node-dht-sensor

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


Installation

``shell session
$ npm install node-dht-sensor
`

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

`shell session
$ 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.

$3

!example1

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

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

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

$3

!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

`javascript
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();
`

$3

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.

`javascript
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:

`javascript
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();
`

$3

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%.

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

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

`javascript
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.

`shell session
$ 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.

$3

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:

`shell session
$ 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

`shell session
$ node-gyp configure
`

3. Build the component
`shell session
$ node-gyp build
`

$3

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

`shell session
$ 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.

`shell session
$ node-gyp configure -- -Ddht_verbose=true
`

$3

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

`shell session
$ 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.

$3

[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/