scd4x-sensor.js

'use strict';

const i2c = require('i2c-bus');
const { setTimeout } = require('timers/promises');

class SCD4X {
  static #ADDRESS = 0x62;

  // コマンド定義
  static #START_PERIODIC_MEASUREMENT_COMMAND = 0x21b1;
  static #READ_MEASUREMENT_COMMAND = 0xec05;
  static #STOP_PERIODIC_MEASUREMENT_COMMAND = 0x3f86;
  static #GET_SERIAL_NUMBER_COMMAND = 0x3682;

  static #COMMAND_LENGTH = 2;

  #bus;
  #serialNumber;

  constructor() {
    this.#bus = null;
    this.#serialNumber = null;
  }

  get serialNumber() { return this.#serialNumber; }

  initialize() {
    return i2c.openPromisified(1)
      .then(bus => {
        this.#bus = bus;
        return this.#stopPeriodicMeasurement();
      })
      .then(() => {
        return this.#getSerialNumber();
      })
      .then(() => {
        return this.#startPeriodicMeasurement();
      })
  }

  readSensorData() {
    return this.#readMeasurement()
  }

  static #toBuffer(command) {
    return Buffer.from([command >> 8, command & 0xff])
  }

  #sendCommand(command) {
    return this.#bus.i2cWrite(SCD4X.#ADDRESS, SCD4X.#COMMAND_LENGTH, SCD4X.#toBuffer(command));
  }

  #read(command, bufferLength) {
    const buf = Buffer.alloc(bufferLength);

    return this.#bus.i2cWrite(SCD4X.#ADDRESS, SCD4X.#COMMAND_LENGTH, SCD4X.#toBuffer(command))
      .then(() => {
        return this.#bus.i2cRead(SCD4X.#ADDRESS, buf.length, buf)
      })
  }

  #getSerialNumber() {
    return this.#read(SCD4X.#GET_SERIAL_NUMBER_COMMAND, 9)
      .then(res => {
        this.#serialNumber = '';

        const buf = res.buffer;
        const values = [buf.readUInt16BE(0), buf.readUInt16BE(3), buf.readUInt16BE(6)];
        values.forEach(value => {
          this.#serialNumber += value.toString(16);
        })

        return setTimeout(10);
      })
  }

  #startPeriodicMeasurement() {
    return this.#sendCommand(SCD4X.#START_PERIODIC_MEASUREMENT_COMMAND);
  }

  #readMeasurement() {
    const toCO2 = (value => value);
    const toTemperature = (value => -45 + 175 * value / 65536)
    const toHumidity = (value => 100 * value / 65536)

    return this.#read(SCD4X.#READ_MEASUREMENT_COMMAND, 9)
      .then(res => {
        return {
          co2: toCO2(res.buffer.readUInt16BE(0)),
          temperature: toTemperature(res.buffer.readUInt16BE(3)),
          humidity: toHumidity(res.buffer.readUInt16BE(6)),
        }
      })
  }

  #stopPeriodicMeasurement() {
    return this.#sendCommand(SCD4X.#STOP_PERIODIC_MEASUREMENT_COMMAND)
      .then(() => {
        return setTimeout(1000);
      })
  }
}

module.exports = SCD4X;