Sensors

Sensors and other devices are presented as services that can be searched for based on various properties. In the following sample, we look for an ambient light (luminance) and a temperature sensor. The code that looks for sensors is implemented as a module and can be imported using the familiar require() function.

var sensors = {};

var ambientLightRefs = serviceRegistry.find('io.macchina.physicalQuantity == "luminance"');
if (ambientLightRefs.length > 0)
{
    sensors.ambientLight = ambientLightRefs[0].instance();
    logger.information('Ambient Light: ' + sensors.ambientLight.getPropertyString('name'));
}

var temperatureRefs = serviceRegistry.find('io.macchina.physicalQuantity == "temperature"');
if (temperatureRefs.length > 0)
{
    sensors.temperature = temperatureRefs[0].instance();
    logger.information('Temperature: ' + sensors.temperature.getPropertyString('name'));
}

module.exports = sensors;
						

Database

Once we have a sensor object, we can get a callback whenever the measured value changes. In the following example, we write the current sensor value into a SQLite database, together with a timestamp.

var sensors = require("sensors.js");

var dbPath = application.config.getString('datalogger.database');
var dbSession = new DBSession('SQLite', dbPath);

sensors.temperature.on('valueChanged', 
    function (event) 
    {
        dbSession.execute('INSERT INTO datalog VALUES (?, ?)',
            Date(),
            event.data);
    });
						

Serial Port

Many devices provide a serial (UART) interface and support a simple text-based protocol. It's easy to process data received from such devices.

var serial = null;
var serialRef = serviceRegistry.findByName('io.macchina.serialport#0');
if (serialRef)
{
    serial = serialRef.instance();
    logger.notice("SerialDevice found: " + serial.getPropertyString("device"));
}

serial.setFeature("events", true);
serial.setPropertyString("delimiters", "\n");
serial.setPropertyDouble("timeout", 0.1);
serial.on("lineReceived", 
    function(line) 
    { 
        logger.notice("Received: " + line.data); 
    });
						

Cloud Services

The following example shows how to send data to a cloud service providing a REST interface. We periodically obtain temperature and ambient light measurements and send them to the AirVantage M2M Cloud service.

var sensors = require('sensors.js');

var username = application.config.getString("airvantage.username");
var password = application.config.getString("airvantage.password");

setInterval(
    function()
    {
        var httpRequest = new HTTPRequest('POST', 'https://na.airvantage.net/device/messages');
        var epoch = 1000*DateTime().epoch; // seconds to milliseconds
        httpRequest.timeout = 10.0;
        httpRequest.authenticate(username, password);
        httpRequest.content = JSON.stringify(
            [
                {
                    "sensor.temperature": 
                        [
                            {
                                "timestamp": epoch,
                                "value": sensors.temperature.value()
                            }
                        ],
                    "sensor.ambientLight":
                        [ 
                            {
                                "timestamp": epoch,
                                "value": sensors.ambientLight.value()
                            }
                        ]
                }
            ]
        );
        var httpResponse = httpRequest.send();
        if (httpResponse.status != 200)
        {
            logger.error("Failed sending data to AirVantage: " + httpResponse.reason);
        }
    },
    30000);
						

The above sample blocks in send() until the HTTP request has been completed. HTTP requests can also be sent asynchronously. In this case, a callback function will be called when the request has completed.

        // ...
        httpRequest.send(
            function (result)
            {
                if (result.error)
                {
                    logger.error(result.error);
                }
                else if (result.response.status != 200)
                {
                    logger.error("HTTP request failed: " + result.response.reason);
                }
            });
        // ...
						

JavaScript Servlets

The following example shows how to implement a servlet in JavaScript that reads sensor data from the SQLite database and formats it as JSON.

var dbPath = application.config.getString('logger.database');
var dbSession = new DBSession('SQLite', dbPath);
dbSession.pageSize = 20;

var recordSet = dbSession.execute('SELECT timestamp, temperature FROM datalog ORDER BY timestamp DESC');
response.contentType = 'application/json';
response.write(recordSet.toJSON());
response.send();