Main program body for the STM32F4 multi-sensor data acquisition system. More...

#include "main.h"
#include "i2c_core.h"

Macros
#define	RING_BUFFER_SIZE 30
	Number of samples held in each ring buffer (equals the reporting period in seconds).

Functions
void	SystemClock_Config (void)
	System Clock Configuration.
int8_t	stm32_i2c_read_wrapper (uint8_t dev_addr, uint8_t reg_addr, uint8_t *data, uint16_t len)
	Platform I2C read wrapper for sensor drivers.
int8_t	stm32_i2c_write_wrapper (uint8_t dev_addr, uint8_t reg_addr, uint8_t *data, uint16_t len)
	Platform I2C write wrapper for sensor drivers.
void	stm32_delay_wrapper (uint32_t ms)
	Platform delay wrapper for sensor drivers.
int	main (void)
	The application entry point.
void	HAL_TIM_PeriodElapsedCallback (TIM_HandleTypeDef *htim)
	TIM3 period-elapsed callback — fires every 1 second.
void	calculate_statistics (buf_handle_t p_handle, Sensor_Stats_t stats)
	Computes descriptive statistics from a ring buffer.
void	Error_Handler (void)
	This function is executed in case of error occurrence.

Variables
I2C_HandleTypeDef	hi2c3
TIM_HandleTypeDef	htim3
UART_HandleTypeDef	huart2
BMP180_HandleTypeDef	hbmp180
BH1750_HandleTypeDef	hbh1750
AHT20_HandleTypeDef	haht20
Filter_Handle_t	hFiltHum
Filter_Handle_t	hFiltTemp
Filter_Handle_t	hFiltLight
buf_handle_t	hBufHum
buf_handle_t	hBufTemp
buf_handle_t	hBufLight
Sensor_Stats_t	hum_stats
Sensor_Stats_t	temp_stats
Sensor_Stats_t	light_stats
volatile uint8_t	read_sensor_flag = 0

Detailed Description

Main program body for the STM32F4 multi-sensor data acquisition system.

This application reads humidity and temperature data from an AHT20 sensor, illuminance from a BH1750 sensor, and atmospheric pressure from a BMP180 sensor over I2C. Raw readings are filtered with a sliding-window median filter and stored in separate circular (ring) buffers. Every 30 seconds the system computes min, max, median and standard deviation for each sensor and transmits the results over USART2 at 115200 baud in the following format:

HUM:<min>,<max>,<median>,<std_dev>\r\n
TMP:<min>,<max>,<median>,<std_dev>\r\n
LUX:<min>,<max>,<median>,<std_dev>\r\n

A 1-second tick is generated by TIM3 configured on the APB1 bus (prescaler = 12499, period = 999, resulting in a 1 Hz interrupt at 12.5 MHz).

Author: Şule Nur Demirdaş

Date: April 2026

Attention: Copyright (c) 2026 STMicroelectronics. All rights reserved. This software is licensed under terms found in the LICENSE file in the root directory of this software component.

Function Documentation

◆ calculate_statistics()

void calculate_statistics	(	buf_handle_t *	p_handle,
		Sensor_Stats_t *	stats )

Computes descriptive statistics from a ring buffer.

Computes min, max, median, and standard deviation from a ring buffer.

Iterates over all valid samples in p_handle to find the minimum, maximum and arithmetic mean. A second pass computes the population standard deviation. The buffer is then copied to a temporary array, sorted with bubble_sort(), and the median is extracted.

Note: The function returns immediately if the buffer is empty.

Parameters

[in]	p_handle	Pointer to the ring buffer handle containing the samples.
[out]	stats	Pointer to the Sensor_Stats_t structure to populate.

◆ Error_Handler()

void Error_Handler ( void )

This function is executed in case of error occurrence.

Return values

None

◆ HAL_TIM_PeriodElapsedCallback()

void HAL_TIM_PeriodElapsedCallback ( TIM_HandleTypeDef * htim )

TIM3 period-elapsed callback — fires every 1 second.

Sets read_sensor_flag to notify the main loop that a new sample should be acquired, and toggles the green LED as a heartbeat indicator.

Parameters

[in] htim Pointer to the TIM_HandleTypeDef that triggered the callback.

◆ main()

int main ( void )

The application entry point.

Return values

int

◆ stm32_delay_wrapper()

void stm32_delay_wrapper ( uint32_t ms )

Platform delay wrapper for sensor drivers.

Parameters

[in] ms Delay duration in milliseconds.

◆ stm32_i2c_read_wrapper()

int8_t stm32_i2c_read_wrapper	(	uint8_t	dev_addr,
		uint8_t	reg_addr,
		uint8_t *	data,
		uint16_t	len )

Platform I2C read wrapper for sensor drivers.

Sensor drivers call this function pointer instead of HAL directly, keeping the drivers portable across different MCU platforms.

When reg_addr is 0 the function performs a raw master-receive (no register address phase). Otherwise it uses HAL_I2C_Mem_Read.

Parameters

[in]	dev_addr	8-bit I2C device address (already left-shifted by 1).
[in]	reg_addr	Register address to read from; 0 for raw receive.
[out]	data	Pointer to the buffer that receives the data.
[in]	len	Number of bytes to read.

Returns: 0 on success, -1 on I2C error.

◆ stm32_i2c_write_wrapper()

int8_t stm32_i2c_write_wrapper	(	uint8_t	dev_addr,
		uint8_t	reg_addr,
		uint8_t *	data,
		uint16_t	len )

Platform I2C write wrapper for sensor drivers.

When reg_addr is 0 the function performs a raw master-transmit (no register address phase). Otherwise it uses HAL_I2C_Mem_Write.

Parameters

[in]	dev_addr	8-bit I2C device address (already left-shifted by 1).
[in]	reg_addr	Register address to write to; 0 for raw transmit.
[in]	data	Pointer to the data to transmit.
[in]	len	Number of bytes to write.