Here is the schematic for the colour overlay prototype I have been breadboarding. The next logical step would be to design a proper circuit board. However I’m not happy with it for a number of reasons:

  • Too many ICs, too complex
  • Not able to support both video standards at the same time (need to select either a PAL or NTSC crystal)
  • Doesn’t work reliably with PAL, in any case because the PAL colourburst changes phase on each line and it is a 50/50 chance that the AD724 will change phase in the opposite direction to the incoming signal
  • The MC44144 is an obsolete part

I want to explore other alternatives. I have a few ideas. However for the time being I’m taking a break from analog video. My son needs an alarm clock so I’m going to build him one!