during a half wave of the induced voltage in order to obtain a plurality of analog voltage values digitizing the analog voltage values in order to obtain a plurality of digitized voltage values and processing the plurality of digitized voltage values to ascertain the instantaneous rotation direction of the motor rotor the control circuit then can use these data to assure reliable motor start up regardless of any external driving forces which occur application_number US 83049210 A description fig1 schematically shows problems that must be taken into account when developing a u201c sensorless one phase ecm u201d after being switched on the motor is in situation 10 of fig1 i e it has either a rotation speed n 0 or if externally driven a rotation speed n u2248 0 and its rotational position u201c pos u201d is unknown to the motor 39 s electronics since a rotational position sensor is not present step 14 measures whether an induced voltage u ind is present i e whether u ind is greater than zero this can also be the case for example when a fan is being driven by wind in addition a measurement is made as to whether the magnitude of n is greater than zero if the response to both queries is no the program goes to step 12 which indicates that the rotation speed.