filter.h File Reference

Sliding-window median filter for floating-point sensor values. More...

#include "stdint.h"

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Data Structures
struct	Filter_Handle_t
	Internal state of one sliding-window median filter instance. More...

Macros
#define	MAX_WINDOW_SIZE   20
	Maximum number of samples the filter window can hold.

Functions
float	filter_sensor_value (Filter_Handle_t *p_filt, float raw_sensor_value, uint8_t window_size)
	Applies a sliding-window median filter to a single raw sample.
float	calculate_median (float *array, uint8_t array_size)
	Computes the median of a pre-sorted float array.
void	bubble_sort (float *array, uint8_t array_size)
	Sorts a float array in ascending order using bubble sort.

Detailed Description

Sliding-window median filter for floating-point sensor values.

The filter maintains a fixed-size window of the most recent raw readings. Each call to filter_sensor_value() appends the new sample to the window (evicting the oldest one when full), sorts a copy of the window, and returns the median. This effectively suppresses impulse noise while preserving step changes faster than a moving-average filter of the same length.

Utility functions bubble_sort() and calculate_median() are also exposed so that calculate_statistics() in main.c can reuse them on the ring buffer.

Author

Şule Nur Demirdaş

Date

April 2026

Function Documentation

bubble_sort()

void bubble_sort	(	float *	array,
		uint8_t	array_size )

Sorts a float array in ascending order using bubble sort.

Runs in O(n²) time; suitable for the small window sizes used here (≤ MAX_WINDOW_SIZE = 20 elements).

Parameters

[in,out]	array	Pointer to the array to sort in place.
[in]	array_size	Number of elements in array.

calculate_median()

float calculate_median	(	float *	array,
		uint8_t	array_size )

Computes the median of a pre-sorted float array.

For even-length arrays the median is the average of the two central elements. For odd-length arrays it is the single central element.

Parameters

[in]	array	Pointer to a sorted array of floats.
[in]	array_size	Number of elements in array.

Returns

Median value.

filter_sensor_value()

float filter_sensor_value	(	Filter_Handle_t *	p_filt,
		float	raw_sensor_value,
		uint8_t	window_size )

Applies a sliding-window median filter to a single raw sample.

On each call the new sample is inserted into the window. If the window has not yet reached window_size the sample is appended; otherwise the oldest sample is discarded (left-shift) and the new one placed at the end. A copy of the window is then sorted and the median returned.

Parameters

[in,out]	p_filt	Pointer to the filter state structure.
[in]	raw_sensor_value	The latest raw measurement from the sensor.
[in]	window_size	Effective window length (must be ≤ MAX_WINDOW_SIZE).

Returns

Filtered (median) value of the current window contents.