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missing sync ?


Terry

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I was just wondering why a lot of the tapeless video recorders crash when they loose the video. Is it simply that they need to see sync pulses or is there more to it ?

How hard would it be to make a little box to produce the signals required when the video is lost ?

Maybe a MAX LOS chip could be used ?

Any thoughts ?

Terry

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That kind of solution would probably have good success if the display device could withstand a few hundred milliseconds of lost video. In your installation, are brief periods of lost video tolerated? If so, how long does the source video need to be messed up to create a lock-up condition?

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If it can sustain that long a period then artificial syncs that are gen-locked to the original source do not seem to be needed. If that turns out to be true, then the solution is much less complex.

Do you have a video rescaler box sitting around? These are standalone devices that convert one video format to another. For example, PAL to NTSC.

Or, do you have a VHS "tape restorer" device to try?

Or, a BOB4 OSD board collecting dust?

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I do have a CBT 100 that sends a colour bar when the video is lost but it seems to not cut in quick enough, I can still see up to 2 seconds of mush before it cuts in.

Maybe I could use Oracle to switch to a wired camera ?

I will give it a go tomorrow :)

Terry

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There are a number of ways to approach this, some of which could be very sophisticated. But, I would say that it would be worth a simple experiment before deciding what to do. Here is what I suggest:

Take one of your little MAX7461 loss of sync alarm IC's and have it control a SPDT relay. The relay will be used switch over to a backup video source (old camera aimed at a photo of a skull and crossbones) upon loss of video.

I suspect that your 4-way diversity will be involved at some point. With that in mind, there are some really cool things you could do if you wanted to toss $125 and a manweek of effort at solving the DVR video lockup issue. :)

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If it does switch to the standby video, how will it automatically switch back?

Sorry I was not very clear as to my thoughts (too close to bed time). What I ment was that I could use Oracle to let me test switching between 2 video sources to see if it would crash before I go to the trouble of building a purpose bilt unit.

Take one of your little MAX7461 loss of sync alarm IC's and have it control a SPDT relay. The relay will be used switch over to a backup video source (old camera aimed at a photo of a skull and crossbones) upon loss of video.

If this works then I will be very happy :D

I suspect that your 4-way diversity will be involved at some point. With that in mind, there are some really cool things you could do if you wanted to toss $125 and a manweek of effort at solving the DVR video lockup issue. 

I can't help thinking a little re-jigging of Oracles code would be a good start, you dont want a little project do you :rolleyes:

I will let you know what I find.

Terry

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OK, I did the test with Oracle but he didn't like 2 different video feeds, he just kept switching between the 2.

Even with this constant switching it took 1 min 10 sec for the DVR to crash the first time and 4 min 42 sec the second time. The question is why did it crash at this point ?

How hard is it to gen lock a second feed ?

Even if my unit dose not require this it may be good for other DVR's.

I need to give this a lot more thought.....

Terry

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simply feed your video thru a framestore

Can you expand on that Thomas ? I thought a frame store was for capturing a frame, if it can be made to repeat the last good frame until a new good one is found that would be fantastic. Can you point me to a unit please ?

Terry

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I can't help thinking a little re-jigging of Oracles code would be a good start

Yes, it could be modified. But, market-wise, Oracle would not be a cost friendly solution for this.

How hard is it to gen lock a second feed ?
You'll need a video scan converter if you want to fully protect from all acts of video corruption. That takes lots of Ram, complex circuitry, and such. That is why I asked if you had a video rescaler box. These are often based on a scan converter design, but obviously not all. Here is an example of a fellow that used one to fix up nasty VHS tapes: http://www.unterzuber.com/TBC.html

I think a possible solution would involve a BOB4 OSD and your host PIC. It might solve your problem. Plus, it will give you a chance to fully annotate your 4-way diversity with some useful text/graphic data.

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OK, so full protection is out but I dont see how a rescaler box will help if the video completely drops.

The BOB4 is a nice idea and would look very flash but I dont 'need' the extra info so I think i will try the simple idea we started with.

Terry

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but I don't see how a rescaler box will help if the video completely drops.

Some continue to provide the syncs when video is lost (either as repeated last frame, black video, or a traditional blue screen). But sorting out which one you need would be a big effort.

The BOB4 is a nice idea and would look very flash but I don't 'need' the extra

Of course you do. Just imagine your 4-way diversity with: active antenna indicators, RSSI histograms, out-of-range alerts, antenna performance reports, visual battery alarms, custom text annotations, and so much more. Plus, it should solve your DVR lockup problem. :)

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Of course you do. Just imagine your 4-way diversity with: active antenna indicators, RSSI histograms, out-of-range alerts, antenna performance reports, visual battery alarms, custom text annotations, and so much more. Plus, it should solve your DVR lockup problem. 

I can see what you are driving at, it would be nice to have those features at times BUT I don't have time to build another 4 way system just now. I'm sure I will at some point but my new system is working very well so I don't NEED to build MKIII just yet.

Some continue to provide the syncs when video is lost (either as repeated last frame, black video, or a traditional blue screen). But sorting out which one you need would be a big effort.

Dose the BOB4 do any of these things ?

If it dose I may reconsider ;)

Terry

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Thanks Thomas, I am going to have a go at the simple solution using the MAX LOS chip and a 4311 in the hope of getting it working quickly but you have sparked my interest in the BOB board so I have added it to my 'list' ;)

Terry

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  • 2 weeks later...

I have built the circuit and tested it using various video feeds and all is well :)

If connected to 2 receivers on the same channel it works as an effective 'poor mans diversity system'. So if you don't have the cash for a propper system then why not build one like this, the chips are free samples from Maxim ;)

And would be even better if used as a switching system for a patch and a omni :D

I have still to box this up so I can test it for my intended purpose. When connected to 2 cameras it takes a frame or two to settle and I hope this won't crash my recorder :unsure:

Terry

post-6-1197461640_thumb.jpg

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