aht20.h File Reference

Driver interface for the AHT20 humidity and temperature sensor. More...

#include "stdint.h"
#include "stddef.h"

Go to the source code of this file.

Data Structures
struct	AHT20_HandleTypeDef
	AHT20 driver handle. More...

Macros
#define	AHT20_ADDRESS   (0x38 << 1)
	AHT20 I2C base address (7-bit = 0x38, shifted left for HAL).
#define	AHT20_CMD_STATUS   0x71
	Command byte: read status register.
#define	AHT20_CMD_INIT   0xBE
	Command byte: initialise / calibrate the sensor.
#define	AHT20_CMD_TRIGGER   0xAC
	Command byte: trigger a humidity + temperature measurement.

Typedefs
typedef int8_t(*	AHT20_I2C_Read_Func) (uint8_t dev_addr, uint8_t reg_addr, uint8_t *data, uint16_t len)
	Function pointer type for platform I2C read operations.
typedef int8_t(*	AHT20_I2C_Write_Func) (uint8_t dev_addr, uint8_t reg_addr, uint8_t *data, uint16_t len)
	Function pointer type for platform I2C write operations.
typedef void(*	AHT20_Delay_Func) (uint32_t ms)
	Function pointer type for platform millisecond delay.

Functions
int8_t	AHT20_Init (AHT20_HandleTypeDef *dev)
	Initialises the AHT20 sensor.
int8_t	AHT20_Read (AHT20_HandleTypeDef *dev)
	Triggers a measurement and reads humidity and temperature from the AHT20.

Detailed Description

Driver interface for the AHT20 humidity and temperature sensor.

The AHT20 communicates over I2C at a fixed address of 0x38. The driver is platform-independent: the caller injects the I2C read/write and delay function pointers at initialisation time, so the same code runs on any MCU that provides those three primitives.

Typical usage:

AHT20_HandleTypeDef haht20;
haht20.i2c_read  = my_i2c_read;
haht20.i2c_write = my_i2c_write;
haht20.delay_ms  = my_delay;
AHT20_Init(&haht20);
 
AHT20_Read(&haht20);
float rh   = haht20.humidity;     // % RH
float degC = haht20.temperature;  // °C

Author

Şule Nur Demirdaş

Date

April 2026

Typedef Documentation

AHT20_Delay_Func

typedef void(* AHT20_Delay_Func) (uint32_t ms)

Function pointer type for platform millisecond delay.

Parameters

ms	Delay in milliseconds.

AHT20_I2C_Read_Func

typedef int8_t(* AHT20_I2C_Read_Func) (uint8_t dev_addr, uint8_t reg_addr, uint8_t *data, uint16_t len)

Function pointer type for platform I2C read operations.

Parameters

dev_addr	8-bit device address (HAL left-shifted format).
reg_addr	Register address; 0 for raw master-receive.
data	Buffer to store received bytes.
len	Number of bytes to read.

Returns

0 on success, non-zero on error.

AHT20_I2C_Write_Func

typedef int8_t(* AHT20_I2C_Write_Func) (uint8_t dev_addr, uint8_t reg_addr, uint8_t *data, uint16_t len)

Function pointer type for platform I2C write operations.

Parameters

dev_addr	8-bit device address (HAL left-shifted format).
reg_addr	Register address; 0 for raw master-transmit.
data	Buffer containing bytes to send.
len	Number of bytes to write.

Returns

0 on success, non-zero on error.

Function Documentation

AHT20_Init()

int8_t AHT20_Init

(

AHT20_HandleTypeDef *

dev

)

Initialises the AHT20 sensor.

Sends a status request and, if the calibration bit is not set, issues the initialisation command. Requires a 40 ms power-on delay before calling.

Parameters

[in,out]

dev

Pointer to an AHT20_HandleTypeDef with function pointers set.

Returns

0 on success.

-1 if any function pointer is NULL.

-2 if the status write fails.

-3 if the status read fails.

-4 if the initialisation command write fails.

AHT20_Read()

int8_t AHT20_Read

(

AHT20_HandleTypeDef *

dev

)

Triggers a measurement and reads humidity and temperature from the AHT20.

Sends the trigger command, waits 80 ms for conversion, reads 7 bytes, and converts the raw 20-bit values to physical units stored in dev->humidity and dev->temperature. The CRC byte (rx_buffer[6]) is currently not verified.

Parameters

[in,out]

dev

Pointer to an initialised AHT20_HandleTypeDef.

Returns

0 on success.

-1 if any function pointer is NULL.

-2 if the trigger command write fails.

-3 if the data read fails.

-4 if the busy flag in the status byte is set.