Digital Control of External Devices through the Parallel Port of a Computer Using Visual Basic
In this paper we carry out the digital control of external devices using the parallel port of a computer. The PC parallel port adapter that is specically designed to attach printers has been found to be useful as a general input/output port for any device or application that matches its input/output capabilities. This paper gives details and involves the design and construction of the parallel port power switching device and its associated control program (Device Controller). The Unit is capable of simultaneously and sequentially powering ON/OFF eight external devices depending on the number of bits sent to the port. However, with the presence of overflow signal to four additional ports, the unit can power up to twelve external devices. The control program causes the computer port to generate an actuating signal (the controlling voltage of 5V) which drives an electrically isolated circuit with a relay. A model of the system was built and the test result was satisfactory.
Keywords: device controller, digital switching, digital interfacing, visual basic, computer parallel port