Features of calculating computing time when designing digital filters on STM32F103 microcontrollers from STMicroelectronics Corporation

The article is devoted to the creation of a method for estimating the frequency range of signals when designinga digital filter (DF) by measuring the calculation time of the current reference in the system of a digital low-pass filter(LPF) with a finite impulse response (FIR) on the STM32F103C8T6 microcontroller.A setup for studying the filter has been developed, which includes: a generator of sinusoidal signals; an inputcircuit to ensure the supply of positive values to the ADC input; the STM23F103C8T6 microcontroller module itself,which processes the input signal in real time and implements the filtering function.The microcontroller timer is configured to generate interrupts for sampling the input signal with a samplingfrequency of 35.15 kHz. A program code has been created to ensure the minimum conversion time during the filteringprocess.A software implementation of the FIR low-pass filter with a cutoff frequency of 800 Hz has been performed. Theimplementation of a filter with an order from units to hundreds is provided. The amplitude-frequency characteristics(AFC) of low- and high-order filters have been analyzed. A method has been developed for determining the period ofexecution of the convolution calculation by the microcontroller, which is the basis of the filtering process. A timersetting code has been developed for measuring time and displaying the result on the display in real time.The simplest convolution calculation algorithm has been selected and implemented in the C++ programminglanguage. The results of measurements of the convolution calculation time by the STM32F10С8Т6 microcontroller havebeen obtained depending on different orders of the digital filter. The results can be used to determine the requiredperiod (frequency) of signal sampling. Accordingly, they allow us to estimate the maximum frequency range of thesignal that can be processed in real time by a digital filter of the selected order.