code: func (c *Adaptor) ServoWrite(pin string, angle byte) (err error) {
  	pwmPin, err := c.PWMPin(pin)
  	if err != nil {
  		return
  	}
  
  	// 0.5 ms => -90
  	// 1.5 ms =>   0
  	// 2.0 ms =>  90
  	const minDuty = 100 * 0.0005 * pwmPeriod
  	const maxDuty = 100 * 0.0020 * pwmPeriod
  	duty := uint32(gobot.ToScale(gobot.FromScale(float64(angle), 0, 180), minDuty, maxDuty))
  	return pwmPin.SetDutyCycle(duty)
  }
docs: // ServoWrite writes a servo signal to the specified pin