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node-dht-sensor

node-dht-sensor

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

Installation

$ npm install node-dht-sensor

Usage

This module depends on the BCM2835 library that must be installed on your board before you can actually use this module.

To initialize the sensor, you have to specify the sensor type and the GPIO pin where the sensor is connected to. It should work for DHT11, DHT22 and AM2302 sensors.

You should use sensorType value to match the sensor as follows:

Sensor sensorType value
DHT11 11
DHT22 or AM2302 22

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.

First Example

example1

This sample queries a DHT22 sensor connected to the GPIO 4 and prints out the result on the console.

var sensor = require('node-dht-sensor');
 
sensor.read(22, 4, function(err, temperature, humidity) {
    if (!err) {
        console.log('temp: ' + temperature.toFixed(1) + '°C, ' +
            'humidity: ' + humidity.toFixed(1) + '%'
        );
    }
});

Multiple Sensors Example

example2

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.read(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();

Reference for building from source

Standard node-gyp commands are used to build the module. So, just make sure you have node and node-gyp as well as the Broadcom library to build the project.

  1. Download BCM2835 library and follow installation instructions.

  2. In case, you don't have node-gyp, install it first:

    $ sudo npm install node-gyp -g
  3. Generate the configuration files

    $ node-gyp configure
  4. Build the component

    $ node-gyp build

Tracing and Debugging

Verbose output from the module can be enabled by by specifying the --dht_verbose=true flag when installing the node via npm.

$ npm install node-dht-sensor --dht_verbose=true

if you are interested in enabling trace when building directly from source you can enable the -Ddht_verbose flag when running node-gyp configure.

$ node-gyp configure -- -Ddht_verbose=true

Appendix A: Quick Node.js installation guide

There are many ways you can get Node.js installed on your Raspberry Pi. Here is just one of way you can do it.

$ wget http://nodejs.org/dist/v7.1.0/node-v7.1.0-linux-armv7l.tar.xz
$ tar xvfJ node-v7.1.0-linux-armv7l.tar.xz
$ sudo mv node-v7.1.0-linux-armv7l /opt
$ sudo update-alternatives --install "/usr/bin/node" "node" "/opt/node-v7.1.0-linux-armv7l/bin/node" 1
$ sudo update-alternatives --set node /opt/node-v7.1.0-linux-armv7l/bin/node
$ sudo update-alternatives --install "/usr/bin/npm" "npm" "/opt/node-v7.1.0-linux-armv7l/bin/npm" 1

Please note that you may have to use armv6l instead of arm7l if you have an early Raspberry Pi model.

References

[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

[4]: GPIO: Raspbery Pi Models A and B - https://www.raspberrypi.org/documentation/usage/gpio/