This node.js module supports querying air temperature and relative humidity from a compatible DHT sensor.

$ npm install node-dht-sensor

This module uses the BCM2835 library that requires access to /open/mem. Because of this, you will typically run node with admin privileges.

The first step is initializing the sensor by specifying the sensor type and which GPIO pin the sensor is connected. It should work for DHT11, DHT22 and AM2302 sensors. If the initialization succeeds when you can call the read function to obtain the latest readout from the sensor. Readout values contains a temperature and a humidity property.

This sample queries the AM2302 sensor connected to the GPIO 4 every 2 seconds and displays the result on the console.

var sensorLib = require('node-dht-sensor');

var sensor = {
    initialize: function () {
        return sensorLib.initialize(22, 4);
    },
    read: function () {
        var readout = sensorLib.read();
        console.log('Temperature: ' + readout.temperature.toFixed(2) + 'C, ' +
            'humidity: ' + readout.humidity.toFixed(2) + '%');
        setTimeout(function () {
            sensor.read();
        }, 2000);
    }
};

if (sensor.initialize()) {
    sensor.read();
} else {
    console.warn('Failed to initialize sensor');
}

The following example shows a method for querying multiple sensors connected to the same Raspberry Pi. For this example, we have two sensors:

1. A DHT11 sensor connected to GPIO 17
2. High-resolution DHT22 sensor connected to GPIO 4

var sensorLib = require("node-dht-sensor");

var sensor = {
    sensors: [ {
        name: "Indoor",
        type: 11,
        pin: 17
    }, {
        name: "Outdoor",
        type: 22,
        pin: 4
    } ],
    read: function() {
        for (var a in this.sensors) {
            var b = sensorLib.readSpec(this.sensors[a].type, this.sensors[a].pin);
            console.log(this.sensors[a].name + ": " + 
              b.temperature.toFixed(1) + "C, " + 
              b.humidity.toFixed(1) + "%");
        }
        setTimeout(function() {
            sensor.read();
        }, 2000);
    }
};

sensor.read();

Standard node-gyp commands are used to build the module.

1. Generate the configuration files

$ node-gyp configure

2. Build the component

$ node-gyp build

Verbose output from the module can be enabled by defining VERBOSE during the module compilation. For example, this can be enabled via the binging,gyp file:

{
  'targets': [
    {
      'target_name': 'node-dht-sensor',
      'sources': [ 'node-dht-sensor.cpp' ],
      'libraries': [ '-lbcm2835' ],
      'defines': [ 'VERBOSE']
    }
  ]
}

There are many ways you can get Node.js installed on your Raspberry Pi but the following method is very convenient for getting started on the latest version, very quickly.

$ wget http://node-arm.herokuapp.com/node_latest_armhf.deb 
$ sudo dpkg -i node_latest_armhf.deb

[1]: Node.js latest release - http://nodejs.org/dist/latest/

[2]: BCM2835 - http://www.airspayce.com/mikem/bcm2835/

[3]: Node.js native addon build tool - https://github.com/TooTallNate/node-gyp