security cameras - question

[Clare Snyder]

I have a question maybe one of you fine folks would have an answer for. If I have one video monitor and several video cameras - regular hard wired composite video - can I connect say, 3 cameras in parallel and switch power between the three cameras to scan from one camera to the next in sequence? I tried it with 2 backup cameras and no magic smoke came out and they seemed to work just fine (for the couple of minutes I had them connected). I even tried powering both at the same time and the monitor just lost the signal. When I disconnected one, the other came back up on the screen immediately. This would tend to indicate the cameras have tristate outputs? Or at least open collector - when not powered the output is disconnected???

[gfretwell]

I think you answered your own question for the ones you have tried. Whether you can make a blanket statement is still an open question. They do make multiplexors and you might be able to get another card for your DVR to add more cameras. Mine is set up for 8 but I am a card and a plate with more connectors away from 16.

[Snag]

Before I moved up here I had a computer set up with a card from Q-See that would run 4 cams . I could either pull up one cam full screen or all 4 of them at once on a quartered screen . You didn't say what kind of box you have running them ... most DVR setups have multiple inputs with the same features as the card I was using . I could also set that comp up with a static intranet IP and use any other comp in the house to watch the cameras . I don't remember how much control I had over things when viewing from a remote .

[Clare Snyder]

It's a simple monitor - actually a stereo head unit in a vehicle. It is set up for a backup camera. I want to have backup and sife view cameras - selectable (backup comes on in reverse, left with left signal,right with right signal - and backup over-rides signals. Sinnce askingthe question I found another guy on the internet fif basically the same thing - but front and rear cameras. Multiple NTSC Composite cameras can be connected together without harming any of them - and as long as only one is powered at a time they will not "walk over" each other. 2 on at a time produces an ambiguous signal - so apparently I SHOULF be able to do what I was thinking - - - -

[Rod Speed]

In fact even the most basic security systems do it even better, show all the cameras at once on a decent sized screen and allow you to view just one at the time. Dirt cheap to buy.

[gfretwell]

I suppose you could use relays, shielded to isolate the inputs when the camera wasn't active if you were really worried about it. A single

12v n/o reed relay in a metal can with coax connectors on each end should work.