运用proteus绘出的电路板，程序请联系我，我给你。-use proteus design PCD for speaker. it is good for your use.

51单片机和PC联机的小程序，特别适用于Proteus 7 Professional和Keil uVision4的初学者学习使用，已验证OK-51 microcontroller and PC online applet, especially for Proteus 7 Professional and Keil uVision4 beginners learning to use, has verified OK

proteus仿真程序，使用2片74HC595连接数码管（显示数字）改进后无重影-proteus simulation program, using two 74HC595 connecting digital (digital display) improved after no ghosting