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-.. highlight:: cpp
-
-.. _arduino-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 board
-contains a 16-channel, 12-bit analog to digital converter. 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 3.3V / 4096 units, or 0.8 millivolts. 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:`arduino-pinMode` (you only
-have to do this once, so it's usually done in :ref:`arduino-setup`\ ).
-
-It takes about 0.8 microseconds (.0000008 seconds) to read an analog
-input, so the maximum sample rate using this function is approximately
-1.3 million samples per second\ [#fsamp]_.
-
-
-Parameter Discussion
---------------------
-
-The pin parameter is the number of the analog input pin to read from.
-Header pins on the Maple with ADC functionality (marked as "AIN" on
-the silkscreen) are:
-
- 0, 1, 2, 3, 10, 11, 12, 13, 15, 16, 17, 18, 19, 20, 27, 28
-
-Note that pins 3, 27, and 28 are not marked AIN on the silkscreen
-for Maple revisions through Rev 5, however, they **do work** as
-analog input pins.
-
-Note
-----
-
-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.) in a seemingly random way.
-
-
-Example
--------
-
- ::
-
-
- int analogPin = 3; // potentiometer wiper (middle terminal) connected
- // to analog pin 3. outside leads to ground and +3.3V
- int val = 0; // variable to store the value read
-
- void setup() {
- pinMode(analogPin, INPUT_ANALOG); // set up pin for analog input
- SerialUSB.begin(); // set up usb virtual COM port
- }
-
- 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 <arduino-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;
-
-On the Arduino, the input range and resolution can be changed using
-their implementation of `analogReference()
-<http://arduino.cc/en/Reference/AnalogReference>`_\ . Because of the
-way its hardware (as of Rev 5) was designed, it's not possible to
-implement analogReference on the Maple, so this function doesn't
-exist. 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.
-Some basic tools to accomplish this are `resistor dividers
-<http://en.wikipedia.org/wiki/Voltage_divider>`_ and `Zener diodes
-<http://en.wikipedia.org/wiki/Voltage_source#Zener_voltage_source>`_\
-. However, opamps and other powered components can also be used if
-greater precision is required.
-
-Finally, On the Arduino, it takes significantly longer to read analog
-input: about 100 microseconds (0.0001 s), so the maximum reading rate
-is 10,000 times a second.
-
-
-See also
---------
-
-- :ref:`ADC note <adc>`
-- `(Arduino) Tutorial: Analog Input Pins <http://arduino.cc/en/Tutorial/AnalogInputPins>`_
-
-
-.. rubric:: Footnotes
-
-.. [#fsamp] This is based on the current configuration of a 55.5 cycle
- sample time, at 72 MHz. However, the minimum sample time *possible*
- is 1.5 cycles, leading to a theoretical maximum of approximately 48
- million samples per second (of course, doing anything with the
- readings also consumes cycles, so this maximum can't be reached in
- practice).
-
- See the `STM32 Reference Manual <full-manual>`_, ยงยง11.12.4--5
- (pp. 225--226), for more information on the low-level bit twiddling
- currently necessary to change the sample time. For examples of how
- the ADCs are configured in libmaple, see `adc.h
- <http://github.com/leaflabs/libmaple/blob/master/libmaple/adc.h>`_
- and `adc.c
- <http://github.com/leaflabs/libmaple/blob/master/libmaple/adc.c>`_\
- . Be aware that changing the sample time has important
- consequences related to the impedance of the device connected to
- the input pin. If you want to make changes, as a minimum, you
- should first read ST's application notes on `ADC modes
- <stm32-adc-modes>`_ and `ADC oversampling
- <stm32-adc-oversampling>`_.
-
-
-.. include:: cc-attribution.txt \ No newline at end of file