Advice needed: Anti LCD Bluescreen device

[after.burner]

[Edit] Sorry, posting overlapped so this does not take your last post into account


@Microtronics: As for removing/inserting syncs this is also something Thomas Scherrer suggested here:

you can make a system that is analog and does something like this:
take two sync separator IC's like LM1881
one is connected to incomming video, its output pulse is connected
via a high ohm resistor to a 15khz oscilator,
this osc is adjusted to be quite accurate, incomming pulses will make the oscillator
"lock" to the incomming pulses, and the lock resistor must be so high it takes a few sec
to get in lock and stay in lock when signal is lost, now feed this osc signal into another
1881 and get a nice locked sync pulse for your video,
the incomming synd is clipped away, and the new filtered sync is inserted
this kind of circuit will take a few hrs for an electronic wizz to make :-)

However I do not fully understand his post: Ok, use an LM1881 to extract composite sync -> fine. Use this to injection-lock an oscillator so that it will have the right freq and not lose it if the input is off for a while -> ok.

However I fail to see what to do with the second LM1881: According to its datasheet the LM1881 does not remove sync signals from the source but simply extracts the sync pulses. Also it can not insert sync pulses. This could work fine with the sync remover/inserter you mentioned above. Seems like a lot of work though


[Edit]
The application note referenced by Microtronics uses parts that do not seem to available any more (HFA1115, HFA1135). Here is a similiar schmatic for sync-stripping that uses the OPA698, which is still available (although it's quite expensive in europe at 5,50€/piece).

[Mictronics]

I don't know either, in my opinion there is no need for a second LM1881. A simple 8pin AVR like ATtiny25 should be fine for the oscillator job. 15.625kHz can be generated from a crystal using an internal AVR timer.
I think the analog circuit needs more attentions to keep the video signal in good shape.

[after.burner]

Thanks for all the help so far. Will continue to work on this as soon as time permits. If somebody wants to join me or do the analog part for a sync remover / inserter: Always welcome

[after.burner]

Detecting missing hsyncs by using composite sync output of the LM1881 is probably not a good idea: Composite sync will go wild if the LM receives static:


(Composite sync out on an LM1881 which receives static from an RC305 RX)

So the number of composite syncs / sec *increases* on bad signal and does not decrease.

I tried to count the composite syncs with an Atmel Mega 328 16Mhz by using pin change interrupt -> not a good idea. I think that at this rate it simply can not keep up even if you just increase a counter in the interrupt routine.

So I guess I'll have to find a way around this ...

[Mictronics]

The LM1881 provides some more outputs. May you try looking at some more outputs in combination to detect a bad video signal.

[daronj]

I have searched many options for removing blue screen as well. My setup is simple, cheap and bypasses the blue screen 100%. I simply use a 13" LCD tv ($99), but instead of using the video in, I use an RF modulator ($20) that sends the video signal to channel 3 or 4 (you select). Works perfectly and displays 100% static without going to blue screen.

I have also successfully used an LTS Composite to VGA converter to send my video signal to the VGA port of a computer monitor. This also removed the Blue Screen issue, but my Composite to VGA converter did not last very long (it was a cheap one). Good quality VGA converters were more costly than the TV and RF modulator combined, so I went with the RF.

Daron

[softlad]

Does using an RF modulator affect the image quality compared to composite?

[daronj]

Does using an RF modulator affect the image quality compared to composite?

I believe in theory, there is probably some degradation of the signal. However, I have not found any noticeable reduction in quality. I find the video perfectly acceptable and my OSD data looks fine.

[after.burner]

daronj, thanks a lot for your input. I tried an composite->vga converter with no luck so I am afraid it depends on the model you chose. As for the RF modulator: That sounds pretty interesting! Unfortunately my LCD device has no tuner, only AV in

[daronj]

daronj, thanks a lot for your input. I tried an composite->vga converter with no luck so I am afraid it depends on the model you chose. As for the RF modulator: That sounds pretty interesting! Unfortunately my LCD device has no tuner, only AV in

Yes, I think you're right. Some of the VGA converters have the blue screen circuit built in. No tuner, Ah! I was in that boat as well. I started out using a nice Dell 20" monitor that has composite in as well. The blue screen was very sensitive, so that's when I tried the LTS VGA converter. When that pooped out, I couldn't find an affordable alternative. I even explored using a simple $8 osd from Hobbyking on my ground station to keep the video alive, but others tried it with no success. That's when I gave in and bought the little 13" Craig TV (it runs off of 12v). Even without the RF converter, the TV shows a good bit of static before going to blue. It also comes back from blue more quickly than others that I have tried. Still, in a critical situation, if there is any usable video, even the horizon contrast between the sky and ground, I want to see it. So I decided to put the RF modulator on the back. It's pretty compact and I have it all wired to run off of one 2200 mah lipo. Still rather have goggles though