servo-pwm.c
The timer configured to count microseconds generates the servo control pulse (0.5 to 2.5 ms over a 20 ms period). servo_angle converts any angle into a compare value: the basis of any robot arm in C.
Hardware
A Blue Pill STM32F103C8T6 (Cortex-M3 @ 72 MHz, 64 KB flash) powered by micro-USB or external 3.3 V; programmed over SWD or the serial bootloader. 1 hobby servo (SG90/MG90S) + external 5 V supply advised.
Wiring
Servo signal on the channel pin (e.g. PA6 for TIM3_CH1, set in the .ioc), + to external 5 V, grounds tied together.
How it works
The timer counts at 1 MHz (PSC set in CubeMX) with ARR=19999, i.e. 20 ms; the compare value sets the pulse width. The loop sweeps 0-180° in 5° steps.
Running it
STM32CubeIDE project (STM32F103C8) or Arduino (STM32 core): program over SWD (ST-LINK, DAPLink adapter) or the serial bootloader (BOOT0 to 1). Note: PC13 LED is active LOW.
Variants
Add smoothing (position interpolation), or drive 4 servos on 4 channels of one timer for a mini robot arm.
servo-pwm.c
// Servo 50 Hz : periode 20 ms, impulsion 0,5..2,5 ms.
// Timer configure dans CubeMX : PSC et ARR pour compter en us.
#include "main.h"
extern TIM_HandleTypeDef htim3; // ex. 1 MHz de comptage, ARR=19999
#define SERVO_CANAL TIM_CHANNEL_1
static void servo_angle(int angle) { // 0..180
uint32_t us = 500 + (uint32_t)angle * 2000 / 180; // 500..2500 us
__HAL_TIM_SET_COMPARE(&htim3, SERVO_CANAL, us);
}
uint32_t t0 = 0;
int angle = 0, sens = 1;
int main(void) {
HAL_Init();
SystemClock_Config();
MX_GPIO_Init();
MX_TIM3_Init();
HAL_TIM_PWM_Start(&htim3, SERVO_CANAL);
for (;;) {
if (HAL_GetTick() - t0 >= 20) { // pas de 20 ms
t0 = HAL_GetTick();
servo_angle(angle);
angle += sens * 5; // 5 degres par pas
if (angle >= 180) sens = -1;
if (angle <= 0) sens = 1;
}
}
}