BME280.js

/*
  BME280.js

  A Node.js I2C module for the Bosch BME280 Humidity, Barometric Pressure, and Temperature Sensor.

  Support is also included for the Bosch BMP280 Barometric Pressure and Temperature Sensor.
*/

'use strict';

class BME280 {

  constructor(options) {
    const i2c = require('i2c-bus');

    this.i2cBusNo = (options && options.hasOwnProperty('i2cBusNo')) ? options.i2cBusNo : 1;    
    this.i2cBus = i2c.openSync(this.i2cBusNo);
    this.i2cAddress = (options && options.hasOwnProperty('i2cAddress')) ? options.i2cAddress : BME280.BME280_DEFAULT_I2C_ADDRESS();

    this.I2C_ADDRESS_B   = 0x76;
    this.I2C_ADDRESS_A   = 0x77;
    this.CHIP_ID         = 0x58;

    this.REGISTER_DIG_T1 = 0x88;
    this.REGISTER_DIG_T2 = 0x8A;
    this.REGISTER_DIG_T3 = 0x8C;

    this.REGISTER_DIG_P1 = 0x8E;
    this.REGISTER_DIG_P2 = 0x90;
    this.REGISTER_DIG_P3 = 0x92;
    this.REGISTER_DIG_P4 = 0x94;
    this.REGISTER_DIG_P5 = 0x96;
    this.REGISTER_DIG_P6 = 0x98;
    this.REGISTER_DIG_P7 = 0x9A;
    this.REGISTER_DIG_P8 = 0x9C;
    this.REGISTER_DIG_P9 = 0x9E;

    this.REGISTER_DIG_H1 = 0xA1;
    this.REGISTER_DIG_H2 = 0xE1;
    this.REGISTER_DIG_H3 = 0xE3;
    this.REGISTER_DIG_H4 = 0xE4;
    this.REGISTER_DIG_H5 = 0xE5;
    this.REGISTER_DIG_H6 = 0xE7;

    this.REGISTER_CHIPID = 0xD0;
    this.REGISTER_RESET  = 0xE0;

    this.REGISTER_CONTROL_HUM   = 0xF2;
    this.REGISTER_CONTROL       = 0xF4;
    this.REGISTER_PRESSURE_DATA = 0xF7;
    this.REGISTER_TEMP_DATA     = 0xFA;
    this.REGISTER_HUMIDITY_DATA = 0xFD;
  }

  init() {
    return new Promise((resolve, reject) => {
      this.i2cBus.writeByte(this.i2cAddress, this.REGISTER_CHIPID, 0, (err) => {
        if(err) {
          return reject(err);
        }
        this.i2cBus.readByte(this.i2cAddress, this.REGISTER_CHIPID, (err, chipId) => {
          if(err) {
            return reject(err);
          }

          else if(chipId !== BME280.CHIP_ID_BME280() &&
                  chipId !== BME280.CHIP_ID1_BMP280() &&
                  chipId !== BME280.CHIP_ID2_BMP280() &&
                  chipId !== BME280.CHIP_ID3_BMP280()) {
            return reject(`Unexpected BMx280 chip ID: 0x${chipId.toString(16)}`);
          }

          else {
            console.log(`Found BMx280 chip ID 0x${chipId.toString(16)} on bus i2c-${this.i2cBusNo}, address 0x${this.i2cAddress.toString(16)}`);
            this.loadCalibration((err) => {
              if(err) {
                return reject(err);
              }

              // Humidity 16x oversampling
              //
              this.i2cBus.writeByte(this.i2cAddress, this.REGISTER_CONTROL_HUM, 0b00000101, (err) => {
                if(err) {
                  return reject(err);
                }

                // Temperture/pressure 16x oversampling, normal mode
                //
                this.i2cBus.writeByte(this.i2cAddress, this.REGISTER_CONTROL, 0b10110111, (err) => {
                  return err ? reject(err) : resolve(chipId);
                });
              });
            });
          }
        });
      });
    });
  }

  // reset()
  //
  // Perform a power-on reset procedure. You will need to call init() following a reset()
  //
  reset() {
    return new Promise((resolve, reject) => {
      const POWER_ON_RESET_CMD = 0xB6;
      this.i2cBus.writeByte(this.i2cAddress, this.REGISTER_RESET, POWER_ON_RESET_CMD, (err) => {
        return err ? reject(err) : resolve();
      });
    });
  }

  readSensorData() {
    return new Promise((resolve, reject) => {
      if(!this.cal) {
        return reject('You must first call bme280.init()');
      }

      // Grab temperature, humidity, and pressure in a single read
      //
      this.i2cBus.readI2cBlock(this.i2cAddress, this.REGISTER_PRESSURE_DATA, 8, new Buffer(8), (err, bytesRead, buffer) => {
        if(err) {
          return reject(err);
        }

        // Temperature (temperature first since we need t_fine for pressure and humidity)
        //
        let adc_T = BME280.uint20(buffer[3], buffer[4], buffer[5]);
        let tvar1 = ((((adc_T >> 3) - (this.cal.dig_T1 << 1))) * this.cal.dig_T2) >> 11;
        let tvar2  = (((((adc_T >> 4) - this.cal.dig_T1) * ((adc_T >> 4) - this.cal.dig_T1)) >> 12) * this.cal.dig_T3) >> 14;
        let t_fine = tvar1 + tvar2;

        let temperature_C = ((t_fine * 5 + 128) >> 8) / 100;

        // Pressure
        //
        let adc_P = BME280.uint20(buffer[0], buffer[1], buffer[2]);
        let pvar1 = t_fine / 2 - 64000;
        let pvar2 = pvar1 * pvar1 * this.cal.dig_P6 / 32768;
        pvar2 = pvar2 + pvar1 * this.cal.dig_P5 * 2;
        pvar2 = pvar2 / 4 + this.cal.dig_P4 * 65536;
        pvar1 = (this.cal.dig_P3 * pvar1 * pvar1 / 524288 + this.cal.dig_P2 * pvar1) / 524288;
        pvar1 = (1 + pvar1 / 32768) * this.cal.dig_P1;

        let pressure_hPa = 0;

        if(pvar1 !== 0) {
          let p = 1048576 - adc_P;
          p = ((p - pvar2 / 4096) * 6250) / pvar1;
          pvar1 = this.cal.dig_P9 * p * p / 2147483648;
          pvar2 = p * this.cal.dig_P8 / 32768;
          p = p + (pvar1 + pvar2 + this.cal.dig_P7) / 16;

          pressure_hPa = p / 100;
        }

        // Humidity (available on the BME280, will be zero on the BMP280 since it has no humidity sensor)
        //
        let adc_H = BME280.uint16(buffer[6], buffer[7]);

        let h = t_fine - 76800;
        h = (adc_H - (this.cal.dig_H4 * 64 + this.cal.dig_H5 / 16384 * h)) *
            (this.cal.dig_H2 / 65536 * (1 + this.cal.dig_H6 / 67108864 * h * (1 + this.cal.dig_H3 / 67108864 * h)));
        h = h * (1 - this.cal.dig_H1 * h / 524288);

        let humidity = (h > 100) ? 100 : (h < 0 ? 0 : h);

        resolve({
          temperature_C : temperature_C,
          humidity      : humidity,
          pressure_hPa  : pressure_hPa
        });
      });
    });
  }

  loadCalibration(callback) {
    this.i2cBus.readI2cBlock(this.i2cAddress, this.REGISTER_DIG_T1, 24, new Buffer(24), (err, bytesRead, buffer) => {
      let h1   = this.i2cBus.readByteSync(this.i2cAddress, this.REGISTER_DIG_H1);
      let h2   = this.i2cBus.readWordSync(this.i2cAddress, this.REGISTER_DIG_H2);
      let h3   = this.i2cBus.readByteSync(this.i2cAddress, this.REGISTER_DIG_H3);
      let h4   = this.i2cBus.readByteSync(this.i2cAddress, this.REGISTER_DIG_H4);
      let h5   = this.i2cBus.readByteSync(this.i2cAddress, this.REGISTER_DIG_H5);
      let h5_1 = this.i2cBus.readByteSync(this.i2cAddress, this.REGISTER_DIG_H5 + 1);
      let h6   = this.i2cBus.readByteSync(this.i2cAddress, this.REGISTER_DIG_H6);

      this.cal = {
        dig_T1: BME280.uint16(buffer[1], buffer[0]),
        dig_T2: BME280.int16(buffer[3], buffer[2]),
        dig_T3: BME280.int16(buffer[5], buffer[4]),

        dig_P1: BME280.uint16(buffer[7], buffer[6]),
        dig_P2: BME280.int16(buffer[9], buffer[8]),
        dig_P3: BME280.int16(buffer[11], buffer[10]),
        dig_P4: BME280.int16(buffer[13], buffer[12]),
        dig_P5: BME280.int16(buffer[15], buffer[14]),
        dig_P6: BME280.int16(buffer[17], buffer[16]),
        dig_P7: BME280.int16(buffer[19], buffer[18]),
        dig_P8: BME280.int16(buffer[21], buffer[20]),
        dig_P9: BME280.int16(buffer[23], buffer[22]),

        dig_H1: h1,
        dig_H2: h2,
        dig_H3: h3,
        dig_H4: (h4 << 4) | (h5 & 0xF),
        dig_H5: (h5_1 << 4) | (h5 >> 4),
        dig_H6: h6
      };

      //console.log('BME280 cal = ' + JSON.stringify(this.cal, null, 2));
      callback();
    });
  }

  static BME280_DEFAULT_I2C_ADDRESS() {
    return 0x77;
  }

  static CHIP_ID1_BMP280() {
    return 0x56;
  }

  static CHIP_ID2_BMP280() {
    return 0x57;
  }

  static CHIP_ID3_BMP280() {
    return 0x58;
  }

  static CHIP_ID_BME280() {
    return 0x60;
  }

  static int16(msb, lsb) {
    let val = BME280.uint16(msb, lsb);
    return val > 32767 ? (val - 65536) : val;
  }

  static uint16(msb, lsb) {
    return msb << 8 | lsb;
  }

  static uint20(msb, lsb, xlsb) {
    return ((msb << 8 | lsb) << 8 | xlsb) >> 4;
  }

  static convertCelciusToFahrenheit(c) { 
    return c * 9 / 5 + 32;
  }

  static convertHectopascalToInchesOfMercury(hPa) {
    return hPa * 0.02952998751;
  }

  static convertMetersToFeet(m) {
    return m * 3.28084;
  }

  static calculateHeatIndexCelcius(temperature_C, humidity) {
    return -8.784695 + 1.61139411 * temperature_C + 2.33854900 * humidity +
           -0.14611605 * temperature_C * humidity + -0.01230809 * Math.pow(temperature_C, 2) +
           -0.01642482 * Math.pow(humidity, 2) + 0.00221173 * Math.pow(temperature_C, 2) * humidity +
           0.00072546 * temperature_C * Math.pow(humidity, 2) +
           -0.00000358 * Math.pow(temperature_C, 2) * Math.pow(humidity, 2);
  }

  static calculateDewPointCelcius(temperature_C, humidity) {
    return 243.04 * (Math.log(humidity/100.0) + ((17.625 * temperature_C)/(243.04 + temperature_C))) / 
           (17.625 - Math.log(humidity/100.0) - ((17.625 * temperature_C)/(243.04 + temperature_C)));
  }

  static calculateAltitudeMeters(pressure_hPa, seaLevelPressure_hPa) {
    if(!seaLevelPressure_hPa) {
      seaLevelPressure_hPa = 1013.25;
    }

    return (1.0 - Math.pow(pressure_hPa / seaLevelPressure_hPa, (1 / 5.2553))) * 145366.45 * 0.3048;
  }

}

module.exports = BME280;