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168 lines
5.1 KiB
168 lines
5.1 KiB
// -----------------------------------------------------------------------------
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// SI7021 / HTU21D Sensor over I2C
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// Copyright (C) 2017-2018 by Xose Pérez <xose dot perez at gmail dot com>
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// -----------------------------------------------------------------------------
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#if SENSOR_SUPPORT && SI7021_SUPPORT
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#pragma once
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#include "Arduino.h"
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#include "I2CSensor.h"
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#define SI7021_SCL_FREQUENCY 200
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#define SI7021_CHIP_SI7021 0x15
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#define SI7021_CHIP_HTU21D 0x32
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#define SI7021_CMD_TMP_HOLD 0xE3
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#define SI7021_CMD_HUM_HOLD 0xE5
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#define SI7021_CMD_TMP_NOHOLD 0xF3
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#define SI7021_CMD_HUM_NOHOLD 0xF5
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PROGMEM const char si7021_chip_si7021_name[] = "SI7021";
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PROGMEM const char si7021_chip_htu21d_name[] = "HTU21D";
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class SI7021Sensor : public I2CSensor {
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public:
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// ---------------------------------------------------------------------
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// Public
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// ---------------------------------------------------------------------
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SI7021Sensor(): I2CSensor() {
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_sensor_id = SENSOR_SI7021_ID;
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}
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// ---------------------------------------------------------------------
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// Sensor API
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// ---------------------------------------------------------------------
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// Initialization method, must be idempotent
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void begin() {
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if (!_dirty) return;
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_init();
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_dirty = !_ready;
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}
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// Descriptive name of the sensor
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String description() {
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char name[10];
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strncpy_P(name,
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_chip == SI7021_CHIP_SI7021 ?
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si7021_chip_si7021_name :
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si7021_chip_htu21d_name,
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sizeof(name)
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);
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char buffer[25];
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snprintf(buffer, sizeof(buffer), "%s @ I2C (0x%02X)", name, _address);
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return String(buffer);
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}
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// Descriptive name of the slot # index
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String slot(unsigned char index) {
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return description();
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};
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// Type for slot # index
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unsigned char type(unsigned char index) {
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if (index == 0) return MAGNITUDE_TEMPERATURE;
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if (index == 1) return MAGNITUDE_HUMIDITY;
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return MAGNITUDE_NONE;
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}
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// Pre-read hook (usually to populate registers with up-to-date data)
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void pre() {
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_error = SENSOR_ERROR_UNKNOWN_ID;
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if (_chip == 0) return;
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_error = SENSOR_ERROR_OK;
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double value;
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value = _read(SI7021_CMD_TMP_NOHOLD);
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if (_error != SENSOR_ERROR_OK) return;
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_temperature = (175.72 * value / 65536) - 46.85;
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value = _read(SI7021_CMD_HUM_NOHOLD);
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if (_error != SENSOR_ERROR_OK) return;
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value = (125.0 * value / 65536) - 6;
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_humidity = constrain(value, 0, 100);
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}
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// Current value for slot # index
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double value(unsigned char index) {
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if (index == 0) return _temperature;
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if (index == 1) return _humidity;
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return 0;
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}
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protected:
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// ---------------------------------------------------------------------
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// Protected
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// ---------------------------------------------------------------------
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void _init() {
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// I2C auto-discover
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unsigned char addresses[] = {0x40};
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_address = _begin_i2c(_address, sizeof(addresses), addresses);
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if (_address == 0) return;
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// Check device
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i2c_write_uint8(_address, 0xFC, 0xC9);
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_chip = i2c_read_uint8(_address);
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if ((_chip != SI7021_CHIP_SI7021) & (_chip != SI7021_CHIP_HTU21D)) {
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_count = 0;
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i2cReleaseLock(_address);
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_previous_address = 0;
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_error = SENSOR_ERROR_UNKNOWN_ID;
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// Setting _address to 0 forces auto-discover
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// This might be necessary at this stage if there is a
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// different sensor in the hardcoded address
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_address = 0;
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} else {
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_count = 2;
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}
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_ready = true;
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}
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unsigned int _read(uint8_t command) {
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// Request measurement
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i2c_write_uint8(_address, command);
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// When not using clock stretching (*_NOHOLD commands) delay here
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// is needed to wait for the measurement.
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// According to datasheet the max. conversion time is ~22ms
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unsigned long start = millis();
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while (millis() - start < 50) delay(1);
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// Clear the last to bits of LSB to 00.
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// According to datasheet LSB of RH is always xxxxxx10
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unsigned int value = i2c_read_uint16(_address) & 0xFFFC;
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// We should be checking there are no pending bytes in the buffer
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// and raise a CRC error if there are
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_error = SENSOR_ERROR_OK;
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return value;
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}
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unsigned char _chip;
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double _temperature = 0;
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double _humidity = 0;
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};
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#endif // SENSOR_SUPPORT && SI7021_SUPPORT
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