def start(self, pin, dutycycle, frequency_hz=<NUM_LIT>):
if dutycycle < <NUM_LIT:0.0> or dutycycle > <NUM_LIT>:<EOL><INDENT>raise ValueError('<STR_LIT>')<EOL><DEDENT>self.rpi_gpio.setup(pin, self.rpi_gpio.OUT)<EOL>self.pwm[pin] = self.rpi_gpio.PWM(pin, frequency_hz)<EOL>self.pwm[pin].start(dutycycle)<EOL>
Enable PWM output on specified pin.  Set to intiial percent duty cycle
        value (0.0 to 100.0) and frequency (in Hz).