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I want to build a circuit for my car (It has two cameras, front and rear) that shows me the front and rear camera in the same screen (splitted), top half the video from the front camera and bottom half, the video from the rear camera.

The cameras are the "regular" cameras used in cars as "backup cameras".

Is this possible with a DIY circuit?, any ideas about how to build the circuit?

The screen will be the one in the Pioneer aftermarket dvd radio

Barenca
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I did almost exactly the same thing about 7 years ago. It was called the "video squeezer", it took 2 analog video streams and output 1 video stream, except in this case it was left/right instead of top/bottom. The cameras were triggered simultaneously.

Doing left/right has the advantage of needing very little buffer (as long as they are reasonably in sync), while with top/bottom you need to buffer at least one whole frame. Embedded memory was plenty for buffering a couple of lines, but I don't think it would be enough for a full frame (at least not with a cheap FPGA).

The design basically used two ADV7180 to digitize the incoming video streams, the digital output went to an FPGA (Spartan-3AN) which subsamples and combines the two digital streams into one, and the output is sent to an ADV7171 to generate the analog out.

apalopohapa
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    I think in this case whole frame buffering is unavoidable as it doesn't seem like the cameras will be locked together. An external DRAM big enough for a couple of frames costs a couple of bucks, so it's not that big of a deal. – alex.forencich May 22 '15 at 00:20
  • Left/right split is OK for me. Could you share more details of what you did?, a schematic with part numbers would be great! :) – Barenca May 22 '15 at 16:49
  • @Barenca Can the cameras be synchronized (do they have a trigger input)? – apalopohapa May 25 '15 at 02:46
  • Yes, they have a trigger input. After a little research It seems that It is not a task I could achieve with easy to do circuit, so I was wondering if a cheap DVR could help – Barenca May 26 '15 at 11:53
  • Can you provide some more information about the video squeezer stage in the Spartan 3AN, or perhaps something actionable that an enterprising chap may examine if he is trying to do the same – Skyler Oct 24 '16 at 07:31
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Yes. You will most likely need to use a small FPGA with a pair of video decoder chips and a video encoder chip. Or possibly an SoC of some sort with video input and output capability. Recale the two input streams on the fly, possibly by discarding lines, combine the two, and send it on its way. It would probably be easier to replace the screen with one designed for security applications that can do this internally.

I should mention that this would probably be a pretty interesting project if you are interested in getting in to FPGA development. I almost did some consulting on something like this for use on RC drones a while back, but it was determined there wasn't sufficient interest to continue. The design would be simple enough, a couple of composite video encoder and decoder ICs that speak ITU-R BT.656 (ADV7390 and TVP5150), an 8Mx16 DRAM for buffering frames, and a Spartan 6 LX9 in the TQFP package.

alex.forencich
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    To add: This solution is much less scary/complicated than it might seem at first sight using datasheets and tutorials and/or forums like this and EEVBlog. But the getting a different screen suggestion is also a very good one :-) – Asmyldof May 21 '15 at 23:08