signalk-raspberry-pi-sht31/index.js

SignalK node server plugin that reads data from SHT31 temperature/humidity sensors on Raspberry-Pi

/*
 * Copyright 2025 John Blackwood
 *
 * Add the MIT license
 */

const { SHT31 } = require('sht31-sensor')

module.exports = function (app) {
  let timer = null
  let plugin = {}

  plugin.id = 'signalk-raspberry-pi-sht31'
  plugin.name = 'Raspberry-Pi SHT31'
  plugin.description = 'SHT31 temperature/humidity sensors on Raspberry-Pi'

  plugin.schema = {
    type: 'object',
    properties: {
      rate: {
        title: "Sample Rate (in seconds)",
        type: 'number',
        default: 60
      },
      path: {
        type: 'string',
        title: 'SignalK Path',
        description: 'This is used to build the path in Signal K. It will be appended to \'environment\'',
        default: 'inside.salon'
      },
    }
  }

  plugin.start = function (options) {

    function createDeltaMessage (temperature, humidity) {
      var values = [
        {
          'path': 'environment.' + options.path + '.temperature',
          'value': temperature
        }, {
          'path': 'environment.' + options.path + '.humidity',
          'value': humidity
        }
      ];

      return {
        'context': 'vessels.' + app.selfId,
        'updates': [
          {
            'source': {
              'label': plugin.id
            },
            'timestamp': (new Date()).toISOString(),
            'values': values
          }
        ]
      }
    }


    const sht31 = new SHT31()

    // Read SHT31 sensor data
    function readSensorData() {
  	  sht31.readSensorData()
          .then((data) => {
        // temperature_C and humidity are returned by default.
        temperature = data.temperature_C + 273.15;
        humidity = data.humidity;
  
        // create message
        var delta = createDeltaMessage(temperature, humidity)

        // send temperature
        app.handleMessage(plugin.id, delta)

      })
      .catch((err) => {
        console.log(`SHT31 read error: ${err}`);
      });
    }

    readSensorData();
    timer = setInterval(readSensorData, options.rate * 1000);
  }

  plugin.stop = function () {
    if(timer){
      clearInterval(timer);
      timeout = null;
    }
  }

  return plugin
}