Switching on basis of type of composite video comparison

[frozenfire_981]

hi,

I modified a CRT based oscilloscope into a coloured LCD oscilloscope. the video controller card that i am using accepts coloured and monochrome videos at two different ports to display it on LCD. Every time i change the input video type (i.e coloured or monochrome), i have to manually change the connector on the video card. I am trying to find an IC which detects the input type (i.e coloured or monochrome) and sends a flag. using this this flag i will to switch a relay with micro-controller which to change the connection of the input video to the two ports of video controller card.

Till now i can't find an IC which can perform this switching. any suggestions plzz......

 

[betwixt]

More information needed:

What exactly is the difference between the colour and monochrome video signals?
Are they the same sync speeds and video levels?
Is the monochrome signal a single wire or is it RGB with the same video on each of them?
Are these signals digital, composite or plain analog and if the latter, are the sync signals individually available?

Brian.

 

[frozenfire_981]

composite video is almost same for both coloured and monochrome, except for the colour burst in the coloured video after sync pulse.
sync speeds--> i didn't measure. do they matter ?
video level is 1V Peak to peak for both.
both mono chrome and coloured are single wired (on RCA jack in RS-170 standard format).
both these signals are analog video signals
--monochrome --> green video with sync on it
--coloured--> coloured video with sync on it

 

[betwixt]

Thanks, that makes it clearer.

I can see two possibilities, one is to look for the colour burst, the other is to see if the green channel has sync on it. Normal RGB will have no sync on the green because both syncs are sent on their own cables. In this case, I think looking for colour burst is probably the best option.

You can either use a sync seperator IC (LM1881 for example) to remove the active part of the video waveform and see if any subcarrier is present on what remains or better still, if your video is PAL encoded, use the presence of the ident signal (subcarrier phase change on alternate lines) because that will be immune to possible subcarrier frequences appearing in the rest of the video signal. It would be worth investigating domestic colour decoder ICs as these usually have a pin to signal whether the video contains subcarrier in order to tell the rest of the TV to switch to monochrome mode. With that signal you could directly control the routing of your video inputs. Most decoders ICs use delay lines and the likes which might be difficult to find these days but as they are used in the decoding process rather than the colour detection stages, you can probably leave them out of circuit.

Brian.

 

[frozenfire_981]

thanx Brian for your help..

what i found is, that there is a voltage difference between the two signals..

monochrome = 0.3Vpp
coloured = 1Vpp

should i go for envelope detection or some other technique ??