Building IoT Applications

Any application built on the Appivo-platform can have IoT-functionality – meaning you can have devices connected to your application that contribute functionality. Examples of this could be a device monitoring the temperature of a room, controlling a doorlock or displaying information on a TV. An application may even have several kinds of devices connected to it and these different device may need to run different code. That’s why an appivo-application can have several deviceprofiles. A deviceprofile is the collection of code required for a certain type of device when being connected to your application.

The deviceprofile contains a set of event-handlers as the programming model for a device is strictly event-based. The platform emits a few fundamental events – such as App.Start and App.Stop – as you might guess these events are emitted when the application starts and stops, on the device that is. Typically you will initialize datastructures and features when the app starts and then clean everything up when it stops.

Devices can also have timers that emit “tick”-events according to a schedule that you determine, this way you can for instance collect data from a sensor at a regular interval. The device may also “listen” for messages being received on messaging-topics – this allows the device to interact with the part of your application running in the cloud, as well as other devices of course.

Devices may also make use of various plugins, there are plugins for interfacing with hardware components  such as I²C, SPI and GPIO – but that’s not all, there is also a plugin for controlling an embedded chrome-browser which can be used to open up web-based user-interfaces that are also part of your application. This makes it very easy to build a digital signage system that can be used with a regular TV.

The DeviceContext API

The DeviceContext is the main interface when interacting with the device. Through it you can get access to hardware-features and general functionality. Notice that when interacting with the database this API is asynchronous and related methods return a Promise. This section of the document provides a description of the DeviceContext API:

Examples

1. Creating a record and storing it in the database.

var sensorData = 7;
var appliance = context.getAppliance();
var record = context.createRecord("SensorValue", {
   "appliance_id": appliance.id,
   "Value": sensorData
});
context.create(record);

2. Getting a record from the database

context.get("Sensor", sensorId).then(function(record) {
   context.log("Got record from database " + record.id);
});

3. Executing a query

context.query("#MyQuery", {
   "threshold": 100
}).then(function(records) {
   for (var i = 0; i < records.length; i++) {
      var record = records[i];
      context.log("Got record " + i + " with id " + record.id);
   }
});

4. Publish a message

context.publish("#mytopic", {
   value: 10,
   status: "OPEN"
});

5. Storing data locally

var counter = compute();
context.setData("counter", counter, "APP");

And retrieving it at a later time:

var counter = context.getData("counter");

The GPIO Module

Examples

//Make GPIO pin 0 blink 
context.getModule("gpio").getPin("GPIO 0").blink(500);

The I2C Module

Examples

// Get the i2c module
var i2c = context.getModule("i2c");

// Get the device on bus 1, address 0x29
var device = i2c.getDevice(1, 0x29);

// Write 0x30 to the internal register address 0x8A
device.write(0x8A, 0x30);

The SPI Module

Examples

// Get the SPI-module
var spi = context.getModule("spi");

// Get the device on CS 0
var device = spi.getDevice(0, 0);

//Write 0x0A, 0x0B, 0xC to the device using CS 0 and store the result (2 bytes)
var bytes = device.write([0x0A, 0x0B, 0x0C]);

//assemble the 2 bytes into a single 16-bit unsigned integer (assuming big endian byte order)
var uInt16 = bytes[0] << 8 | bytes[1];