Sensirion SHT3x temperature / humidity sensor codec (DETWS_ENABLE_SHT3X). More...

#include <stddef.h>
#include <stdint.h>

Macros
#define	SHT3X_CMD_SINGLE_HIGH 0x2400
	high repeatability, no clock stretching

#define	SHT3X_CMD_SINGLE_MED 0x240B
	medium repeatability

#define	SHT3X_CMD_SINGLE_LOW 0x2416
	low repeatability

#define	SHT3X_CMD_SOFT_RESET 0x30A2
	soft reset

#define	SHT3X_CMD_READ_STATUS 0xF32D
	read the status register

#define	SHT3X_CMD_HEATER_ON 0x306D
	enable the on-chip heater

#define	SHT3X_CMD_HEATER_OFF 0x3066
	disable the on-chip heater

Functions
uint8_t	sht3x_crc8 (const uint8_t *data, size_t len)
	Sensirion CRC-8 (poly 0x31, init 0xFF) over `len` bytes.

int32_t	sht3x_temp_mc (uint16_t raw)
	Convert a raw 16-bit temperature tick to milli-degrees Celsius.

int32_t	sht3x_rh_mpct (uint16_t raw)
	Convert a raw 16-bit humidity tick to milli-percent relative humidity (0..100000).

bool	sht3x_parse (const uint8_t resp[6], int32_t temp_mc, int32_t rh_mpct)
	Decode a six-byte single-shot response (T msb/lsb/crc, RH msb/lsb/crc). Verifies both CRC-8 words, then fills `temp_mc` and `rh_mpct` (either may be null).

bool	sht3x_begin (uint8_t addr)
	Soft-reset the SHT3x at `addr` over I2C.

bool	sht3x_read (int32_t temp_mc, int32_t rh_mpct)
	Trigger a single-shot high-repeatability measurement, read + verify the six bytes, and return the temperature (milli-C) and humidity (milli-RH).

Detailed Description

Sensirion SHT3x temperature / humidity sensor codec (DETWS_ENABLE_SHT3X).

The SHT3x (SHT30 / SHT31 / SHT35) answers a single-shot measurement command with six bytes: a 16-bit temperature word + its CRC-8, then a 16-bit humidity word + its CRC-8. The CRC is the Sensirion CRC-8 (polynomial 0x31, init 0xFF, no reflection, no final XOR; the datasheet check value is 0xBEEF -> 0x92). Raw ticks convert linearly: T[C] = -45 + 175 * raw / 65535 RH[%] = 100 * raw / 65535

To stay heap- and float-printf-free, the results are returned as signed integer milli-units (milli-degrees C, milli-percent RH). The CRC check and the conversion are pure and host-tested; only the command write / data read touches I2C.

A cheap solder-and-bench-test breakout (GY-SHT31 etc.): read it, bridge the reading onto the network as telemetry.

Author: Douglas Quigg (dstroy0)

Date: 2026

Definition in file sht3x.h.

Macro Definition Documentation

◆ SHT3X_CMD_SINGLE_HIGH

#define SHT3X_CMD_SINGLE_HIGH 0x2400

high repeatability, no clock stretching

Definition at line 33 of file sht3x.h.

◆ SHT3X_CMD_SINGLE_MED

#define SHT3X_CMD_SINGLE_MED 0x240B

medium repeatability

Definition at line 34 of file sht3x.h.

◆ SHT3X_CMD_SINGLE_LOW

#define SHT3X_CMD_SINGLE_LOW 0x2416

low repeatability

Definition at line 35 of file sht3x.h.

◆ SHT3X_CMD_SOFT_RESET

#define SHT3X_CMD_SOFT_RESET 0x30A2

soft reset

Definition at line 36 of file sht3x.h.

◆ SHT3X_CMD_READ_STATUS

#define SHT3X_CMD_READ_STATUS 0xF32D

read the status register

Definition at line 37 of file sht3x.h.

◆ SHT3X_CMD_HEATER_ON

#define SHT3X_CMD_HEATER_ON 0x306D

enable the on-chip heater

Definition at line 38 of file sht3x.h.

◆ SHT3X_CMD_HEATER_OFF

#define SHT3X_CMD_HEATER_OFF 0x3066

disable the on-chip heater

Definition at line 39 of file sht3x.h.

Function Documentation

◆ sht3x_crc8()

uint8_t sht3x_crc8	(	const uint8_t *	data,
		size_t	len
	)

Sensirion CRC-8 (poly 0x31, init 0xFF) over len bytes.

◆ sht3x_temp_mc()

int32_t sht3x_temp_mc ( uint16_t raw )

Convert a raw 16-bit temperature tick to milli-degrees Celsius.

◆ sht3x_rh_mpct()

int32_t sht3x_rh_mpct ( uint16_t raw )

Convert a raw 16-bit humidity tick to milli-percent relative humidity (0..100000).

◆ sht3x_parse()

bool sht3x_parse	(	const uint8_t	resp[6],
		int32_t *	temp_mc,
		int32_t *	rh_mpct
	)

Decode a six-byte single-shot response (T msb/lsb/crc, RH msb/lsb/crc). Verifies both CRC-8 words, then fills temp_mc and rh_mpct (either may be null).

Returns: false if a CRC does not match (a corrupt read).

◆ sht3x_begin()

bool sht3x_begin ( uint8_t addr )

Soft-reset the SHT3x at addr over I2C.

Returns: true if it acknowledged.

◆ sht3x_read()

bool sht3x_read	(	int32_t *	temp_mc,
		int32_t *	rh_mpct
	)

Trigger a single-shot high-repeatability measurement, read + verify the six bytes, and return the temperature (milli-C) and humidity (milli-RH).

Returns: false on I2C or CRC error.

Macros

Functions