video signal detector

[stevee]

Hi everyone,

I'm part way through a project which will distribute component video over cat5 .. using a nice circuit from ePanorama.

One feature I would like is to have a standby mode, such that if no video signal is being received, the cat5 drivers are switched off. I've looked, but cannot find a reference circuit for this.

A circuit that could give a boolean result if the average input voltage > 0.3v would suffice .. I think. Thoughts, ideas appreciated.

Cheers,

Steve

 

[Paul Obrien]

you could try a LM1881, I'm sure these little work-horses could do it.

 

[Nigel Goodwin]

Slice the sync off the video with a sync seperator, then use that to feed a 555 connected as a missing pulse detector (essentially the incoming pulse discharges the capacitor and stops it timing out) - once the sync pulses cease, the 555 will time out normally. You can obviously adjust the 555 timing for how long you want this period to be.

 

[stevee]

Thanks for the info.

I've found a circuit that with an LM1881, it uses the sync pulse to charge a capacitor .. thus giving the +ve indication I need to switch a relay. If this doesn't work, then I'll try the 555 missing pulse circuit.

Cheers,

 

[Nigel Goodwin]

Thanks for the info.

I've found a circuit that with an LM1881, it uses the sync pulse to charge a capacitor .. thus giving the +ve indication I need to switch a relay. If this doesn't work, then I'll try the 555 missing pulse circuit.

Basically both the same thing - missing pulse detectors - the capacitor charging version though will initially mute the video until it's charged sufficiently to un-mute, but this obviously isn't a problem for this application.