STM32 IIC protocol controls pca9685 steering gear drive board

         This tutorial is different from most online tutorials , Focus on how to use programming PCA9685, Instead of focusing on the principles , In the end, you are still confused . This is an article to teach you how to output a fixed steering angle , How to migrate programs , from PCA9685 The principle to how to transplant the tutorial , Learn theory in your hands .

Single chip model ：stm32f103c8t6

Use stm32 It is not difficult to control a steering gear , But if you control more than one steering gear , Then the hardware resources are stretched .

therefore , Must use artifact ,PCA9685 了 , I believe you can take the initiative to search the Internet PCA9685, I must know PCA9685 It's so awesome , I won't retell it .

Old rules , Submit the source code to , Get the source code first , Listen to me again .

Pay attention to WeChat public number “ Guangyi electronics ”(dlrcclub), reply PCA9685 You can get the network disk link .

We start from the whole keil Take a look at the project ：

         All we need to pay attention to is two files , One is IIC Driver file , One is PCA9685 The driver file for , For transplantation , Just take these two .C Documents and corresponding .h Put the file in your project directory , You can complete the function call , It's that simple ？  Yes , It's that simple . Let's take a closer look at PCA9685 Driving function of , And explain PCA9685 Function functions .

void pca_setfreq(float freq)// Set up PWM frequency 
{
		u8 prescale,oldmode,newmode;
		double prescaleval;
		freq *= 0.92; 
		prescaleval = 25000000;
		prescaleval /= 4096;
		prescaleval /= freq;
		prescaleval -= 1;
		prescale =floor(prescaleval + 0.5f);

		oldmode = pca_read(pca_mode1);
	
		newmode = (oldmode&0x7F) | 0x10; // sleep
	
		pca_write(pca_mode1, newmode); // go to sleep
	
		pca_write(pca_pre, prescale); // set the prescaler
	
		pca_write(pca_mode1, oldmode);
		delay_ms(2);
	
		pca_write(pca_mode1, oldmode | 0xa1); 
}

         We all know that the steering gear is 20ms A periodic pulse produces a 0.5-2.5ms Controlled by a pulse of ,PCA9685 It is necessary to set the steering gear control frequency manually during driving , This function on the graph is used , Please refer to the manual for the specific principle of this function , These principles are not covered here , You just use this function directly , That's all right. .

         We set the frequency , Also configure the duty cycle , In this way, the steering gear can be controlled according to different angles ,LED0_ON_L、LED0_ON_H、LED0_OFF_L、LED0_OFF_H+4 These are PCA9685 Of IIC Address , Because we only use this module here , So take the first address , Look down again ,num、on and off Variable ,num Is the channel number of the module , For example, control. 0 Channel number one , control 1 Channel number one ,2 Channel number, etc , It depends on how many steering gears are connected to your module , And which steering gear you want to use ,on and off These two variables are used to configure the duty cycle .

        on：pwm Rising count value 0-4096;off：pwm Drop count 0-4096, One pwm The cycle is divided into 4096 Share .

         from 0 Start +1 Count , Count on Time hopping goes high , Continue counting to off when , Jump to low level , Until the meter is full 4096 restart . So when on It's not equal to 0 when , Can be used as a delay , When on be equal to 0 when ,0ff/4096 Value , Namely pwm Duty cycle of .

         Finally, let's look at the servo channel and the angle control function , And how some parameters in the function are calculated .

void Servo_angle(u8 num,u8 angle)
{
	u32 off = 0;
  off = (u32)(158+angle*2.2);
	pca_setpwm(num,0,off);
}

          The main function of this function is to control the channel number and steering gear rotation angle , One of them off = （u32）（158+angle*2.2） Many students can't understand ,158 and 2.2 How did you get it ？

Here we give an example ：

To turn to 60 For example ：

60 Pulse width corresponding to degrees = 0.5ms+（60/180）*2（2.5ms-0.5ms） = 1.1666ms

Convert to duty cycle = 1.1666ms / 20ms = off /4096,off = 239,50hz The corresponding period is 20ms.

setPWM(num,0,239);

When you see this, you should understand 158 How did you calculate it , Refer to the above 239, You can figure it out 158 Corresponding duty cycle .

PS:0° The corresponding value is about 130,180° The corresponding value is 530, The maximum is 590.

158+angle *2.2 = 360.

In this way, we can define the output channel and angle of the steering gear according to our own ideas .

One of the projects is doc file , Some difficulties in the program are explained and calculated , I hope that helps .