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.. highlight:: cpp
.. _lang-analogread:
.. _lang-api-analogread:
analogRead()
============
Used to perform ADC conversion.
.. contents:: Contents
:local:
Library Documentation
---------------------
.. doxygenfunction:: analogRead
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 :ref:`adc`.
Before calling analogRead() on a pin, that pin must first be
configured for analog input, using :ref:`lang-pinMode`. You only have
to do this once, so it's usually done in :ref:`lang-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 :ref:`boardADCPins
<lang-board-values-adc-pins>` 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 :ref:`Board Hardware Documentation
<index-boards>` 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 :ref:`right
shift <lang-bitshift>` 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;
.. FIXME [0.1.0] Mention that Native can do analogReference()
On the Arduino, the input range and resolution can be changed using
the `analogReference()
<http://arduino.cc/en/Reference/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 :ref:`ADC reference <adc-range>` for
more information.
See Also
--------
- :ref:`ADC tutorial <adc>`
- `(Arduino) Tutorial: Analog Input Pins <http://arduino.cc/en/Tutorial/AnalogInputPins>`_
.. include:: /arduino-cc-attribution.txt
|
