A recent letter to Silicon Chip suggested using the TV station logos as a trigger for an ad blocker. (the logo is not present when the ads are broadcast).
While I recognise that my chances of getting this to work are slim to non existent, I think it will be educational to try.
I found a data sheet for the LM1881 sync seperator and was pleased to find a description & circuit of a video line selector in the application notes. See
I have built this but am having didfficulties getting it to work. The problem appears to be that the Vertical Sync output 'disappears' at the input to the flip-flop formed by the 74C00.
I can see the pulses on pin 3 of the LM1881, but on the other side of the .001 cap connecting to pin 1 of the 74C00, I only see a steady 5V which comes from the 2K resistor connecting this pin to Vcc. The resistor is paralelled by a diode - type unspecified, I used a 1N4148.
Has anyone here built this circuit ? Any suggestions ?
TIA
Dave