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Reference > Language > Functions > Analog io > Analogwrite

analogWrite()

[Analog I/O]

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 rectangular wave of the specified duty cycle until the next call to analogWrite() (or a call to digitalRead() or digitalWrite()) on the same pin.

Board PWM Pins * PWM Frequency

UNO (R3 and earlier), Nano, Mini

3, 5, 6, 9, 10, 11

490 Hz (pins 5 and 6: 980 Hz)

UNO R4 (Minima, WiFi) *

3, 5, 6, 9, 10, 11

490 Hz

Mega

2 - 13, 44 - 46

490 Hz (pins 4 and 13: 980 Hz)

GIGA R1 **

2 - 13

500 Hz

Leonardo, Micro, Yún

3, 5, 6, 9, 10, 11, 13

490 Hz (pins 3 and 11: 980 Hz)

UNO WiFi Rev2, Nano Every

3, 5, 6, 9, 10

976 Hz

MKR boards *

0 - 8, 10, A3, A4

732 Hz

MKR1000 WiFi **

0 - 8, 10, 11, A3, A4

732 Hz

Zero **

3 - 13, A0, A1

732 Hz

Nano 33 IoT **

2, 3, 5, 6, 9 - 12, A2, A3, A5

732 Hz

Nano 33 BLE/BLE Sense ****

1 - 13, A0 - A7

500 Hz

Due ***

2-13

1000 Hz

101

3, 5, 6, 9

pins 3 and 9: 490 Hz, pins 5 and 6: 980 Hz

* These pins are officially supported PWM pins. While some boards have additional pins capable of PWM, using them is recommended only for advanced users that can account for timer availability and potential conflicts with other uses of those pins.
** In addition to PWM capabilities on the pins noted above, the MKR, Nano 33 IoT, Zero and UNO R4 boards have true analog output when using analogWrite() on the DAC0 (A0) pin.
*** In addition to PWM capabilities on the pins noted above, the Due and GIGA R1 boards have true analog output when using analogWrite() on pins DAC0 and DAC1.
**** Only 4 different pins can be used at the same time. Enabling PWM on more than 4 pins will abort the running sketch and require resetting the board to upload a new sketch again.

You do not need to call pinMode() to set the pin as an output before calling analogWrite().
The analogWrite function has nothing to do with the analog pins or the analogRead function.

Syntax

analogWrite(pin, value)

Parameters

pin: the Arduino pin to write to. Allowed data types: int.
value: the duty cycle: between 0 (always off) and 255 (always on). Allowed data types: int.

Returns

Nothing

Example Code

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
}

Notes and Warnings

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 a value of 0 not fully turning off the output on pins 5 and 6.

See also

  • DEFINITION PWM