How to detect the presence of a video signal.

pcleats

Hello all,

My question is this. is there a way to get the Propeller to detect the presence of a video signal. I have an application where I would like to be able to detect if an active video signal is connected without having to use a monitor. I need to be able to detect up to 8 seperate video sources at once.

Any suggestions?

Thanks

Patrick

Rayman

Perhaps you could use a circuit like that Perry uses in "stupid video capture" to detect the vertical sync signal... If you get this a 30 Hz, then you have video...

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My Prop Info&Apps: ·http://www.rayslogic.com/propeller/propeller.htm

localroger

If you are *only* interested in valid video versus no signal at all, all you need to do is detect the voltage swing. You can do that with the delta-sigma ADC scheme. You need a counter for each ADC, and two pins, so 8 will use up most of a prop. All you need to do is check periodically; the period doesn't even matter. If you get more than a certain swing for more than say 20% of samples (you're really looking for sync pulses) you declare the signal to be there. You can do this sampling very fast at low bit resolution (you gotta love the prop letting you trade bits for sample rate in software).

Incidentally, I will probably be posting an ADC question myself here soon because I'm having problems in an app where I need more accuracy, but for video detection all you need is maybe 8 bits and with that you can sample very, very fast.

Phil Pilgrim (PhiPi)

You don't need a full-blown ADC implementation. Bias the input pins just above or below Vdd/2 with a resistive divider and capacitively couple them to the video signals. When a signal is present, you will see changing logic levels on its respective input. This will save cogs, since there are only two counters per cog, and you won't need any counters.

-Phil