from the potentiometer.

 
int ledPin = 9;      // LED connected to digital pin 9
int analogPin = 3;   // potentiometer connected to analog pin 3
int val = 0;         // variable to store the read value

void setup()
{
  pinMode(ledPin, OUTPUT);   // sets the pin as output
}

void loop()
{
  val = analogRead(analogPin);   // read the input pin
  analogWrite(ledPin, val / 4);  // analogRead values go from 0 to 1023, analogWrite values from 0 to 255
}