PCA9685.py 文件源码

def set_pwm_freq(self, freq_hz):
        """Set the PWM frequency to the provided value in hertz."""
        prescaleval = 25000000.0    # 25MHz
        prescaleval /= 4096.0       # 12-bit
        prescaleval /= float(freq_hz)
        prescaleval -= 1.0
        logger.debug('Setting PWM frequency to {0} Hz'.format(freq_hz))
        logger.debug('Estimated pre-scale: {0}'.format(prescaleval))
        prescale = int(math.floor(prescaleval + 0.5))
        logger.debug('Final pre-scale: {0}'.format(prescale))
        oldmode = self._device.readU8(MODE1);
        newmode = (oldmode & 0x7F) | 0x10    # sleep
        self._device.write8(MODE1, newmode)  # go to sleep
        self._device.write8(PRESCALE, prescale)
        self._device.write8(MODE1, oldmode)
        time.sleep(0.005)
        self._device.write8(MODE1, oldmode | 0x80)