node-dht-sensor

A simple node.js module for reading temperature and relative humidity using a compatible DHT sensor.

Installation

$ npm install node-dht-sensor

For use with the Raspberry Pi 5, creating dependency on libgpiod, installation is as follows:

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

The above accounts for the architectural changes in the Raspberry Pi 5 which are incompatible with the BCM2835 library.

Usage

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

This sample queries a DHT11 sensor connected to the GPIO 4 and prints out the result on the console.

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

sensor.read(11, 4, function(err, temperature, humidity) {
  if (!err) {
    console.log(`temp: ${temperature}°C, humidity: ${humidity}%`);
  }
});

Multiple Sensors Example

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

app.read();

Promises API

Promises API provides an alternative read method that returns a Promise object rather than using a callback. The API is accessible via require('node-dht-sensor').promises.

var sensor = require("node-dht-sensor").promises;

// You can use `initialize` and `setMaxTries` just like before
sensor.setMaxRetries(10);
sensor.initialize(22, 17);

// You can still use the synchronous version of `read`:
// var readout = sensor.readSync(22, 4);

sensor.read(22, 17).then(
  function(res) {
    console.log(
      `temp: ${res.temperature.toFixed(1)}°C, ` +
        `humidity: ${res.humidity.toFixed(1)}%`
    );
  },
  function(err) {
    console.error("Failed to read sensor data:", err);
  }
);

Using async/await:

const sensor = require("node-dht-sensor").promises;

async function exec() {
  try {
    const res = await sensor.read(22, 4);
    console.log(
      `temp: ${res.temperature.toFixed(1)}°C, ` +
        `humidity: ${res.humidity.toFixed(1)}%`
    );
  } catch (err) {
    console.error("Failed to read sensor data:", err);
  }
}

exec();

Test mode

A test mode of operation is available since version 0.2.0. In this mode of operation, the library does not communicate with the sensor hardware via the GPIO but instead it returns a pre-configured readout value. You can use the test mode during development without the need to have an actual sensor connected.

To enable the test mode, fake values must be defined at initialization. In the example below we specify fixed values for temperature equal to 21°C and humidity equal to 60%.

sensor.initialize({
  test: {
    fake: {
      temperature: 21,
      humidity: 60
    }
  }
});

After initialization, we can call the read method as usual.

sensor.read(22, 4, function(err, temperature, humidity) {
  if (!err) {
    console.log(
      `temp: ${temperature.toFixed(1)}°C, ` +
        `humidity: ${humidity.toFixed(1)}%`
    );
  }
});

And the result will always be the configured readout value defined at initialization.

$ node examples/fake-test.js
temp: 21.0°C, humidity: 60.0%
$ node examples/fake-test.js
temp: 21.0°C, humidity: 60.0%

You can find a complete source code example in examples/fake-test.js.

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

   $ sudo npm install -g node-gyp
   $ sudo update-alternatives --install /usr/bin/node-gyp node-gyp /opt/node-v10.15.3-linux-armv7l/bin/node-gyp 1

2. Generate the configuration files

   $ node-gyp configure

3. 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 https://nodejs.org/dist/v14.15.4/node-v14.15.4-linux-armv7l.tar.xz
$ tar xvfJ node-v14.15.4-linux-armv7l.tar.xz
$ sudo mv node-v14.15.4-linux-armv7l /opt
$ sudo update-alternatives --install /usr/bin/node node /opt/node-v14.15.4-linux-armv7l/bin/node 1
$ sudo update-alternatives --set node /opt/node-v14.15.4-linux-armv7l/bin/node
$ sudo update-alternatives --install /usr/bin/npm npm /opt/node-v14.15.4-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 download - https://nodejs.org/en/download/

[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/