Preface ： This article is HAL library Under the SG90 The steering gear experiment , The use of steering gear is very common . How it works （PWM Adjust the ） And programming is also very simple . As the front wheel control of smart car , Direction control of unmanned ship, etc , Can't leave the figure of the steering gear , I hope you can master this simple module .（ The experimental code is at the end of the article ）

         Experimental hardware ：STM32F103C8T6;SG90 The steering gear

         Hardware physical drawing ：

           design sketch ：

  Pin connection ：

VCC --> 5V

GND --> GND

PWM（ The signal line ） --> PA0

One 、SG90 Introduction to steering gear module  

          Steering gear is a kind of position （ angle ） servo Of Driver , It is suitable for those control systems that need to change and maintain the angle . In high-end remote control toys , Such as The plane 、 Submarine model , Remote control robot Has been widely used .

        “ servo ”— The word comes from Greek “ slave ” It means . People want to “ Servo mechanism ” Be a handy taming tool , Act in compliance with control signals . Before the signal arrives , The rotor is stationary ; When the signal comes , The rotor turns immediately ; When the signal disappears , The rotor can stop immediately . Because of its “ servo ” performance , Hence the name —— servo system .

Classification of steering gear ： 

         Simulate the steering gear ： need Ceaselessly send out Destination PWM The signal , To rotate to the specified position . for example ： I now let it spin 90 degree , I need to keep sending 90 Degree PWM The signal cannot stop until it reaches the specified position .（ What we use SG90 It's a simulated steering gear ）
         Digital steering gear ： Just give A destination PWM The signal , You can rotate to the specified position . for example ： I now let it spin 90 degree , I only need to send it once 90 Degree PWM The signal , It can be rotated to 90 degree .

PWM The signal ：PWM, English name Pulse Width Modulation, Short for pulse width modulation , It is by modulating the width of a series of pulses , Equivalent to the required waveform （ Including shape and amplitude ）, Digitally code the analog signal level , That is to say, adjust the signal by adjusting the change of duty cycle 、 Changes in energy, etc , Duty cycle means in a cycle , The time when the signal is at high level accounts for the percentage of the whole signal period , For example, the duty cycle of square wave is 50%.

appearance ：

Physical wiring ：

Two 、 How the steering gear works

         The control of steering gear generally requires One 20ms about （50Hz） Time base pulse , The high level part of the pulse is generally 0.5ms-2.5ms Angle control pulse part in range , The total interval is 2ms. With 180 For example, angle servo , So the corresponding control relationship is ：

 Relationship between angle and pulse time 
##############################################################
    0.5MS    1.0MS    1.5MS    2.0MS    2.5MS
     0°       45°      90°      135°     180°
##############################################################

  Particular attention ： On the market 180° The steering gear and 360° The steering gear , There's a difference between the two , Readers need to pay attention when buying .

180° Steering gear version ： You can control the rotation angle 、 Angular positioning . After power on, the steering gear will automatically reset to 0°, Its angle is controlled by pulse signal with certain parameters .

360° Steering gear version ： Uncontrollable angle , Only rotate clockwise 、 Counter clockwise rotation 、 stop it 、 Adjust speed . No angle positioning , Power on will not reset to 0°. Because this is 360° Arbitrarily rotating , No, 0. Its selection is controlled by pulse signals with certain parameters .

        Programming ideas ： When readers control the steering gear , Just use a timer to generate PWM Adjust the . use PWM Adjust the corresponding ms The number of pulses can realize the fixed angle control of the steering gear .

3、 ... and 、CubexMX To configure

1、RCC Configure external high-speed crystal oscillator （ Higher accuracy ）——HSE;

2、SYS To configure ：Debug Set to Serial Wire（ Otherwise, the chip may lock itself ）;

 3、TIM2 To configure ： Use TIM2 Of Channel1 produce PWM The signal （ control SG90）;

Meaning of data parameters ：

         At this point PWM Waveform frequency ：72M / (719 +1)/ (1999+1) = 50Hz

        Timer cycle ：1/50 = 20ms

4、 Clock tree configuration ：

5、 Engineering configuration

  Four 、 Code

main function :

int main(void)
{
  /* USER CODE BEGIN 1 */
 
  /* USER CODE END 1 */
 
  /* MCU Configuration--------------------------------------------------------*/
 
  /* Reset of all peripherals, Initializes the Flash interface and the Systick. */
  HAL_Init();
 
  /* USER CODE BEGIN Init */
 
  /* USER CODE END Init */
 
  /* Configure the system clock */
  SystemClock_Config();
 
  /* USER CODE BEGIN SysInit */
 
  /* USER CODE END SysInit */
 
  /* Initialize all configured peripherals */
  MX_GPIO_Init();
  MX_TIM2_Init();
  /* USER CODE BEGIN 2 */
  HAL_TIM_PWM_Start(&htim2,TIM_CHANNEL_1);//*** Timer 2 initialization 
  /* USER CODE END 2 */
 
  /* Infinite loop */
  /* USER CODE BEGIN WHILE */
  while (1)
  { 
      int i=1000; // Cycle interval 1s
      
      //* The steering gear points 0°
      __HAL_TIM_SET_COMPARE(&htim2,TIM_CHANNEL_1,50); // Equivalent to one cycle （20ms） Yes 0.5ms High pulse 
      HAL_Delay(i);
      //* The steering gear points 180°
      __HAL_TIM_SET_COMPARE(&htim2,TIM_CHANNEL_1,250); // Equivalent to one cycle （20ms） Yes 2.5ms High pulse 
      HAL_Delay(i);
 
    /* USER CODE END WHILE */
 
    /* USER CODE BEGIN 3 */
  }
  /* USER CODE END 3 */
}

matters needing attention ：

        Simulate the steering gear SG90 The use of is to make use of PWM To control the angle pointed by the steering gear .

         By modifying the handle __HAL_TIM_SET_COMPARE(&htim2,TIM_CHANNEL_1,value) In the parameters of the value It can control the angle of the steering gear .

Here we use SG90 Take the steering gear as an example to explain ：

        It is known that 0.5ms Point to 0° Location ,2.5ms Point to 180° Location .

        For example, you need to point to m° It's about :

        2.5-0.5=2ms  -->  Corresponding to 180°

        value/(1999+1)*20=0.5+（m/180）× 2

5、 ... and 、 Experimental results

6、 ... and 、 Code

link ：https://pan.baidu.com/s/1lphofKe9yepXJ5XPwHkdUQ Extraction code ：3doi