Line data    Source code

       1              : /**
       2              :  * @file
       3              :  * @brief Low-pass filter implementation
       4              :  *
       5              :  * This module provides a low-pass filter implementation for smoothing sensor readings
       6              :  * and reducing noise in analog signals. The filter uses an exponential moving average
       7              :  * algorithm with configurable response time.
       8              :  */
       9              : 
      10              : #ifndef ROCKETLIB_LOW_PASS_FILTER_H
      11              : #define ROCKETLIB_LOW_PASS_FILTER_H
      12              : 
      13              : #include <stdbool.h>
      14              : #include <stdint.h>
      15              : 
      16              : #include "common.h"
      17              : 
      18              : #ifdef __cplusplus
      19              : extern "C" {
      20              : #endif
      21              : 
      22              : /**
      23              :  * @brief Calculate the sample frequency based on the time difference in milliseconds
      24              :  *
      25              :  * @param time_diff_ms Time difference between samples in milliseconds
      26              :  * @return double Sample frequency in Hz
      27              :  */
      28              : static inline double sample_freq(double time_diff_ms) {
      29            1 :         return 1000.0 / time_diff_ms;
      30              : }
      31              : 
      32              : /**
      33              :  * @brief Calculate the alpha value for the low-pass filter based on the response time
      34              :  *
      35              :  * The alpha value determines the filter's responsiveness. A higher alpha value results
      36              :  * in faster response but less filtering, while a lower alpha value provides more filtering
      37              :  * but slower response.
      38              :  *
      39              :  * @param TR Response time constant in milliseconds
      40              :  * @param time_diff_ms Time difference between samples in milliseconds
      41              :  * @return double Alpha value (0.0 to 1.0) for the low-pass filter
      42              :  */
      43              : static inline double low_pass_alpha(double TR, double time_diff_ms) {
      44              :         double freq = sample_freq(time_diff_ms);
      45            1 :         return (freq * TR / 5.0) / (1.0 + freq * TR / 5.0);
      46              : }
      47              : 
      48              : /**
      49              :  * @brief Initializes the low-pass filter by calculating and storing the alpha value
      50              :  *
      51              :  * This function calculates the alpha value based on the given response time and stores
      52              :  * it in the provided pointer. The alpha value is used in subsequent filter updates.
      53              :  *
      54              :  * @param alpha Pointer to store the calculated alpha value
      55              :  * @param response_time Response time constant in milliseconds (must be > 0)
      56              :  * @return w_status_t Returns W_SUCCESS on success, W_INVALID_PARAM if alpha is NULL or
      57              :  * response_time is invalid
      58              :  */
      59              : w_status_t low_pass_filter_init(double *alpha, double response_time);
      60              : 
      61              : /**
      62              :  * @brief Updates the low-pass filter with a new value and returns the operation status
      63              :  *
      64              :  * This function applies the low-pass filter algorithm to the new input value using the
      65              :  * provided alpha value. The filtered result is stored in low_pass_value and updated
      66              :  * in-place for the next iteration.
      67              :  *
      68              :  * @param alpha Alpha value (0.0 to 1.0) for the low-pass filter
      69              :  * @param new_input_value New input value to filter
      70              :  * @param low_pass_value Pointer to the current filtered value (updated in-place)
      71              :  * @return w_status_t Returns W_SUCCESS on success, W_INVALID_PARAM if low_pass_value is
      72              :  * NULL or alpha is out of valid range (0.0 to 1.0)
      73              :  */
      74              : w_status_t update_low_pass(double alpha, uint16_t new_input_value, double *low_pass_value);
      75              : 
      76              : #ifdef __cplusplus
      77              : }
      78              : #endif
      79              : 
      80              : #endif /* ROCKETLIB_LOW_PASS_FILTER_H */