code: func (e *Adaptor) PwmWrite(pin string, val byte) (err error) {
  	pwmPin, err := e.PWMPin(pin)
  	if err != nil {
  		return
  	}
  	period, err := pwmPin.Period()
  	if err != nil {
  		return err
  	}
  	duty := gobot.FromScale(float64(val), 0, 255.0)
  	return pwmPin.SetDutyCycle(uint32(float64(period) * duty))
  }
docs: // PwmWrite writes the 0-254 value to the specified pin