Abstract: This paper presents a shaft angle to alternating current voltage to digit converter which is called the small-voltage shaft encoder. Based upon bit by bit coding of voltage comparism type it uses the small voltage code and the sign bit code to form a scheme of converting all-range angle to digit. The angular measuring element is a triangular wave rotary transformer. As the voltage characteristic of the rotary transformer is sectionally linear, therefore this coder has performance of high precision, high reliability, simple circuit and low cost.