4 channel video mux for robotics project

Hello guys,
Posted this to the sci.electronics forum as well, so some of you may have seen it already.
I am building a medium size robot that will have up to 4 video sources
that I want to be able to control. The best thing I have found so far has been the "X-QVC-EM" engineering module from www.xavien.com . I have 2 questions:
1. Has anybody used this before, and if so how well does it work? The price is really good, I have seen similar units for alot more money, but you never know.
2. Anyone have any other ideas or recommendations? I need 4 video inputs that are 75 ohms, I want to be able to choose which source is displayed on the screen, and I want simple TTL control.
Thanks guys.
Carl.
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Hi Carl,
I don't have any experience with this module, but I did build a very simple video multiplexer myself. It really depends on your requirements, but if the only thing you require is the functionality of a switch between multiple video sources, without the need to synchronize line & field sync etc. then you might be able to use the same circuit as I used. It consists of emitter followers, one per video source, with their outputs wired together. The inputs are AC coupled to the video sources, and the DC level is controlled through a resistor from digital control lines. There should be only digital control high, which results in that video being transfered to the output. The other emitter followers will have their base-emitter junction reverse biased and are therefore reasonably well isolated. Not a high-performance solution, and I didn't even measure the isolation, but judging from the picture it should be at least 50dB.
I hope this explanation makes sense. If it doesn't, but you are interested in the circuit, please let me know and I will try to give a better explanation and/or send you a schematic. Good luck with your project!
Best regards,
Peter

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