How to make a VGA to RCA interface converter

I often encounter the need to connect a large-screen color TV with a coaxial RCA input socket to the VGA interface of a computer and other equipment as a display. The solution is to configure an interface converter. The circuit in the picture plays a role of a conversion bridge between two different interfaces.

In the figure, the VGA interface outputs the R, B, and G three primary color signals and are respectively coupled to the RCA output port through the C1C2, C3C4, and C5C6 circuit groups. At the same time, the coupling capacitor blocks the DC component from the video card. The ICa, ICb exclusive OR gate (74HC86) synthesizes the horizontal and vertical synchronization separation signals into a composite synchronization signal, and outputs it to the synchronization signal phase conversion circuit of DOS and Window operating system composed of S1 two-way toggle switch and field effect transistor T1. Since the composite sync signal and the green primary color signal are on the same channel, it will cause the display to be too bright, so you can slightly reduce the resistance of R2 to reduce the brightness, and adjust the resistance of R1 and R3 appropriately to balance the three primary colors, but pay attention Do not overload the video card and cause overheating. The input voltage of the power regulator IC2 cannot be lower than 9V to ensure that the converter can maintain a constant 5V working voltage and 30mA working current. D2 is a protection diode for reverse polarity of the DC power supply. The circuit board is placed in a shielded box with a grounded metal shell. To prevent external electromagnetic field interference.

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