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This paper deals with the design of electronic system used for changing the transmission ratio of a rubber belt electro-mechanical continuously variable transmission (CVT) for motorcycle applications. The rubber belt CVT has input pulley, output pulley and a rubber belt which connects the input pulley to the output pulley. The belt transmits the speed and torque from the input to the output pulley by means of contact friction between the belt and the pulley surfaces. Each pulley set consists of one fixed and one sliding pulley sheaves. The axial position of the input sliding pulley sheave is controlled by an electro-mechanical system. This system utilizes the DC servomotor, actuator gears and cam mechanism. The sliding sheave of the output pulley is continuously pushed by contra spring to mantain the belt tension and prevent belt slip. By controlling the axial position of the input sliding pulley sheave, the input belt-pulley contact radius can be varied, hence changing the output belt-pulley contact radius and finally changing the transmission ratio. The axial displacement of the input sliding pulley sheave is detected using a two channel incremental encoder, while the rotational speeds of input and output pulleys are sensed using one channel incremental encoders. By knowing these two speed values, the transmission ratio of the CVT can then be determined. The microcontroller system of Arduino is used as a main controller to perform the transmission ratio changing of the CVT system. The results show that the electronic system can perform the CVT transmision ratio changings adequately.