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Composite video switcher

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jghake

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Hello Everybody,

I found this project here and I would like to modify it a little before I build it out and was hoping someone could assist.

I need/want it to only do video and only 2 sources. It would be best if I could use a push button switch that when on it chose one source and when off it chose another. I am hoping to mount this button somewhere easy to press to switch between video feeds. The ultimate purpose is to switch between a front view camera and a rear view backup camera in my truck so it would be best if it could be powered from a 12v accessory line that was only on when the vehicle was running.

I am technically inclined and have soldered before but I don't really know much about creating/reading circuit diagrams but would love to learn.

Hopefully someone out there can find this easy and give me a hand!




EDIT:
This may be exactly what I am looking for. Can anyone provide information on if it will work or not?



-Jghake
 
Last edited:
2 Port Video Switch

Hi,

Some time ago I created a 4 port video switch for a system whereby we also created a RF control unit for a set of temporary traffic lights for a works entrance, there were 4 cameras connected to a 2.4GHZ video transmitter.

Attached is a redrawn cut down version of the 4 port to allow two ports to be switched with a single SPST switch, originally this was done by a micro.

Plus it gave me an excuse to draw something in KiCAD :)

Anyway, this circuit has been built and tested (as a 4 port variant). All I have done is remove two of the ports and connected 'B' of the 4051 to ground rather than another micro input (as it was going to before).

The only thing I haven't shown is the 4051's VCC and GND connections, and decoupling capacitors (0.1uF between VCC + GND) of the IC's.

Hope this helps.

Wilksey
 

Attachments

  • 2 Port Video Switcher.pdf
    23.9 KB · Views: 205
Thanks!

Is there a benefit to doing it this way versus using the 5 pin automotive relay? I want to be sure that I am not going to damage either the cameras or my very expensive head unit in my truck. Ultimately I was hoping to put all of this into a project box and mount a few RCA connectors on the outside of it so I could tuck it away in the dashboard and forget about it. Which way is going to be better?
 
Never tried using an automotive relay to be honest, the circuit wont damage your head unit, I had four quite expensive Bosch cameras attached to this and a AXIS video encoder which at the time was the best part of £500 for the encoder alone! The system was built in 2007 and it is still being used today by the construction company we did it for.

Ultimately you can choose whichever path you want to go down, as for any benefit, I can't comment, the filter on the output gave me the best quality for the video signal, so it doesn't just "switch". I don't know what the contact resistance is on a automotive relay contact, that could affect the signal.

This board sat in a box with 5 BNC Connectors and 4/5 wires going to the control unit, so there is no reason why you can't do the same with 3 RCA's and three wires (and a switch somewhere) You could add the pulldown at the switch input on the board rather than try and put a resistor in the switch itself, if that is what you were thinking?
 
Honestly I didn't have any idea how to accomplish this until I started googling. I've never built my own circuit before other than the 9v powered blinking Christmas tree ornaments in the past. My father-in-law is really knowledgeable about this stuff so I will talk to him as well. I'd like to have the switch separate from the project box so I can choose where I ant to mount each.
 
Well, the ground will be common, all you need to do is take a cable with +12V from a fused spur, i'd suggest ignition live unless you want to power the switcher when the key is in the "off" position, you can get this from your radio harness, don't forget one will be permanent live for backup as well as ignition, so chose the correct one, a 0V / Ground (whichever terminology you wish to use), a "switch" wire (to one side of the switch) and a +5V from the regulator to put to the other side of the switch. The pull down can be inside the box itself and can be hidden away.

You can if you want to be really clever, put two led's near the switch to indicate which one is "active" not necessary, but a nice touch, you can wire the LED's back to back so only one comes on at any one time.
 
A relay will work, but I would suggest a good quality small signal relay, instead of a big automotive power relay. The contact material used for power relays is optimized for power work, but don't do so well with the few milliamps of a video signal. Power relays are designed such that the spark produced when the contacts open under high current actually clean the contacts. Without those sparks, they will tarnish over time.

Personally, I would go with solid state concept. But the circuit shown needs a few tweeks.

1) The DC bias resistors R4 and R5 should hit the input video lines on the 4051 side of the input capacitors.
2) Input resistors R2 and R3 should be 75 ohms to properly terminate a 75 ohm input signal.
3) The op-amp should be set with a gain of 2, and there should be a 75 ohm series resistor feeding the output jack.

Item # 1 is necessary. It will work without the other two changes, but it wouldn't conform to 'standard industry practice.'

But, if this is to be a manually operated switch for vehicle camera, you would probably be fine with just using an SPDT switch directly.
 
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