Detecting when Camera attached

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Hi all, it's been a while since I last posted but I run into a problem that I need to solve for She Who Must Be Obeyed.  I've installed some rear view cameras on our horse trailer and those connect to our truck with a small waterproof pigtrail.  There is a single camera mounted on the truck tailgate to aid in hitching up, and one on the back of the trailer as a rearview when trailering, and one inside the trailer so she can keep an eye on her dearly beloved.

The camera monitor normally displays a split screen view of the interior and rear view from the trailer when the trailer is connected.  It also has "sense" wires that can be connected to 12V to force the monitor to display a particular camera.  I currently have one of these wires connected to the truck backup lights which cause the hitch camera to display when the truck is put in reverse and that is perfect for hitching up.  Once 12V is removed from the sense wire, the monitor reverts to the normal split screen view.
 

Here is the issue - SWMBO would like the trailer rearview camera to be displayed whenever the trailer is connected, and the truck is in reverse.  So, I somehow need to sense when the trailer rearview camera is drawing power (100ma normally up to 500ma at night [IR LEDs automatically come on in low light]), and actuate a 12V SPDT relay to switch between the two different "sense" wires and the backup light switched 12V source.  I have a small 12V automotive relay I can use for the switching with a coil resistance of 222ohms and a nominal operating current of 53ma, but it would be nice to have a solid state solution however I was unable to locate any double throw solidstate relays.

 

As always, your help is greatly appreciated.

Cheers,

Tom

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Are these "sense lines" logic or power providing signals?  If they are logic signals, why can't you use comparators with open collector (High voltage) outputs? The comparator can monitor the voltage drop ,due to current, on a 0.1 or 0.2 ohm resistor. No relay needed at all.

 

Take a look a this chip

http://www.farnell.com/datasheets/5925.pdf

Or you can roll your own, or look for similiar chips

 

Be sure to include transorbs on all of your signals...Voltage spikes are everywhere in your system.

When in the dark remember-the future looks brighter than ever.   I look forward to being able to predict the future!

Last Edited: Tue. Oct 15, 2019 - 06:20 PM
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avrcandies wrote:

Are these "sense lines" logic or power providing signals?  If they are logic signals, why can't you use comparators with open collector (High voltage) outputs? The comparator can monitor the voltage drop ,due to current, on a 0.1 or 0.2 ohm resistor. No relay needed at all.

I assume they are logic signals, but I don't know for sure.  Documentation just says connect to 12V.  Normally they are connected to the turn signals and backup lights to select the "normal" left, right, or rear camera when turning or backing up.

Cheers,

Tom

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If the camera has other wires for power, then these lines are just signals to monitor various conditions...a comparator will work fine.

 

Take a look a this chip

http://www.farnell.com/datasheets/5925.pdf

Or you can roll your own, or look for similar chips

 

Be sure to include transorbs on all of your signals...Voltage spikes are everywhere in your system.

When in the dark remember-the future looks brighter than ever.   I look forward to being able to predict the future!

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tblough wrote:
SWMBO would like the trailer rearview camera to be displayed whenever the trailer is connected, and the truck is in reverse.

 

If the trailer electrical connection is one of the circular varieties like mine there are only 4 of the 7 terminals used.  Simply allocate two of the unused terminals as a connection 'sense' by placing a jumper across the two terminals in the trailer plug, and then use the corresponding terminals in the socket connected to your circuit to sense the trailer being connected, then use a voltage comparator to sense the reverse lights being on from the trailer connection as well.  In theory this can all be done with a couple 12v relays.

 

Super easy.

 

JIm

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