Steering gear control (stm32f103c8t6)

Preface

        This article is based on STM32F103C8T6 As the main control chip , adopt PB6 Port output PWM, Achieve control 180° The steering gear .

One 、 Steering control principle

（ One ） summary

        The steering gear is a position servo driver , It is a small device with an output shaft . When we send a control signal to the server , The output shaft can be turned to a specific position . Only when the control signal remains constant , The servo mechanism will keep the relative angular position unchanged . If the control signal changes , The position of the output shaft will change accordingly . The control of the steering gear is mostly through PWM Signal controlled .

        notes ： The steering gear is divided into 90°、180°、270°、360° The steering gear , among 360° The steering gear can only control the rotation speed and cannot be fixed at a certain angle .

（ Two ）PWM

        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 the signal is at the high level as a percentage of the entire signal cycle . Here's the picture

（ 3、 ... and ） Control principle

        Through the signal line to the steering gear PWM The signal controls the output of the steering gear , Generally speaking ,PWM The cycle and duty cycle of , Programmable .

        When we send a pulse width of 1.5ms when , The output shaft of the steering gear will move to the middle position 0°;

        When the pulse width is 1ms when , The output shaft of the steering gear will move to the middle position -45°;

         The pulse width is 2ms when , The output shaft of the steering gear will move to the middle position 45°.

        notes ： The angle between the maximum position and the minimum position may be different between different types and brands of servo motors . Many servers only rotate about 170 degree （ Or just 90 degree ）, But the width is 1.5 ms The servo pulse will usually set the servo to the middle position （ It's usually half of the specified full range ）; Refer to the following figure for details.

Duty cycle = t / T The relevant parameters are as follows ：

t = 0.5ms —————— The rudder will turn to -90 °
t = 1.0ms —————— The rudder will turn to -45°
t = 1.5ms —————— The rudder will turn to 0°
t = 2.0ms —————— The rudder will turn to 45°
t = 2.5ms —————— The rudder will turn to 90°

 PWM The period is 20ms = （2000*720）/72000000 = 0.2, Programmed TIM_Period = 719,TIM_Prescaler = 1999（ In this paper, the program ）

Two 、 Hardware connection

（ One ） Description of steering gear line

（ Two ） Pin connection

master control	The steering gear
5V	+5V
GND	GND
PB6	PWM

 

3、 ... and 、 Reference code

1、 initialization

void TIM4_CH1_PWM_Init(u16 arr,u16 psc)
{
	GPIO_InitTypeDef GPIO_InitStruct;
	TIM_TimeBaseInitTypeDef TIM_TimeBaseStruct;
	TIM_OCInitTypeDef TIM_OCInitTypeStruct;
	
	RCC_APB1PeriphClockCmd(RCC_APB1Periph_TIM4,ENABLE);
	
	// Only when the multiplexing function is enabled can the clock be remapped 
	RCC_APB2PeriphClockCmd(RCC_APB2Periph_GPIOB  ,ENABLE); 
	
	//TIM3 Partial remapping 
	/*
	* Check the data book , The timer channel of the pin is fully mapped , Or partial mapping 
	* The two call parameters are different 
	* Complete mapping  ：GPIO_FullRemap_TIM4
	* Partial mapping  ：GPIO_PartialRemap_TIM4
	*/
	
	// Set this pin to multiplex output function 
	GPIO_InitStruct.GPIO_Mode = GPIO_Mode_AF_PP;
	GPIO_InitStruct.GPIO_Pin = GPIO_Pin_6;
	GPIO_InitStruct.GPIO_Speed = GPIO_Speed_50MHz;
	GPIO_Init(GPIOB,&GPIO_InitStruct);
	
	// initialization TIM4
	TIM_TimeBaseStruct.TIM_Period = arr;// Reload value  
	TIM_TimeBaseStruct.TIM_Prescaler = psc;// Prescaled value  
	TIM_TimeBaseStruct.TIM_ClockDivision = 0; // The clock frequency division 1、2、4 frequency division 	
	TIM_TimeBaseStruct.TIM_CounterMode = TIM_CounterMode_Up;// Set counting mode 
	TIM_TimeBaseInit(TIM4,&TIM_TimeBaseStruct);
	
	// Initialize the output comparison parameters 
	TIM_OCInitTypeStruct.TIM_OCMode = TIM_OCMode_PWM2; // Select timer mode 
	TIM_OCInitTypeStruct.TIM_OutputState = TIM_OutputState_Enable;// Compare output enable 
	TIM_OCInitTypeStruct.TIM_OCPolarity = TIM_OCPolarity_High;// Output polarity 
	TIM_OC1Init(TIM4,&TIM_OCInitTypeStruct); // Select timer output channel  TIM4_CH1
	
	// Enable preload register 
	TIM_OC1PreloadConfig(TIM4,TIM_OCPreload_Enable);
	
	// Enable timer 
	TIM_Cmd(TIM4,ENABLE);
}

2、 The main function

int main(void)
{
	TIM4_CH1_PWM_Init(1999,719);//PWM frequency =72000000/（719+1）/（1999+1）=50hz=20ms
	
	while(1)
	{
		//-90 degree 
		TIM_SetCompare1(TIM4,1750);// Duty cycle （2000-1750）/2000*20ms=2.5ms

		//45 degree 
		//TIM_SetCompare1(TIM4,1800);// Duty cycle （2000-1800）/2000*20ms=2ms

		//0 degree 
		//TIM_SetCompare1(TIM4,1850);// Duty cycle （2000-1850）/2000*20ms=1.5ms

		//-45 degree 
		//TIM_SetCompare1(TIM4,1900);// Duty cycle （2000-1900）/2000*20ms=1ms

		//-90 degree 
		//TIM_SetCompare1(TIM4,1945);// Duty cycle （2000-1945）/2000*20ms=0.5ms  	
	}
}

Related codes , If necessary, you can download it yourself （ It can only send control rotation through the string ）
Network disk link ：
link ：https://pan.baidu.com/s/1p-lAXJ4pS6-Tw3DFqxdQhQ 
Extraction code ：ml04
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