VGA to RGB converter

  
First circuit is for connecting VGA card to video projector or a monitor which accept VGA card frequencies and has RGB + Composite sync input. This circuit has been succesfully used with Electrohome Projection Systems ECP 4100 data and video projector. 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. For sync signals there is a circuit which combines horizonal and vertical sync signals to form composite sync singals. The circuit is simply based on one TTL chip with four XOR ports, two resistors and two capacitors. TTL chip ws logical choise because VGA sync signals are TTL level signals.
VGA to RGB converter - schematic

This circuit has been succesfully used with Electrohome Projection Systems ECP 4100 video projector in many VGA and SuperVGA modes. The circuit have been also used succesfully with one old Barco video projector using my VGA to TV drivers to get the VGA card to generate suitable signal frequencies which that old video projector can handle. Component list C1 22 uF 10V electrolytic C2 22 uF 10V electrolytic R1 2.2 kohm R2 2.2 kohm R3 1.8 kohm R4 1.8 kohm R5 2.7 kohm R6..R8 47 ohm U1 74LS86 or 74HCT86 T1 BC 547 T2 BC 547 TTL level sync signal Many computer monitors have been designed to accept TTL level sync signals. If you happen to own a monitor which uses TTL level sync signals the circuit above does work with with it, because the sync signal level from that circuit is not enough for the monitor. I have designed another simpler circuit for monitors which need TTL levels.



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