aio.md

ZJS API for Analog I/O (AIO)

• Introduction
• Web IDL
• API Documentation
• Sample Apps

Introduction

The AIO API supports analog I/O pins. So far, the support is just for analog-to-digital conversion (ADC). This measures an analog voltage input on a pin and converts it into a digital representation. The values are dependent on the resolution and limits of the particular device. For example, the Arduino 101 has 12-bit resolution and uses 3.3V on its six analog input pins. So for a voltage between 0 - 3.3V it returns a digital value of 0 - 4095.

Other Arduino devices typically have 10-bit resolution and some may use 5V as the upper limit instead.

Hardware may have other analog features such as comparators but so far, we do not have support for this.

Web IDL

This IDL provides an overview of the interface; see below for documentation of specific API functions.

// require returns an AIO object
// var aio = require('aio');

[NoInterfaceObject]
interface AIO {
    AIOPin open(AIOInit init);
};

dictionary AIOInit {
    unsigned long pin;
};

[NoInterfaceObject]
interface AIOPin {
    unsigned long read();
    void readAsync(ReadCallback callback);  // TODO: change to return a promise
    void on(string eventType, ReadCallback callback);
    void close();
};

callback ReadCallback = void (unsigned long value);

API Documentation

AIO.open

AIOPin open(AIOInit init);

The init object lets you set the pin number. You can either use a raw number for your device or use the board support module such as Arduino 101 or K64F to specify a named pin.

Use the AIOPin object returned to read values from the pin.

AIOPin.read

unsigned long read();

Returns the latest reading from the pin. Blocks until it gets the result.

AIOPin.readAsync

void readAsync(ReadCallback callback);

Pass a function for callback that will be called later when the result is obtained.

WARNING: Making an async call like this allocates some memory while the call is pending, so if you issue them faster than they are fulfilled, you will eventually run out of memory - pretty soon on these small devices. So the best practice would be to make sure you only have a small, fixed number pending at any given time.

NOTE: This function will probably be replaced with a version that instead returns a promise.

AIOPin.on

void on(string eventType, ReadCallback callback);

Currently, the only supported eventType is 'change', and callback should be either a function or null. When a function is passed for the change event, the function will be called any time the analog voltage changes. (At the moment, it actually gets called periodically even when it hasn't changed.) When null is passed for the change event, the previously registered callback will be discarded and no longer called.

AIOPin.close

void close();

Closes the AIOPin. Once it is closed, all event handlers registered will no longer be called.

Sample Apps

• AIO sample
• Arduino Read Analog Voltage sample
• Arduino Analog Read Serial sample
• WebBluetooth Demo