esp32-sensornode/main/si7021.cpp

/*
 * si7021 library
 * SI7021 Temperature and Humidity Sensor @ ESP32 i2c
 *
 * copyright: Jannik Beyerstedt | http://jannikbeyerstedt.de | code@jannikbeyerstedt.de
 * license: http://www.gnu.org/licenses/gpl-3.0.txt GPLv3 License
 */

#include <Arduino.h>
#include <Wire.h>

#include "si7021.hpp"

/**
 * Constuctor of the SI7021 sensor wrapper
 */
Si7021::Si7021(void) {
  _i2caddr = SI7021_DEFAULT_ADDRESS;
}

/**
 * Start the I2C interface
 *    Attention: leave at least 25 ms power up time before the first measurement
 */
bool Si7021::begin(void) {
  Wire.begin();
  Wire.setClock(200000);

  reset();

  if (readRegister8(SI7021_READRHT_REG_CMD) != 0x3A) {
    return false;
  }

  return true;
}

/**
 * Send a reset command to the sensor
 */
void Si7021::reset(void) {
  Wire.beginTransmission(_i2caddr);
  Wire.write((uint8_t)SI7021_RESET_CMD);
  Wire.endTransmission(true);
  delay(10);  // SI7021 reset time
}

/**
 * Initiate a humidity and temperature measurement
 *    Get the values from the public variables temperature and humudity
 *
 * @return  true, if successful measurement
 */
bool Si7021::measure(void) {
  uint8_t chxsum;
  uint8_t cnt;

  // TRIGGER HUMIDITY MEASUREMENT AND GET VALUE
  Wire.beginTransmission(_i2caddr);
  Wire.write((uint8_t)SI7021_MEASRH_NOHOLD_CMD);
  Wire.endTransmission(true);  // true, otherwise the read will not work

  delay(23);  // wait for the Conversion Time of the Sensor
  cnt = Wire.requestFrom(_i2caddr, 3);
  if (cnt < 3) {
    // Serial.printf("[ERROR] SI7021 humi, only %d bytes received\n", cnt);
    return false;
  }

  uint16_t hum_raw = Wire.read();
  hum_raw <<= 8;
  hum_raw |= Wire.read();
  chxsum = Wire.read();

  this->humidity = hum_raw;
  this->humidity *= 125;
  this->humidity /= 65536;
  this->humidity -= 6;

  // GET TEMPERATURE VALUE OF PREVIOUS HUMIDITY MEASUREMENT
  Wire.beginTransmission(_i2caddr);
  Wire.write((uint8_t)SI7021_READPREVTEMP_CMD);
  Wire.endTransmission(true);  // true, otherwise the read will not work

  cnt = Wire.requestFrom(_i2caddr, 3);
  if (cnt < 3) {
    // Serial.printf("[ERROR] SI7021 temp, only %d bytes received\n", cnt);
    return false;
  }
  uint16_t temp_raw = Wire.read();
  temp_raw <<= 8;
  temp_raw |= Wire.read();
  chxsum = Wire.read();

  this->temperature = temp_raw;
  this->temperature *= 175.72;
  this->temperature /= 65536;
  this->temperature -= 46.85;

  return true;
}

// void Si7021::writeRegister8(uint8_t reg, uint8_t value) {
//   // TODO: Test
//   Wire.beginTransmission(_i2caddr);
//   Wire.write((uint8_t)reg);
//   Wire.write((uint8_t)value);
//   Wire.endTransmission();
// }

uint8_t Si7021::readRegister8(uint8_t reg) {
  uint8_t value;
  Wire.beginTransmission(_i2caddr);
  Wire.write((uint8_t)reg);
  Wire.endTransmission(true);  // true, otherwise the value does not get read

  Wire.requestFrom(_i2caddr, 1);
  value = Wire.read();

  return value;
}