I'm trying to build a circuit that gives the user the option of using the functions of a particular IC or not. In this case, the LM1881N which is a sync stripper. It is fed a composite video signal, removes the video information and outputs a composite sync signal (csync) which will then go to a monitor. I want to have the option of switching between composite video and csync but I'm unsure of the simplest method of switching. I've considered a DPDT switch that will bypass the IC and send the composite video signal directly to the monitor but I'm not certain if this will work or what possible ramifications this option may have.

  • 2
    \$\begingroup\$ First, to make sure you're not using the wrong chip for the job--are you aware that the IC you mentioned takes a composite input, not a component one as mentioned in the question? \$\endgroup\$
    – Hearth
    May 13 '17 at 23:05

The simplest approach here would be a bilateral switching IC, like the 4066B. This part behaves similarly to a set of mechanical SPDT switches, but each switch can be digitally controlled. Connecting one input to the composite video output and the other to the output of the sync stripper would achieve your goal perfectly. (And you'd be left with three more channels to use for other tasks.)

  • \$\begingroup\$ Video lines may be 75-ohm terminated. Thus buffers (Common Collector, or opamp) are needed after analog muxes. \$\endgroup\$ May 14 '17 at 4:24
  • \$\begingroup\$ Thanks for the help. This looks like a good solution. Is it significant that the the LM1881 will still be active? Should the power supply to the chip also be cut or maybe it's no relevant? \$\endgroup\$ May 14 '17 at 15:21
  • \$\begingroup\$ No, leave the LM1881 alone. Removing power to a chip that's receiving an input is bad. \$\endgroup\$
    – user39382
    May 14 '17 at 17:13

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