stm32+pca9685 control servo mechanical arm

1. Hardware

PCA9685 is a chip with 12-bit precision and 16-channel PWM wave output based on IIC bus communication. When the chip was first launched by NXP, it was mainly used for LED switch dimming. However, judging from the current domestic situation, it seems to be more widely used by Arduino in the field of steering gear control. 
 
Since this module is mainly active around Aruino, it is very perfect to develop its underlying driver library using Arduino, but it is not very friendly to microcontroller developers. They need to write the underlying driver on the microcontroller according to the user manual. 
 
The allocation of its address is determined by the short-circuit pad on the upper right of the module. From A0-A5, it represents the lowest bit to the highest bit of the address, that is, up to 2^5=32 modules can be cascaded, and the address is: 1+A5+A4+A3+A2+A1+A0+rw. If no short circuit is needed, Ax=0; if short circuit is done, Ax=1; if rw is for writing, rw=0; if rw is for reading, rw=1; so if writing data without short circuit, the address should be 1000 0000 =0x80. Many people, including Taobao merchants, mistakenly believe that the default address is 0x40, which is a rip-off. 

2.IIC communication

SCL is connected to PH4, SDA is connected to PH5, VCC is connected to 3.3V, GND is connected, and V+ is simply for power supply. It is not connected when driving a high-power servo. However, the two ports of the external power supply must be connected to the positive and negative poles, otherwise it cannot supply power.

3. Procedure

First, we need the underlying driver file for IIC communication and the driver file for pca9685. The driver for pca9685 can be modified based on the driver file for pcf8574. The key lies in the following two functions:

void setPWM(u8 num, u16 on, u16 off) 

void setPWMFreq(u8 freq)

Note that u8 is used instead of unsigned int. 

There is one thing to note:

IIC_Send_Byte(PCA9685_adrr|0X01); //Send device address + read command

This is the r/w mentioned above. Since this is the read address, it must be 0X01. 

In the main function:

PCA9685_write(PCA9685_MODE1,0x0);

    setPWMFreq(50); 

setPWM(0, 0, 220);

            delay_ms(2000);

            setPWM(2, 0,110);

            delay_ms(2000);

            setPWM(1, 0,130);

            delay_ms(2000);

            setPWM(1, 0,150);

            delay_ms(2000);

            setPWM(1, 0,175);

            delay_ms(2000);

            setPWM(1, 0,195);

            delay_ms(2000);

For 180-degree servos, the only way to prevent excessive impact caused by excessive speed is to use delay and angle subdivision.