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'[EE]: rapid switching between two composite NTSC s'
2001\01\07@141146 by Stephen B Webb

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I have a stereo camera head which has two small CCD cameras, and can
output the following NTSC signals:

1.  One separate signal per camera, simultaneously outputting both signals
(one composite signal per camera).  I believe that these two signals have
the same sync signals.

2.  One signal that is interlaced as follows:  Even fields from camera 1,
odd fields from camer 2.


I also have a head-mounted stereo display device which expects a frame
interlaced NTSC input.  Baically it displays FRAME 1 (two fields) on the
left display, and FRAME 2 (the next 2 fields) on the right display.

I would like to hook these two devices together in order to get real-time
remote stereo input to my eyes.

SO...What [I think] I need is a circuit which takes the two in-sync
composite inputs, and alternates between the two signals to output a
single signal which is appropriate for the head mount display.

My plans are to get a circuit (any suggestions?) that can detect the start
of a frame, and then with a little logic, switch between the two inputs.
What I am concerned about is how this switching circuit will affect the
sync signal on the outgoing signal.

Anyway, I'm looking for input from anyone..

Thanks
-Steve

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2001\01\07@164605 by Chris Carr

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Hi Steve

In effect you are creating an update at 15Hz on each eye which seems like a
good headache generator if used for any period of time. Plus if there is any
tendency for epilepsy you are operating at the upper end of a flicker rate
that could induce fits. (Even worse in 50Hz regions where the flicker will
be 12.5Hz).

I would personally recommend using a dual link (either physically or
virtually) and thus maintaining the 30Hz frame rate, Particularly if this is
a commercial product and given the fact you are specifying a 60Hz product.

However for Frame Extraction

The classic IC is a Nat Semi LM1881
http://www.national.com/

However Elantec produce arguably superior products with the
EL1881, EL4581 and EL4583
http://www.elantec.com/


Full Pin Compatibility with all products

Regards
Chris

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2001\01\07@180727 by Bob Ammerman

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The two signals are almost certainly commonly synced.

This means that if you switch during the VBLANK period you will almost
certainly get good results.

This could be done by a simple sync separator circuit and a flipflop or two,
driving an analog switch.

Bob Ammerman
RAm Systems
(contract development of high performance, high function, low-level
software)


{Original Message removed}

2001\01\08@090516 by Olin Lathrop

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> 1.  One separate signal per camera, simultaneously outputting both signals
> (one composite signal per camera).  I believe that these two signals have
> the same sync signals.
>
> 2.  One signal that is interlaced as follows:  Even fields from camera 1,
> odd fields from camer 2.
>
> ...
>
> SO...What [I think] I need is a circuit which takes the two in-sync
> composite inputs, and alternates between the two signals to output a
> single signal which is appropriate for the head mount display.

A stereo head mounted display already has two separate monitors, one for
each eye.  You should be able to use the two separate camera signals
directly.  The interleaved field signal is for single-monitor stereo
displays that require a screen shutter, polarizer, shutter glasses, etc.


*****************************************************************
Olin Lathrop, embedded systems consultant in Devens Massachusetts
(978) 772-3129, spam_OUTolinTakeThisOuTspamembedinc.com, http://www.embedinc.com

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2001\01\08@151424 by Peter L. Peres

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Your switching speed requirement is low. You have about half a line of
time to switch over, that is 15 usec, and a 4066 gate will work.

A circuit to detect the frame signal can be built by using a standard sync
separator. This outputs an even/odd signal. By counting this with a
flipflop you will obtain your required switching waveform.

Peter

PS: imho you are speccing the viewer wrong. Unless it contains a TBC it
will flicker something terrific. Even if it does contain a TBC it will
cause delay between what you see and what happens such that it will cause
motion sickness and other problems with a simulator/remote manipulation
application.

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2001\01\08@162340 by Stephen B Webb

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> PS: imho you are speccing the viewer wrong. Unless it contains a TBC it
> will flicker something terrific. Even if it does contain a TBC it will
> cause delay between what you see and what happens such that it will cause
> motion sickness and other problems with a simulator/remote manipulation
> application.

"It's what I've got..."

This is a one-off type of deal.  We happen to have a stereo headmount
display sitting around, and a stereo camera rig.  They speak somewhat
different signals, and I want to hook them together.

Flicker does't seem to be a problem hen we use it "as intended" (ie watch
the "3D" demo tape that comes with it.)

I would classify this as a toy much sooner than I would classify it as a
simulator / remote manipulation application.


Anyway, I think it will work for what I want.

Thanks for hte help

-Steve

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