说明：  基于单片机与光电传感器的电动自行车速度与里程表的设计
(A variety of motor is widely used in industry, in order to facilitate the conduct of motor control, monitoring, speed control, it is necessary to measure motor speed, thereby enhancing the degree of automation. At the same time, the circuit can be applied to expand its functionality, with the function of measuring frequency, and therefore make the following basic requirements for circuit)