.. 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 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:`lang-pinMode` (you only have to do this once, so it's usually done in :ref:`lang-setup`\ ). Parameter Discussion -------------------- .. FIXME generalize Maple-specific information 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 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 ` 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 Mention Native can do analogReference(), when it's time On the Arduino, the input range and resolution can be changed using their implementation of `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 `_ and `Zener diodes `_\ . However, `operational amplifiers `_ and other powered components can also be used if greater precision is required. See also -------- - :ref:`ADC tutorial ` - `(Arduino) Tutorial: Analog Input Pins `_ .. include:: cc-attribution.txt