Digital signals can be converted into analog signals through a digital / analog converter, so it can be a method to generate a digital signal and then convert it into analog signal. AT89C51 itself is a complete single-chip microcomputer, with each part of components of the microcomputer: CPU CPU, ram, Rom RAM ROM, I/O interface circuit, timer / counter and serial communication interface, as long as the 89C51 configuration interface, keyboard and display and its interface, digital analog conversion and waveform the output indicator and the interface part four, waveform generator required, the signal generator principle diagram as shown in Figure 2-3