VGA to TV converter

  
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Here is the circuit for VGA to scart connection. It is basically a circuit which takes VGA signals and converts it to RGB + composite sync signal which can be fed to TV via SCART connector. VGA card picture components RED, GREEN and BLUE are already at the correct voltage level (0. 7Vpp) and has correct impedance (75 ohm) for direct connection to c
VGA to TV converter - schematic

orrespondign inputs in the TV. What needs to be done is to combine separate horizonal and vertical sync signal from VGA card to one composite sync signal which is feed to TV video in pin in SCART connector. This sync signal conversion is done by the electronics in the circuit. The circuit has also sends correct level signal to the TV RGB input enabling control pin in the SCART connector (pin 16). This circuit is designed for converting normal VGA signals standard RGB signals and composite sync signal. The circuit is quite simple, because RGB signal ouput from VGA card is already standard 0. 7Vpp to 75 ohm load. RGB+composite video format is the signal format needed by the TV input. Besides that format conversion special drivers is needed to set the VGA card to suitable refresh rate for normal TV. For sync signals there is a circuit which combines horizonal and vertical sync signals to from composite sync singals. The circuit is simply based on one TTL chip with four XOR ports, two resistors and two capacitors. TTL chip was logical choise because VGA sync signals are TTL level signals. The sync signal combiner has a system to adjust to different sync polarities so that it always makes correct composite sync signals. VGA card uses different sync signal polarities to tell the monitor which resolution is used. This circuit adjusts to sync signal polarity changes in less than 200 milliseconds, which is faster than setting time...



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