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AIO API

The AIO API supports reading analog input pins that measure the analog voltage signal between 0 and a maximum voltage (usually 3.3 or 5 Volts), then do Analog-to-Digital Conversion (ADC) with a resolution of 10 or 12 bits on most boards, so that the result (pin value) is 0 to 1023 or 0 to 4095, inclusively.

On some boards access to AIO may be asynchronous. This API uses synchronous methods.

The AIO API object

AIO functionality is exposed by an object that can be obtained by using the aio() method of the Board API. See also the Web IDL. The API object exposes the following method:

Method Description
open() synchronous open

The AIO open(options) method

Configures an AIO pin using data provided by the options argument. It involves the following steps:

  • If options is a string, create a dictionary 'init' and use the value of options to initialize the init.pin property.
  • Otherwise if options is a number, create a dictionary 'init' and use the value of options to initialize the init.pin property.
  • Otherwise if options is a dictionary, let init be options. It may contain the following AIO properties, where at least pin MUST be specified:
    • pin for board pin name with the valid values defined by the board, or for the numeric index of the analog pin;
    • precision for the bit width of a sample (if the board supports setting the sampling rate).
  • If any property of init is specified and has an invalid value on the given board, as defined by the board documentation, throw TypeError.
  • Request the underlying platform to initialize AIO on init.pin (if defined) or otherwise init.channel.
  • In case of failure, throw InvalidAccessError.
  • Let aio be the AIOPin](#aiopin) object that represents the hardware pin identified by init.pin, as defined by the board documentation.
  • If init.precision is defined, request the board to set the precision and initialize the aio.precision property with the value supported by the board. If there is an error, throw InvalidAccessError.
  • Initialize the aio.value property with undefined.
  • Return the aio object.

The AIO interface

The AIO object extends the Pin object.

Property Type Optional Default value Represents
pin String or Number no undefined board name for the pin
precision unsigned long yes undefined bit length of digital sample
Method Description
read() synchronous read
close() close the pin

The pin property inherited from Pin can take values defined by the board documentation, usually strings prefixed by "A", but it can also be specified as the numeric index of the analog pin, where pin 0 corresponding to the first analog pin and so forth.

The precision property represents the bit length of the digital sample. It is usually 10 or 12 bits, depending on board.

The unsigned long read() method

Performs a synchronous read operation for the pin value. It returns the pin value representing the last sampling.

The close() method

Called when the application is no longer interested in the pin. Until the next open() is called, invoking the read() method throws InvalidAccessError.

Examples

try {
  var aio = require("board").aio();  // initialize AIO on the board

  var a1 = aio.open("A1");
  console.log(board.name + " AIO pin 1 value: " + a1.read());
  a1.close();

  var a4 = aio.open({pin: "A4", precision: 12 });

  setTimeout(function() {
    a4.close();
  }, 10500);

  setInterval(function() {
    console.log("AIO pin 4 value: " + a4.read());
  }, 1000);
} catch (err) {
  console.log("AIO error: " + err.message);
};