VGA Monitor Splitter and Extender

Figure 1 

The circuit was designed to provide distribution, extension and splitting of personal computer video output to two or more monitors.

• Super Video Graphics Array (SVGA) – defined in 1989 as a set of graphic standards that supports 800 X 400 resolution or 480,000 pixels with support for 256 colors or a palette of 16 million colors
• Pixel – short for picture element, is the smallest point or single item of information in a graphic image and the basic unit of programmable color on a computer image or computer display
• 2N3906 – a common PNP BJT transistor intended for medium voltage, lower current and power, which can operate at moderately high speeds, used for general purpose switching and low-power amplifying applications

The circuit may also be called as video port expander, multiple monitor, PC video splitter, LCD Y splitter, etc. It provides the same high resolution image to several monitors using a single PC. Each line of the SVGA card of the analog output stage of PC contains 75 ohm impedance being obtained from the signal sources. The transistors will not contribute as additional loads as they are having very high input impedances. The parameters being shared are the primary colors which consist of Red, Green and Blue, the horizontal synchronization and the vertical synchronization. Since the three ID connections are supposed to be connected to less advance and cheaper monitors, they can be excluded in the circuit.

The PNP switching transistor 2N3906 forms the emitter-follower mode of ten transistors. They are utilized due to their low current having a maximum of 200 mA, low voltage with a maximum of 40 Volts, low cost, versatile and efficient, although they are not the best possible choice. It is preferable to use faster transistors when dealing with higher pixel rates because high input resistances will be supplied by higher gain. The resolution entirely dictates the quality of a display system as to how many bits are used to represent each pixel and how many pixels it can display.

To prevent RF interference on the circuit, as the monitor operates in radio frequency, a metal casing should enclose the splitter circuit and eventually be connected to ground. The circuit will require a power supply of 5 Volts and a current around 600 mA. The DC components in the output signals will not be considered as drawbacks since the splitter is working well with 1024×768 15” and 800×600 monitors.

The 2N3906 transistor is intended for amplifier functions and high-speed switching in industrial applications.

Since there are many standards that have followed, all are employing the standards of SVGA since 1990 which includes the eXtended Graphics Array (XGA) of IBM, Super XGA (SXGA), SXGA+, Ultra XGA (UXGA) and Quad XGA (QXGA). This video splitter will be suitable for tradeshows, in-store displays or classrooms where high quality video on multiple monitors is need; for support with LCD flat panel monitors and DDC2B protocol; in digital signage applications with perfect resolution; for supporting 1900×1200 resolution without degradation; for burn-in of monitors after repair; and for support of stereo audio as well.

Source:www.zen22142.zen.co.uk/Circuits/Misc/monitor.htm