analogRead()

Used to perform ADC conversion.

Library Documentation

uint16 analogRead(uint8 pin)

Read an analog value from pin.

This function blocks during ADC conversion, and has 12 bits of resolution. The pin must have its mode set to INPUT_ANALOG.

Parameters:

• pin -

  Pin to read from.

Return:

Converted voltage, in the range 0–4095, (i.e. a 12-bit ADC conversion).

See:

pinMode()

Discussion

Reads the value from the specified analog pin. The Maple boards contain 16-channel, 12-bit analog to digital converters. This means that a converter will map input voltages between 0 and 3.3 volts into integer values between 0 and 4095. However, a number of factors interfere with getting full accuracy and precision. For more information, see ADC.

Before calling analogRead() on a pin, that pin must first be configured for analog input, using pinMode(). You only have to do this once, so it’s usually done in setup().

Parameter Discussion

The pin parameter is the number of the analog input pin to read from. The pins which support analog to digital conversion have AIN listed underneath their number on your board’s silkscreen. These pin numbers are available to your program in the boardADCPins board-specific array. The number of pins which are capable of analog to digital conversion on your board is given by the BOARD_NR_ADC_PINS constant. These values are documented for each board in the Board Hardware Documentation pages.

Note

Pin 3 is not marked AIN on the silkscreen for Maple revisions through Rev 5; however it does work as an analog input pin.

Note

If the analog input pin is not connected to anything, the value returned by analogRead() will fluctuate due to a number of reasons (like the values of the other analog inputs, how close your hand is to the board, etc.) in a “random” way.

Example

int analogPin = 3;     // Potentiometer wiper (middle terminal) connected
                       // to analog pin 3. outside leads to ground and +3.3V.
                       // You may have to change this value if your board
                       // cannot perform ADC conversion on pin 3.

int val = 0;           // variable to store the value read

void setup() {
  pinMode(analogPin, INPUT_ANALOG); // set up pin for analog input
}

void loop() {
  val = analogRead(analogPin);    // read the input pin
  SerialUSB.println(val);         // print the value, for debugging with
                                  // a serial monitor
}

Arduino Compatibility

The Arduino board contains a 6 channel (8 channels on the Mini and Nano, 16 on the Mega), 10-bit analog to digital converter with an input voltage range of 0V–5V. This means that it will map input voltages between 0 and 5 volts (which is larger than Maple’s range of 0V-3.3V) into integer values between 0 and 1023 (which is smaller than the Maple’s range of 0–4095).

This yields a theoretical resolution between readings of: 5 volts / 1024 units or .0049 volts (4.9 mV) per unit on Arduino boards, which is larger, and thus less precise, than Maple’s 0.0008 volts (0.8 mV).

If your program expects Arduino-style 10-bit ADC, you can right shift the value of a Maple readout by 2, like so:

// right shift means that the result will be between 0 and 1023;
// be aware that you're losing a lot of precision if you do this
int adc_reading = analogRead(pin) >> 2;

On the Arduino, the input range and resolution can be changed using the analogReference() function. Because of hardware restrictions, this function is not available on the Maple and Maple RET6 Edition. If your inputs lie in a different voltage range than 0V–3.3V, you’ll need to bring them into that range before using analogRead(). See the ADC reference for more information.

See Also

• ADC tutorial
• (Arduino) Tutorial: Analog Input Pins

License and Attribution

Portions of this page were adapted from the Arduino Reference Documentation, which is released under a Creative Commons Attribution-ShareAlike 3.0 License.