Abstract: A mobile medical diagnostic device having a mobility chassis with two supporting wheels and a central steerable drive wheel. The device has an electrical power steering system controlled by two synchronized handles operable by wrist action of an operator walking behind the device. The handles include a rotatable grip for controlling the velocity of the device. Advancing the grip actuates the throttle to the drive wheel and retarding the grip actuates a proportional electromechanical braking system. The device includes a proximity detector system which uses ultrasonic transducers to determine when an obstacle is within close proximity to the device, and automatically actuates the brake system. A window signal is established on the basis of both a preselected distance from the device within which it is desirable to apply the brakes, and a delay function which is determined by the distance of the front portion of the device from the transducer.