HTU21D.cpp

/*
  HTU21D Humidity Sensor Library
  By: Nathan Seidle, since modified by bgbnbigben
  SparkFun Electronics
  Date: v1.1.3: September 22nd, 2013
	    v1.2: April 12, 2019
  License: This code is public domain but you buy me (Nathan Seidle) a beer if you use this and we meet someday (Beerware license).

  This library allows an Arduino to read from the HTU21D low-cost high-precision humidity sensor.
  
  Hardware Setup: The HTU21D lives on the I2C bus. Attach the SDA pin to A4, SCL to A5. If you are using the SparkFun
  breakout board you *do not* need 4.7k pull-up resistors on the bus (they are built-in).

  Datasheet: https://cdn-shop.adafruit.com/datasheets/1899_HTU21D.pdf

  Software:
  Call HTU21D.Begin() in setup.
  HTU21D.SetResolution(byte: 0b.76543210) sets the resolution of the readings.
  HTU21D.check_crc(message, check_value) verifies the 8-bit CRC generated by the sensor
  HTU21D.read_user_register() returns the user register. Used to set resolution.
*/
#include <Bridge.h>
#include <Console.h>
#include <I2C.h>

#include "HTU21D.h"
#include "GreenhouseLibraries.h"

HTU21D::HTU21D() : _inFlight(false), _wireValue(0) {}

/* Start I2C communication, and also issues a soft reset command to the humidity sensor (p12)
 *
 * Uses the global default I2c port if none specified.
 */
void HTU21D::begin(const I2C& wirePort) {
  _inFlight = false;
  _i2cPort = &wirePort; //Grab which port the user wants us to use
  _i2cPort->begin();
  _i2cPort->write(HTU21D_ADDRESS, 0xFE); // Write soft reset
}

/** Initiates a new reading, if one currently is not in flight */
inline uint8_t HTU21D::triggerReading(byte cmd) {
  if (!_inFlight) {
    _inFlight = true;
    return _i2cPort->write(HTU21D_ADDRESS, cmd);
  }
}

/** Initiates a NO HOLD MASTER temperature reading. It is asynchronous. */
uint8_t HTU21D::triggerTemperatureReading() {
  return triggerReading(TRIGGER_TEMP_MEASURE_NOHOLD);
}

/** Initiates a NO HOLD MASTER humidity reading. It is asynchronous. */
uint8_t HTU21D::triggerHumidityReading() {
  return triggerReading(TRIGGER_HUMD_MEASURE_NOHOLD);
}

/** Checks to see if the result of the last requested humidity reading has been completed. */
bool HTU21D::isConversionComplete() {
  if (!_inFlight) return true;

  // resp will be 3 bytes, of the form {msb, lsb|status, checksum}
  uint8_t resp[3] = { 0,0,0 };
  if (_i2cPort->read(HTU21D_ADDRESS, 3, resp) != 0) return false;
  _inFlight = false;

  uint16_t rawValue = ((uint16_t)resp[0] << 8) | (uint16_t) resp[1];

  resp[0] = __builtin_avr_insert_bits(0x01234567, resp[0], 0);
  resp[1] = __builtin_avr_insert_bits(0x01234567, resp[1], 0);
  resp[2] = __builtin_avr_insert_bits(0x01234567, resp[2], 0);

  if (crc8(resp, 3) != 0) {
    _wireValue = 0;
  }
  else {
    _wireValue = rawValue & 0xFFFC; // Zero out bits 43 and 44 (p11), the 'status' bits indicating humidity or temperature response.
  }

  return true;
}

/** Gets the humidity from the last wire reading. */
float HTU21D::getHumidity() {
  // Given the raw humidity data, calculate the actual relative humidity
  // rh = wire * (125.0 / 65536.0) - 6.0; //From page 14
  return divideFloatByPow2(_wireValue, 16) * 125 - 6;
}

/** Get the temperature from the last wire reading */
float HTU21D::getTemperature() {
  // Given the raw temperature data, calculate the actual temperature
  // T = wire * (175.72 / 65536.0) - 46.85; //From page 14
  return divideFloatByPow2(_wireValue, 16) * 175.72 - 46.85;
}

// Set sensor resolution
/*******************************************************************************************/
// Sets the sensor resolution to one of four levels, determined by the 0th and 7th bit of "resolution"
// From p13, bit 7 controls RH and bit 0 controls Temperature.
// Use the USER_REGISTER_RESOLUTION_RHXX_TEMPYY values
// Default at power-on is 12bit RH 14bit Temp, and a soft-reset command does NOT modify the existing values.
void HTU21D::setResolution(byte resolution) {
  // Write out what's already there, with the resolution bits both set to 0 and then or'd with the requested resolution.
  // Done inline to prevent the creation of some temporaries in a non-optimising compiler
  writeUserRegister((readUserRegister() & B01111110) | (resolution & B10000001));
}

// Read the user register
byte HTU21D::readUserRegister(void) {
  byte userRegister;

  _i2cPort->write(HTU21D_ADDRESS, READ_USER_REG);
  _i2cPort->read(HTU21D_ADDRESS, sizeof userRegister, &userRegister);

  return userRegister;
}

void HTU21D::writeUserRegister(byte val) {
  _i2cPort->write(HTU21D_ADDRESS, WRITE_USER_REG);
  _i2cPort->write(HTU21D_ADDRESS, val);
}