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analogRead()

[Analog I/O]

Description

Reads the value from the specified analog pin. Arduino boards contain a multichannel, 10-bit analog to digital converter. This means that it will map input voltages between 0 and the operating voltage(5V or 3.3V) into integer values between 0 and 1023. On an Arduino UNO, for example, this yields a resolution between readings of: 5 volts / 1024 units or, 0.0049 volts (4.9 mV) per unit. See the table below for the usable pins, operating voltage and maximum resolution for some Arduino boards.

The input range can be changed using analogReference(), while the resolution can be changed (only for Zero, Due and MKR boards) using analogReadResolution().

On ATmega based boards (UNO, Nano, Mini, Mega), it takes about 100 microseconds (0.0001 s) to read an analog input, so the maximum reading rate is about 10,000 times a second.

Board Operating voltage Usable pins Max resolution

Uno

5 Volts

A0 to A5

10 bits

Mini, Nano

5 Volts

A0 to A7

10 bits

Mega, Mega2560, MegaADK

5 Volts

A0 to A14

10 bits

Micro

5 Volts

A0 to A11*

10 bits

Leonardo

5 Volts

A0 to A11*

10 bits

Zero

3.3 Volts

A0 to A5

12 bits**

Due

3.3 Volts

A0 to A11

12 bits**

MKR Family boards

3.3 Volts

A0 to A6

12 bits**

*A0 through A5 are labelled on the board, A6 through A11 are respectively available on pins 4, 6, 8, 9, 10, and 12
**The default analogRead() resolution for these boards is 10 bits, for compatibility. You need to use analogReadResolution() to change it to 12 bits.

Syntax

analogRead(pin)

Parameters

pin: the name of the analog input pin to read from (A0 to A5 on most boards, A0 to A6 on MKR boards, A0 to A7 on the Mini and Nano, A0 to A15 on the Mega).

Returns

The analog reading on the pin. Although it is limited to the resolution of the analog to digital converter (0-1023 for 10 bits or 0-4095 for 12 bits). Data type: int.

Example Code

The code reads the voltage on analogPin and displays it.

int analogPin = A3; // potentiometer wiper (middle terminal) connected to analog pin 3
                    // outside leads to ground and +5V
int val = 0;  // variable to store the value read

void setup() {
  Serial.begin(9600);           //  setup serial
}

void loop() {
  val = analogRead(analogPin);  // read the input pin
  Serial.println(val);          // debug value
}

Notes and Warnings

If the analog input pin is not connected to anything, the value returned by analogRead() will fluctuate based on a number of factors (e.g. the values of the other analog inputs, how close your hand is to the board, etc.).