Input/Output

analogRead() (ADC)

analogRead

// SYNTAX
analogRead(pin);

// EXAMPLE USAGE
int ledPin = D1;                // LED connected to digital pin D1
int analogPin = A0;             // potentiometer connected to analog pin A0
int val = 0;                    // variable to store the read value

void setup()
{
  // Note: analogPin pin does not require pinMode()

  pinMode(ledPin, OUTPUT);      // sets the ledPin as output
}

void loop()
{
  val = analogRead(analogPin);  // read the analogPin
  analogWrite(ledPin, val/16);  // analogRead values go from 0 to 4095, analogWrite values from 0 to 255
  delay(10);
}

Reads the value from the specified analog pin.

analogRead() takes one argument pin: the number of the analog input pin to read from, such as A0 or A1.

analogRead() returns an integer value ranging from 0 to 4095 (12-bit).


Gen 3 Devices (B Series SoM, Tracker SoM, Tracker One, Boron, Argon, and E404X):

The Gen 3 Feather devices (Argon, Boron, Xenon) have 6 channels (A0 to A5) with a 12-bit resolution. This means that it will map input voltages between 0 and 3.3 volts into integer values between 0 and 4095. This yields a resolution between readings of: 3.3 volts / 4096 units or, 0.0008 volts (0.8 mV) per unit.

The sample time to read one analog value is 10 microseconds.

The Boron SoM has 8 channels, A0 to A7.

The Tracker SoM has 8 channels, A0 to A7, however these pins are the same physical pins D0 to D7.

The Tracker One only exposes one analog input, A3, on the external M8 connector. Pin A0 is connected to the NTC thermistor on the carrier board.


P2 and Photon 2 Devices:

The P2 and Photon 2 have four dedicated ADC pins, and two shared pins. If you are not using pins D0 and D1 for I2C or digital GPIO, you can use these pins are ADC inputs by using analogRead(A3) and analogRead(A4).

Pin Pin Name Description Interface MCU
23 A5 / D14 A5 Analog in, GPIO, PWM. ADC_0 PB[4]
35 D1 / A4 D1 GPIO, PWM, I2C SCL, A4 Analog In ADC_1 PB[5]
36 D0 / A3 D0 GPIO, PWM, I2C SDA, A3 Analog In ADC_2 PB[6]
43 A1 / D12 A1 Analog in, GPIO ADC_5 PB[2]
49 A2 / D13 A2 Analog in, PWM, GPIO ADC_3 PB[7]
50 A0 / D11 A0 Analog in, GPIO ADC_4 PB[1]
  • ADC inputs are single-ended and limited to 0 to 3.3V
  • Resolution is 12 bits


Gen 2 Devices (E Series, Electron, Photon, and P2; does not include E404X):

The device has 8 channels (A0 to A7) with a 12-bit resolution. This means that it will map input voltages between 0 and 3.3 volts into integer values between 0 and 4095. This yields a resolution between readings of: 3.3 volts / 4096 units or, 0.0008 volts (0.8 mV) per unit.

Before 0.5.3 Note: do not set the pinMode() with analogRead(). The pinMode() is automatically set to AN_INPUT the first time analogRead() is called for a particular analog pin. If you explicitly set a pin to INPUT or OUTPUT after that first use of analogRead(), it will not attempt to switch it back to AN_INPUT the next time you call analogRead() for the same analog pin. This will create incorrect analog readings.

Since 0.5.3 Note: you do not need to set the pinMode() with analogRead(). The pinMode() is automatically set to AN_INPUT any time analogRead() is called for a particular analog pin, if that pin is set to a pinMode other than AN_INPUT. If you explicitly set a pin to INPUT, INPUT_PULLUP, INPUT_PULLDOWN or OUTPUT before using analogRead(), it will switch it back to AN_INPUT before taking the reading. If you use digitalRead() afterwards, it will automatically switch the pinMode back to whatever you originally explicitly set it to.