Hardware Compnoents

• STM32 microcontroller (e.g., STM32F4 series)
• DC motor
• Motor driver IC (e.g., L298N or DRV8833)
• Power supply

Software Configuration

The STM32's timer peripheral is used to generate a PWM signal. The timer's auto-reload register (ARR) defines the period, and the capture/compare register (CCR) sets the pulse width (duty cycle).

Implementation

Peripheral Initialization

Configure a GPIO pin for alternate function output, connected to a timer channel. Enitialize the timer in PWM mode.

#include "stm32f4xx.h"

// PWM parameters
#define PWM_FREQ_HZ 20000
#define PWM_PERIOD_TICKS 1000
#define INITIAL_PULSE_WIDTH 300

void ConfigureMotorPins(void) {
    GPIO_InitTypeDef gpio_init;
    RCC_AHB1PeriphClockCmd(RCC_AHB1Periph_GPIOA, ENABLE);

    gpio_init.GPIO_Pin = GPIO_Pin_6;
    gpio_init.GPIO_Mode = GPIO_Mode_AF;
    gpio_init.GPIO_OType = GPIO_OType_PP;
    gpio_init.GPIO_Speed = GPIO_Speed_50MHz;
    gpio_init.GPIO_PuPd = GPIO_PuPd_NOPULL;
    GPIO_Init(GPIOA, &gpio_init);

    GPIO_PinAFConfig(GPIOA, GPIO_PinSource6, GPIO_AF_TIM3);
}

void SetupPWMTimer(void) {
    TIM_TimeBaseInitTypeDef tim_base_init;
    TIM_OCInitTypeDef tim_oc_init;

    RCC_APB1PeriphClockCmd(RCC_APB1Periph_TIM3, ENABLE);

    tim_base_init.TIM_Period = PWM_PERIOD_TICKS - 1;
    tim_base_init.TIM_Prescaler = (SystemCoreClock / PWM_FREQ_HZ) - 1;
    tim_base_init.TIM_ClockDivision = TIM_CKD_DIV1;
    tim_base_init.TIM_CounterMode = TIM_CounterMode_Up;
    TIM_TimeBaseInit(TIM3, &tim_base_init);

    tim_oc_init.TIM_OCMode = TIM_OCMode_PWM1;
    tim_oc_init.TIM_OutputState = TIM_OutputState_Enable;
    tim_oc_init.TIM_Pulse = INITIAL_PULSE_WIDTH;
    tim_oc_init.TIM_OCPolarity = TIM_OCPolarity_High;
    TIM_OC1Init(TIM3, &tim_oc_init);

    TIM_Cmd(TIM3, ENABLE);
}

Adjusting Motor Speed

The motor speed is controlled by varying the duty cycle. This is done by updating the CCR value.

void SetMotorSpeed(uint16_t pulse_width) {
    TIM_SetCompare1(TIM3, pulse_width);
}

int main(void) {
    ConfigureMotorPins();
    SetupPWMTimer();

    while (1) {
        // Example: Ramp up speed
        for (uint16_t width = 100; width < PWM_PERIOD_TICKS; width += 50) {
            SetMotorSpeed(width);
            // Insert a small delay
            for (volatile int i = 0; i < 100000; i++);
        }
    }
}