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@lucadentella
lucadentella committed Oct 8, 2017
1 parent e67ea98 commit a80b0a1
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7 changes: 7 additions & 0 deletions component.mk
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#
# Component Makefile
#

COMPONENT_SRCDIRS := .
COMPONENT_ADD_INCLUDEDIRS := .
COMPONENT_PRIV_INCLUDEDIRS :=
232 changes: 232 additions & 0 deletions htu21d.c
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/*
* HTU21D Component
*
* esp-idf component to interface with HTU21D humidity and temperature sensor
* by TE Connectivity (http://www.te.com/usa-en/product-CAT-HSC0004.html)
*
* Luca Dentella, www.lucadentella.it
*/


// Component header file
#include "htu21d.h"

int htu21d_init(i2c_port_t port, int sda_pin, int scl_pin, gpio_pullup_t sda_internal_pullup, gpio_pullup_t scl_internal_pullup) {

esp_err_t ret;
_port = port;

// setup i2c controller
i2c_config_t conf;
conf.mode = I2C_MODE_MASTER;
conf.sda_io_num = sda_pin;
conf.scl_io_num = scl_pin;
conf.sda_pullup_en = sda_internal_pullup;
conf.scl_pullup_en = scl_internal_pullup;
conf.master.clk_speed = 100000;
ret = i2c_param_config(port, &conf);
if(ret != ESP_OK) return HTU21D_ERR_CONFIG;

// install the driver
ret = i2c_driver_install(port, I2C_MODE_MASTER, 0, 0, 0);
if(ret != ESP_OK) return HTU21D_ERR_INSTALL;

// verify if a sensor is present
i2c_cmd_handle_t cmd = i2c_cmd_link_create();
i2c_master_start(cmd);
i2c_master_write_byte(cmd, (HTU21D_ADDR << 1) | I2C_MASTER_WRITE, true);
i2c_master_stop(cmd);
if(i2c_master_cmd_begin(port, cmd, 1000 / portTICK_RATE_MS) != ESP_OK)
return HTU21D_ERR_NOTFOUND;

return HTU21D_ERR_OK;
}

float ht21d_read_temperature() {

// get the raw value from the sensor
uint16_t raw_temperature = read_value(TRIGGER_TEMP_MEASURE_NOHOLD);
if(raw_temperature == 0) return -999;

// return the real value, formula in datasheet
return (raw_temperature * 175.72 / 65536.0) - 46.85;
}

float ht21d_read_humidity() {

// get the raw value from the sensor
uint16_t raw_humidity = read_value(TRIGGER_HUMD_MEASURE_NOHOLD);
if(raw_humidity == 0) return -999;

// return the real value, formula in datasheet
return (raw_humidity * 125.0 / 65536.0) - 6.0;
}

uint8_t ht21d_get_resolution() {

uint8_t reg_value = ht21d_read_user_register();
return reg_value & 0b10000001;
}

int ht21d_set_resolution(uint8_t resolution) {

// get the actual resolution
uint8_t reg_value = ht21d_read_user_register();
reg_value &= 0b10000001;

// update the register value with the new resolution
resolution &= 0b10000001;
reg_value |= resolution;

return ht21d_write_user_register(reg_value);
}

int htu21d_soft_reset() {

esp_err_t ret;

// send the command
i2c_cmd_handle_t cmd = i2c_cmd_link_create();
i2c_master_start(cmd);
i2c_master_write_byte(cmd, (HTU21D_ADDR << 1) | I2C_MASTER_WRITE, true);
i2c_master_write_byte(cmd, SOFT_RESET, true);
i2c_master_stop(cmd);
ret = i2c_master_cmd_begin(_port, cmd, 1000 / portTICK_RATE_MS);
i2c_cmd_link_delete(cmd);

switch(ret) {

case ESP_ERR_INVALID_ARG:
return HTU21D_ERR_INVALID_ARG;

case ESP_FAIL:
return HTU21D_ERR_FAIL;

case ESP_ERR_INVALID_STATE:
return HTU21D_ERR_INVALID_STATE;

case ESP_ERR_TIMEOUT:
return HTU21D_ERR_TIMEOUT;
}
return HTU21D_ERR_OK;
}

uint8_t ht21d_read_user_register() {

esp_err_t ret;

// send the command
i2c_cmd_handle_t cmd = i2c_cmd_link_create();
i2c_master_start(cmd);
i2c_master_write_byte(cmd, (HTU21D_ADDR << 1) | I2C_MASTER_WRITE, true);
i2c_master_write_byte(cmd, READ_USER_REG, true);
i2c_master_stop(cmd);
ret = i2c_master_cmd_begin(_port, cmd, 1000 / portTICK_RATE_MS);
i2c_cmd_link_delete(cmd);
if(ret != ESP_OK) return 0;

// receive the answer
uint8_t reg_value;
cmd = i2c_cmd_link_create();
i2c_master_start(cmd);
i2c_master_write_byte(cmd, (HTU21D_ADDR << 1) | I2C_MASTER_READ, true);
i2c_master_read_byte(cmd, &reg_value, 0x01);
i2c_master_stop(cmd);
ret = i2c_master_cmd_begin(_port, cmd, 1000 / portTICK_RATE_MS);
i2c_cmd_link_delete(cmd);
if(ret != ESP_OK) return 0;

return reg_value;
}

int ht21d_write_user_register(uint8_t value) {

esp_err_t ret;

// send the command
i2c_cmd_handle_t cmd = i2c_cmd_link_create();
i2c_master_start(cmd);
i2c_master_write_byte(cmd, (HTU21D_ADDR << 1) | I2C_MASTER_WRITE, true);
i2c_master_write_byte(cmd, WRITE_USER_REG, true);
i2c_master_write_byte(cmd, value, true);
i2c_master_stop(cmd);
ret = i2c_master_cmd_begin(_port, cmd, 1000 / portTICK_RATE_MS);
i2c_cmd_link_delete(cmd);

switch(ret) {

case ESP_ERR_INVALID_ARG:
return HTU21D_ERR_INVALID_ARG;

case ESP_FAIL:
return HTU21D_ERR_FAIL;

case ESP_ERR_INVALID_STATE:
return HTU21D_ERR_INVALID_STATE;

case ESP_ERR_TIMEOUT:
return HTU21D_ERR_TIMEOUT;
}
return HTU21D_ERR_OK;
}

uint16_t read_value(uint8_t command) {

esp_err_t ret;

// send the command
i2c_cmd_handle_t cmd = i2c_cmd_link_create();
i2c_master_start(cmd);
i2c_master_write_byte(cmd, (HTU21D_ADDR << 1) | I2C_MASTER_WRITE, true);
i2c_master_write_byte(cmd, command, true);
i2c_master_stop(cmd);
ret = i2c_master_cmd_begin(_port, cmd, 1000 / portTICK_RATE_MS);
i2c_cmd_link_delete(cmd);
if(ret != ESP_OK) return 0;

// wait for the sensor (50ms)
vTaskDelay(50 / portTICK_RATE_MS);

// receive the answer
uint8_t msb, lsb, crc;
cmd = i2c_cmd_link_create();
i2c_master_start(cmd);
i2c_master_write_byte(cmd, (HTU21D_ADDR << 1) | I2C_MASTER_READ, true);
i2c_master_read_byte(cmd, &msb, 0x00);
i2c_master_read_byte(cmd, &lsb, 0x00);
i2c_master_read_byte(cmd, &crc, 0x01);
i2c_master_stop(cmd);
ret = i2c_master_cmd_begin(_port, cmd, 1000 / portTICK_RATE_MS);
i2c_cmd_link_delete(cmd);
if(ret != ESP_OK) return 0;

uint16_t raw_value = ((uint16_t) msb << 8) | (uint16_t) lsb;
if(!is_crc_valid(raw_value, crc)) printf("CRC invalid\r\n");
return raw_value & 0xFFFC;
}

// verify the CRC, algorithm in the datasheet (see comments below)
bool is_crc_valid(uint16_t value, uint8_t crc) {

// line the bits representing the input in a row (first data, then crc)
uint32_t row = (uint32_t)value << 8;
row |= crc;

// polynomial = x^8 + x^5 + x^4 + 1
// padded with zeroes corresponding to the bit length of the CRC
uint32_t divisor = (uint32_t)0x988000;

for (int i = 0 ; i < 16 ; i++) {

// if the input bit above the leftmost divisor bit is 1,
// the divisor is XORed into the input
if (row & (uint32_t)1 << (23 - i)) row ^= divisor;

// the divisor is then shifted one bit to the right
divisor >>= 1;
}

// the remainder should equal zero if there are no detectable errors
return (row == 0);
}

64 changes: 64 additions & 0 deletions htu21d.h
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/*
* HTU21D Component
*
* esp-idf component to interface with HTU21D humidity and temperature sensor
* by TE Connectivity (http://www.te.com/usa-en/product-CAT-HSC0004.html)
*
* Luca Dentella, www.lucadentella.it
*/


// Error library
#include "esp_err.h"

// I2C driver
#include "driver/i2c.h"

// FreeRTOS (for delay)
#include "freertos/task.h"


#ifndef __ESP_HTU21D_H__
#define __ESP_HTU21D_H__

// sensor address
#define HTU21D_ADDR 0x40

// HTU21D commands
#define TRIGGER_TEMP_MEASURE_HOLD 0xE3
#define TRIGGER_HUMD_MEASURE_HOLD 0xE5
#define TRIGGER_TEMP_MEASURE_NOHOLD 0xF3
#define TRIGGER_HUMD_MEASURE_NOHOLD 0xF5
#define WRITE_USER_REG 0xE6
#define READ_USER_REG 0xE7
#define SOFT_RESET 0xFE

// return values
#define HTU21D_ERR_OK 0x00
#define HTU21D_ERR_CONFIG 0x01
#define HTU21D_ERR_INSTALL 0x02
#define HTU21D_ERR_NOTFOUND 0x03
#define HTU21D_ERR_INVALID_ARG 0x04
#define HTU21D_ERR_FAIL 0x05
#define HTU21D_ERR_INVALID_STATE 0x06
#define HTU21D_ERR_TIMEOUT 0x07

// variables
i2c_port_t _port;

// functions
int htu21d_init(i2c_port_t port, int sda_pin, int scl_pin, gpio_pullup_t sda_internal_pullup, gpio_pullup_t scl_internal_pullup);
float ht21d_read_temperature();
float ht21d_read_humidity();
uint8_t ht21d_get_resolution();
int ht21d_set_resolution(uint8_t resolution);
int htu21d_soft_reset();

// helper functions
uint8_t ht21d_read_user_register();
int ht21d_write_user_register(uint8_t value);
uint16_t read_value(uint8_t command);
bool is_crc_valid(uint16_t value, uint8_t crc);


#endif // __ESP_HTU21D_H__

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