Presently,computers mostly used in a control system. Because,the computer is high efficiency and convenience. Program writed to a computer in using replaceable complex circuits and can be easy to rectiify by solvecy at program.This project report is used computer to replace a old controller by interface between a external device and serial port of a computer. So circuit designed for interface process between a computer and a external devices and then program created to set function's work of a computer.It is satisfying controller.