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LM1881 is used to do all the grunt work of separating the sync signals from the composite video. The chip provides the vertical sync on pin 3 for the vertical oscillator, and composite sync on pin 1 for the horizontal oscillator. The intensity signal comes from the composite video signal itself, but is negative. I didn’t really mind since this circuit took only 10-15 minutes to slap together. If an inverter is preferred to make the video “positive” then here is a schematic for the inverter below as taken from the VGA-Scope converter. This circuit includes another 555 to generate the negative supply rail for the op-amps.

VGA-Scope converter

VGA-Scope converter

555 to discharge the capacitor for synchronization

555 to discharge the capacitor for synchronization

74hc74 video syncron 74hc00

74hc74 video syncron 74hc00