2 Reverse Cameras with Relay and Switch

Hi, I have an alpine Ina-w900 with an alpine reverse camera now. It works well and good but I need to add another camera to my truck bed for gooseneck trailer hooking up. I was thinking if I get the same camera I can splice them together as they are 3 wire cameras and I did put a disconnect on my current one for when my tail gate comes off. I was going to splice the black wires together, and the yellow wires together. Then I was going to use a relay and switch to control which camera was on. I would do 30-existing power for camera red wire, 87a to camera 1 red wire, 87 to camera 2 red wire, 85 to switch, and 86 to ground. This would make camera one my default camera Which would be my reverse camera. Hit the switch and it'd switch to camera 2. Will that be okay for the cameras? I don't want to hurt the cameras by back feeding the video source. Can I use diodes to stop the back feeding? Or is there a better way to do this?

You can't use diodes for the video signal, & there's no power backfeed (if there is, from what?).

I'd use DPDT switching for +V and video.
I'd only use a (DPDT) relay unless there was a valid reason to use one (eg, remote switching).

Switching the video feed isn't a problem? I wasn't sure on that.

And I thought that if one camera was off the video feed would back feed to it. Just didn't want to risk damaging the camera

That's where a DPDT switch (or relay) solves the isolation issues. But one video signal feeding into a "dead" camera should no be a problem; they should be high impedance - ie, voltage without significant current.

Diodes may be okay since the video signal should be all +ve, but you need a fast signal diode for that (I generally assume video signals to require ~6MHz bandwidth as required for oldskool TV etc (~700x400), ie capable of handling at least 6MHz).

But I suspect a mere SPDT that switches +12V power to one or the other camera with their (video) outputs joined would be fine. However, if both are are on simultaneously OR to prevent one (signal or camera) affecting the other, I'd switch the video as well. Hence DPDT switching.   


There are - or were - 50 Ohm & 75 Ohm impedance relays specifically for video & TV signal switching, but it seems most find normal relays do the job - ie, the short distance of any non-impedance matched relay is usually not a big issue... Only if signal bouncing (image ghosting) or noise or interference present a problem would one worry about a specific relay.

You could test-bench - tie both video outputs together and try each camera (each camera's +12V input to +12V battery terminal or power supply; ONE at a time) and see if the picture is okay. Then only an SPDT switch (or relay) is required. I doubt that any (i)video circuitry[/i} or camera damage would result. [ For Pete's sake you other readers & gurus, please interject if you disagree or suspect otherwise!! ]
But to be sure, or allow for simultaneous operation (you may keep both on permanently, or keep the rear camera on for a while after disengaging reverse), I'd use DPDT - ie, switch both the +12V and the video signal. (GND can stay connected.)

I'd consider a something like:

... a mini on-off-on DPDT toggle switch assuming its location was suitable.
Else a similar SPST switch to turn on a DPDT relay if the switch is "remote".

Cheers,
Peter (the oldFart)

How did you mod for this work out? I was thinking 3 cameras... original, one in bed for gooseneck, and final on front.

Instead of putting the camera power on a switch, why not put the video cable on a switch. The cameras don't draw much power anyway. Just get a DPDT switch like this

https://www.parts-express.com/dpdt-slide-switch-1-4-lever--023-668

solder on the wires and switching cameras is as simple as flipping a switch.

I have one of these to toggle between two cameras going to one of my monitors
https://www.parts-express.com/dpdt-mini-toggle-switch--060-338

and one of these to toggle between 4 other cameras going to another monitor (have 2 more inputs but ran out of places to put cameras!)

https://www.amazon.com/Parts-Express-Rotary-Position-Non-Shorting/dp/B005CRLWJ4/ref=pd_sim_sbs_hi_3?ie=UTF8&refRID=1GWX4A4RFAMQV9WBVX0Z