Abstract: Circuitry (100, 100') for determining actuator position includes four MOS transistors (T1-T4) connected to each side of a bi-directional motor (10). The current flowing through the motor (10) at any given time is proportional to voltages developed across the internal impedances of the transistors (T1-T4). The resulting motor voltages are amplified and high-pass filtered to remove any DC offsets due to the signal amplification. The conditioned motor voltages are then compared to one or more threshold voltages and passed through a one shot circuit (120) to provide detectable pulses for each motor commutation event. Circuitry (106,107) is provided for counting pulses provided by the one shot circuit (120) and, based on a desired motor position, for providing a number of digital control signals to a digital control circuit (104).

Abstract: An actuator for automotive HVAC control is coupled to a remote controller by two wires. The controller applies power to the actuator in a high current or a low current mode. A variable resistance driven by the actuator generates a voltage proportional to position in the low current mode. Zener diodes in the actuator circuit prevent motor operation in the low current mode and permit motor operation in the high current mode. A microprocessor in the controller selects the mode and reads the voltage in low mode to determine position. It controls the motor for a duration required to reach a desired position and then checks the new position to verify that the target has been reached. If not, another iteration is employed to reach the target.