樹莓派之PCA9685驅動無刷電機

關於i2c驅動，這裡用的是wiringpi做進一步封裝，i2c驅動的函式如下：

#include int checki2cdevicei***ist(unsigned char devaddr);
bool writebyte(int fd, unsigned char regaddr, unsigned char data);
bool writebit(int fd, unsigned char regaddr, unsigned char bitnum, unsigned char data);
bool writebits(int fd, unsigned char regaddr, unsigned char bitstart, unsigned char length,
unsigned char data);
bool writebytes(int fd, unsigned char regaddr, unsigned char length, unsigned char * data);
bool writeword(int fd, unsigned char regaddr, unsigned short data);
bool writewords(int fd, unsigned char regaddr, unsigned char length, unsigned short* data);
unsigned char readbyte(int fd, unsigned char regaddr);
void readbytes(int fd, unsigned char regaddr, unsigned char length, unsigned char *data);
unsigned char readbit(int fd, unsigned char regaddr, unsigned char bitnum, unsigned char *data);
unsigned char readbits(int fd, unsigned char regaddr, unsigned char bitstart, unsigned char length,
unsigned char *data);

fd由fd = wiringpii2csetup(pca9685_address);

unsigned char regaddr, unsigned char data，就模組的暫存器和要讀寫的資料。

bool writebyte(int fd, unsigned char regaddr, unsigned char data) 
unsigned char readbyte(int fd, unsigned char regaddr)

內部由wiringpii2cwritereg8(fd, regaddr, data)， wiringpii2creadreg8(fd, regaddr)封裝。

bool pca9685init()  else 
pca9685_initsuccess = true;
resetpca9685();
return true;
}void resetpca9685()  else 
}void pca9685setpwmfreq(unsigned short freq) 
void pca9685setpwm(unsigned char channel, unsigned short value) 
writebyte(pca9685_fd, pca9685_led0_off_l + pca9685_led_shift * channel, value & 0xff);
writebyte(pca9685_fd, pca9685_led0_off_h + pca9685_led_shift * channel, value >> 8);
}

我設定的頻率為50hz，那該如何驅動無刷電機？ 50hz的頻率，週期為20ms，暫存器的值在0--4096之間。我手頭的無刷電調能接收的pwm方波高電平在，1.1ms--1.9ms之間。1.1ms是最低油門值，1.9是最大油門值。遙控器同樣也是輸出50hz，1.1ms--1.9ms的pwm波。先求出，1.1ms的高電平輸出， x = 4096 * 1.1ms ÷ 20ms = 225左右。同理求出，1.95左右的高電平，x = 407左右。因為我遙控器輸出值是1100-1998之間。結合兩者可得 throttlepercentage = (當前油門值 - 1098.0) / 830.0 ; //830是1998-1100所得。

pca9685的輸入值 = 225 + (int) (throttlepercentage * (float) (407 - 225));

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