def on_back_emf_update(obj=nil, &block)
      @on_back_emf_update_obj = obj
      @on_back_emf_update = Proc.new { |device, obj_ptr, motor, voltage|
        yield self, @motors[motor], voltage, object_for(obj_ptr)
      }
      Klass.set_OnBackEMFUpdate_Handler(@handle, @on_back_emf_update, pointer_for(obj))
    end
def on_back_emf_update(obj=nil, &block)
      @on_back_emf_update_obj = obj
      @on_back_emf_update = Proc.new { |device, obj_ptr, motor, voltage|
        yield self, @motors[motor], voltage, object_for(obj_ptr)
      }
      Klass.set_OnBackEMFUpdate_Handler(@handle, @on_back_emf_update, pointer_for(obj))
    end
Sets a Back EMF update handler callback function. This is called at a steady rate of 16ms, when BackEMF sensing is enabled.

 @param [String] obj Object to pass to the callback function. This is optional.
 @param [Proc] Block When the callback is executed, the device and object are yielded to this block.
 @example
     mc.on_back_emf_update do |device, motor, voltage|
       puts "Motor #{motor.index}'s back EMF is #{voltage}"
     end
 As this runs in it's own thread, be sure that all errors are properly handled or the thread will halt and not fire any more.
 @return [Boolean] returns true or raises an error