mhsw-espurna/code/espurna/sensors/SI7021Sensor.h

// -----------------------------------------------------------------------------
// SI7021 / HTU21D Sensor over I2C
// Copyright (C) 2017 by Xose Pérez <xose dot perez at gmail dot com>
// -----------------------------------------------------------------------------

#pragma once

#include "Arduino.h"
#include "I2CSensor.h"
#if I2C_USE_BRZO
#include <brzo_i2c.h>
#else
#include <Wire.h>
#endif

#define SI7021_SCL_FREQUENCY    200

#define SI7021_CHIP_SI7021      0x15
#define SI7021_CHIP_HTU21D      0x32

#define SI7021_CMD_TMP_HOLD     0xE3
#define SI7021_CMD_HUM_HOLD     0xE5
#define SI7021_CMD_TMP_NOHOLD   0xF3
#define SI7021_CMD_HUM_NOHOLD   0xF5

class SI7021Sensor : public I2CSensor {

    public:

        // ---------------------------------------------------------------------
        // Public
        // ---------------------------------------------------------------------

        SI7021Sensor(): I2CSensor() {
            _sensor_id = SENSOR_SI7021_ID;
        }

        // ---------------------------------------------------------------------
        // Sensor API
        // ---------------------------------------------------------------------

        // Initialization method, must be idempotent
        void begin() {

            if (!_dirty) return;
            _dirty = false;

            // I2C auto-discover
            unsigned char addresses[] = {0x40};
            _address = _begin_i2c(_address, sizeof(addresses), addresses);
            if (_address == 0) return;

            // Check device
            #if I2C_USE_BRZO
                uint8_t buffer[2] = {0xFC, 0xC9};
                brzo_i2c_start_transaction(_address, SI7021_SCL_FREQUENCY);
                brzo_i2c_write(buffer, 2, false);
                brzo_i2c_read(buffer, 1, false);
                brzo_i2c_end_transaction();
                _chip = buffer[0];
            #else
                Wire.beginTransmission(_address);
                Wire.write(0xFC);
                Wire.write(0xC9);
                Wire.endTransmission();
                Wire.requestFrom(_address, (unsigned char) 1);
                _chip = Wire.read();
            #endif

            if ((_chip != SI7021_CHIP_SI7021) & (_chip != SI7021_CHIP_HTU21D)) {
                i2cReleaseLock(_address);
                _error = SENSOR_ERROR_UNKNOWN_ID;
            } else {
                _count = 2;
            }

        }

        // Descriptive name of the sensor
        String description() {
            char buffer[25];
            snprintf(buffer, sizeof(buffer), "%s @ I2C (0x%02X)", chipAsString().c_str(), _address);
            return String(buffer);
        }

        // Type for slot # index
        magnitude_t type(unsigned char index) {
            if (index < _count) {
                _error = SENSOR_ERROR_OK;
                if (index == 0) return MAGNITUDE_TEMPERATURE;
                if (index == 1) return MAGNITUDE_HUMIDITY;
            }
            _error = SENSOR_ERROR_OUT_OF_RANGE;
            return MAGNITUDE_NONE;
        }

        // Current value for slot # index
        double value(unsigned char index) {
            if (index < _count) {
                _error = SENSOR_ERROR_OK;
                double value;
                if (index == 0) {
                    value = read(SI7021_CMD_TMP_NOHOLD);
                    value = (175.72 * value / 65536) - 46.85;
                }
                if (index == 1) {
                    value = read(SI7021_CMD_HUM_NOHOLD);
                    value = (125.0 * value / 65536) - 6;
                    value = constrain(value, 0, 100);
                }
                return value;
            }
            _error = SENSOR_ERROR_OUT_OF_RANGE;
            return 0;
        }

    protected:

        // ---------------------------------------------------------------------
        // Protected
        // ---------------------------------------------------------------------

        unsigned int read(uint8_t command) {

            unsigned char bytes = (command == 0xE0) ? 2 : 3;

            #if I2C_USE_BRZO
                uint8_t buffer[2] = {command, 0x00};
                brzo_i2c_start_transaction(_address, SI7021_SCL_FREQUENCY);
                brzo_i2c_write(buffer, 1, false);
            #else
                Wire.beginTransmission(_address);
                Wire.write(command);
                Wire.endTransmission();
            #endif

            // When not using clock stretching (*_NOHOLD commands) delay here
            // is needed to wait for the measurement.
            // According to datasheet the max. conversion time is ~22ms
            unsigned long start = millis();
            while (millis() - start < 50) delay(1);

            #if I2C_USE_BRZO
                brzo_i2c_read(buffer, 2, false);
                brzo_i2c_end_transaction();
                unsigned int msb = buffer[0];
                unsigned int lsb = buffer[1];
            #else
                Wire.requestFrom(_address, bytes);
                if (Wire.available() != bytes) {
                    _error = SENSOR_ERROR_CRC;
                    return 0;
                }
                unsigned int msb = Wire.read();
                unsigned int lsb = Wire.read();
            #endif

            // Clear the last to bits of LSB to 00.
            // According to datasheet LSB of RH is always xxxxxx10
            lsb &= 0xFC;

            unsigned int value = (msb << 8) | lsb;

            _error = SENSOR_ERROR_OK;
            return value;

        }

        String chipAsString() {
            if (_chip == SI7021_CHIP_SI7021) return String("SI7021");
            if (_chip == SI7021_CHIP_HTU21D) return String("HTU21D");
            return String("Unknown");
        }

        unsigned char _chip;

};