Practical Electric Speedometer System for Passenger Car Applications

A digital implementation of an automotive electronic speedometer was developed to maintain the present analog pointer display while offering the advantages of increased accuracy and stability, reduced size and weight, enhanced acoustical performance, and improved styling and design flexibility.

System cost is minimized by using custom integrated circuits with conventional electromechanical device technology. The speedometer is mechanized using an air core gage movement driven by digital electronics. The odometer is a conventional wheel display modified for stepper motor drive. Vehicle speed sensing is performed by a transmission mounted PM generator.

This paper addresses design considerations and features of this system.