Power SuppliesSignal Generators

CGA-SCART adaptor

The signals from the CGA’s R, G, and B pins are converted from TTL to SCART levels using resistors R4, R5, and R6 and the scart inputs’ entry impedance (75).

The adaptor has the great advantages of not needing a separate power supply and requiring so few external components that these can easily be accommodated in the SCART connector.

The signals on the R, G, and B pins of the CGA card are converted from TTL level to SCAM level with the aid of transistors R4. R5 and R6 and the input impedance (75 Q) of the SCART inputs. The output impedance of the so-created voltage dividers is not exactly 75 Q as specified for SCARF video inputs, but in practice, this_ does not appear to make much difference. Resistors RI-R3 between pin 6 of the CGA card and the R, G, and B pins of the SCAM connector ensure that the brightness is brought down to 50% when pin 6 is active. A composite sync(harmonization) signal and a blanking signal for the TV are derived from the horizontal and vertical sync pulses of the CGA card with the aid of R7–R1 1 and

The 5 V supply for T1 is obtained from the CGA card via pin 7. Since that pin is not normally used, it must be linked to the 5 V line by a short length of wire.

CGA-SCART adaptor Schematic diagram

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