{"id":392,"date":"2021-09-09T05:08:11","date_gmt":"2021-09-09T05:08:11","guid":{"rendered":"https:\/\/blog.embeddedexpert.io\/?p=392"},"modified":"2021-09-09T05:08:15","modified_gmt":"2021-09-09T05:08:15","slug":"working-with-stm32-and-timers-part-4-servo-motor-control","status":"publish","type":"post","link":"https:\/\/blog.embeddedexpert.io\/?p=392","title":{"rendered":"Working with STM32 and Timers part 4: Servo Motor Control"},"content":{"rendered":"\n
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Servo motor<\/figcaption><\/figure><\/div>\n\n\n\n

In pervious PWM guide (here<\/a>), discussed how to use TIM2 of STM32F411 to generate 2 PWM signals to fade 2 LEDs. In this guide, we shall use PWM signal to control a servo motor (SG90<\/strong>).<\/p>\n\n\n\n

In this guide, we shall cover the following <\/p>\n\n\n\n

  • What is servo motor and how to control it<\/li>
  • Connection<\/li>
  • Code<\/li>
  • Demo<\/li><\/ul>\n\n\n\n

    1. What is servo motor and how to control it<\/h2>\n\n\n\n

    A\u00a0servomotor<\/strong>\u00a0is a\u00a0rotary actuator<\/a>\u00a0or\u00a0linear actuator<\/a>\u00a0that allows for precise control of angular or linear position, velocity and acceleration.[1]<\/a><\/sup>\u00a0It consists of a suitable motor coupled to a sensor for position feedback. It also requires a relatively sophisticated controller, often a dedicated module designed specifically for use with servomotors. (Wikipedia link<\/a>).<\/p>\n\n\n\n

    The servo motor used in our guide has three wires: red, brown and orange.<\/p>\n\n\n\n

    Wire color<\/td>Function<\/td><\/tr>
    Red<\/td>Vcc (4~6V)<\/td><\/tr>
    Brown<\/td>GND<\/td><\/tr>
    Orange<\/td>Signal<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n
    \"\"<\/figure>\n\n\n\n

    In order to control the angle of the servo motor, a PWM signal of frequency 50Hz (20mS period) needed to be applied to the signal pin on the servo motor. to determine the angle of the servo as following:<\/p>\n\n\n\n

    Angle <\/td>Duty Cycle (Period)<\/td><\/tr>
    0<\/td>5% (1mS)<\/td><\/tr>
    90<\/td>7.5% (1.5mS)<\/td><\/tr>
    180<\/td>10%(2mS)<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n
    \"\"<\/figure><\/div>\n\n\n\n

    Hence we need to configure the TIM2 to generate 50Hz PWM signal on PA0 pin<\/p>\n\n\n\n

    2. Connection:<\/h2>\n\n\n\n

    In this guide, we need the following<\/p>\n\n\n\n

    • STM32F411 Nucleo<\/li>
    • SG90 microservo<\/li>
    • Hock-up wires<\/li><\/ul>\n\n\n\n
      \"\"
      Connection<\/figcaption><\/figure><\/div>\n\n\n\n
      \"\"
      Actual connection<\/figcaption><\/figure><\/div>\n\n\n\n

      3. Code:<\/h2>\n\n\n\n
      #include "stm32f4xx.h"                  \/\/ Device header\nvoid GPIO_Init(void);\nvoid Timer2_init(void);\nvoid delay(int ms );\nvoid servo_write(uint8_t angle);\n\nint pos;\nint main(void)\n{\n\nGPIO_Init();\nTimer2_init();\nwhile(1)\n{\nfor (pos = 0; pos <= 180; pos += 1) { \/\/ goes from 0 degrees to 180 degrees\n    \/\/ in steps of 1 degree\n    servo_write(pos);              \/\/ tell servo to go to position in variable 'pos'\n    delay(15);                       \/\/ waits 15ms for the servo to reach the position\n  }\n  for (pos = 180; pos >= 0; pos -= 1) { \/\/ goes from 180 degrees to 0 degrees\n    servo_write(pos);              \/\/ tell servo to go to position in variable 'pos'\n    delay(15);                       \/\/ waits 15ms for the servo to reach the position\n  }\n\n}\n}\n\nvoid GPIO_Init(void)\n{\nRCC->AHB1ENR|=RCC_AHB1ENR_GPIOAEN;\nGPIOA->AFR[0]|=(1<<0);\nGPIOA->MODER|=(1<<1);\n\n}\nvoid  Timer2_init(void){\nRCC->APB1ENR|=RCC_APB1ENR_TIM2EN; \/\/enable clock access tto tim2\nTIM2->PSC=4; \/\/set prescaller to 4 (16000000Hz\/4=4000000Hz)\nTIM2->ARR=63999; \/\/set the maximum count value \nTIM2->CNT=0; \/\/seset the current count\nTIM2->CCMR1=(1<<5)|(1<<6); \/\/configure the pins as PWM\nTIM2->CCER|=0x1; \/\/enbale channel1 and channel2\nTIM2->CR1=1; \/\/enable timer\n}\n\n\nvoid delay(int ms)\n\n{\n\nint i;\n\nfor(; ms>0 ;ms--)\n\n{\n\nfor(i =0; i<3195;i++);\n\n}\n\n}\n\nlong map(long x, long in_min, long in_max, long out_min, long out_max)\n{\n  return (x - in_min) * (out_max - out_min) \/ (in_max - in_min) + out_min;\n}\n\n\nvoid servo_write(uint8_t angle)\n\t{\n\t\n\tif(angle<0){angle=0;}\n\tif(angle>180){angle=180;}\n\t\n\t\nTIM2->CCR1=map (angle,0,180,2500,7000);\n\t\n\t\n\t\n\t}<\/pre><\/div>\n\n\n\n
      4. Demo:<\/h2>\n\n\n\n