typnar

I have two DVRs and want to use a single rs485 cable. Both dvrs are next to each other. I could just tap into the existing wire but I feel resistors or other things might be needed to have this operate properly.

Yes it will be daisy-chaining. I'm using more cameras than my diagrams show and this will give you a better idea. DVR A goes with cameras A# then DVR B control B# cameras. I want the current to flow the way of the green arrows and not back into each others DVR with termination at A-2. I just figured it out, it's a diode that controls or blocks the flow of current to just go in one direction. So adding a diode into the A & B wires just after they leaves the DVR would prevent DVR-A's signal from going into DVR-B and vise versa. The whole purpose of this is to prevent any damage from stray signals going back into the dvrs. Is this something that anyone has experience with using? ( ±80V Fault-Protected, Fail-Safe, 1/4-Unit Load, +3.3V RS-485 Transceiver ) http://www.futurlec.com/Maxim/MAX3430CSApr.shtml

I am not trying to have either DVR be able to control any camera. Each DVR will still handle their own cameras, I'm only trying to share the single wire. Here is a new image to show the way I want it to end up. Also note, by RS485 cable I mean the two + - wire A & B. You will see I want to extend the current wire to cover the extra cameras that were previously attached to another wire. I do know that just attaching it as shown will work but the problem I don't want to happen is the signal gets caught in a loop or the signal gets sent backwards into the dvr. For that is why I'm needing some sort of resistor or isolator to add into the beginning of each DVRS cable so it does not accept a signal backwards.

I don't have a controller, these are two Mace brand DVRs and I'm using the Mace Software to control them. They are all connected. The issue is having to run duplicate cat5 rs485 to control a cameras on a different dvr right next to each other. Isn't there some kind of a resistor or isolator I add to the rs485 line so it doesn't send the signal back into each dvr?

It's not one device used by two dvrs I just want to use the same rs485 cable with different camera id. I have multiple zoom box cameras running on a second floor with 1 wire already ran. here is a outline of what I'm trying to do. So the extra 2 cameras at the top right are next to each other and can just link off one of the existing ones.