An output port open control device (65) allows a port (P3) which outputs PWM signals of a Cos+ side to be in a high impedance state in a period in which respective PWM signals of Cos+ and Cos- supplied to a S-phase coil (22) of a stepping motor (2) are in a ground level, induced voltage corresponding to a magnetic flux variation caused in accordance with rotation of a magnet rotor (23) is generated in the S-phase coil (22), a voltage comparator (72) compares the induced voltage with a previously set threshold value and outputs presence or absence of the induced voltage, and a zero-reset judging device (66) determines that a pointer (4) is in the middle of rotation when the induced voltage is detected, and determines that the pointer (4) is in contact with a stopper mechanism (5) when it is not detected.
A method for referencing a polyphase stepper motor by monitoring the current step response in at least one driven phase is presented. The coil current step response is compared to past step responses in order to determine when an increase in or maximum load is present. A combination of step to step variance, step response variance from mean current magnitude, and average current magnitude variance, as well as other measures can be combined to create an algorithm output. The output is compared to a pre-determined threshold and if the value is greater than the threshold, the motor is commanded to halt its position, which remains magnetically synchronous. This position is then used as a reference point to zero, or to home the motor.
A speedometer includes a function storage device, which has stored therein four conversion functions, a selector, which provides four options corresponding to the four conversion functions in the function storage device, and a microprocessor, which counts pulse signals sent by the sensor device of the motor vehicle to obtain a counted total value, selects the corresponding conversion function from the function storage device corresponding to the option selected through the selector according to the quantity of poles (two, four, eight or sixteen) on the drive shaft of the motor vehicle, and puts the counted total value into the selected conversion function for calculation to obtain a car speed value.
