Switch between 2 video signals

Hi,

I am trying to use 1 digital pin to switch between 2 video signals, like a selector switch with only 1 camera signal going through at a time. I can make a simple NOT gate to enable only one signal at a time with a NPN transistor. Say pin 7 output to camera 1 and the NOT gate, then output of NOT gate connect to camaera 2. The question is, do I need a special transistor that can handle the frequency of the video signal? Say pin7 connected to the base of a transistor to allow signal through, can I use a general purpose NPN transistor on that?

I do not want the switch to control the power to the camera because most camera will need start up time.

do I need a special transistor that can handle the frequency of the video signal?

No you need a special video frequency multiplexer chip to do this. Something like one of these:- http://uk.farnell.com/jsp/search/browse.jsp?N=2031+203960&Ntk=gensearch&Ntt=video+switch&Ntx=mode+matchallpartial

I wonder if a small reed-relay with change-over contacts would work - some phase distortion due to stray impedances perhaps, but there appear to be 50ohm RF reed relays around, no idea the price though.

Ty for the reply that helps a lot, now I just have to add a negative votage part to my list :smiley:

Also I have a new question:

If the output of AD8184 connected directly to the video input of a 5.8Ghz video transimitter module, do I still need a AD8009 (Op Amp) to buffer its output?

I think the AD8184 will solve my problem, it cost around <£5 which is not too bad and also allow me to add more cameras at later stage.

do I still need a AD8009 (Op Amp) to buffer its output?

It depends on the input impedance of your video transmitter. Most video stuff is 75R so buffers are normally needed.

Do you know a similar chip that comes in a DIP package? SMD is out of my skill range.

Very few DIL chips about now, but how about this one:- http://uk.farnell.com/vishay-siliconix/dg542dj-e3/switch-dual-spdt-video-500mhz-dip/dp/1077117

Yeah, that looks good, tyvm for your help. :D

Say pin7 connected to the base of a transistor to allow signal through, can I use a general purpose NPN transistor on that?

If the video is analog like from simple security cams, then a typical NPN transistor can switch the video. A lot depends on your specific setup.Years ago I made a video switcher for my web cams using NPN transistors and operated it from the pc parallel port.

The camera are simple PAL/NTSC CMOS cam. I will try with NPN transistor first, and see. I have also found a DIP alternative to AD8184 available from RS.

http://uk.rs-online.com/web/p/products/6424008/

When using transistors, care has to be taken with the grounds. I inputted a video capture card, so I let the base current thru the transistor (1ma or less) flow along with the video signal into the capture card.

Hmm sounds like I better use a multiplexer, another question, what happens if I use one of the multiplexer above and not use an op amp on its output?

As best as I remember, the video multiplex chips are not as easy to use as one would think. I also made a mechanical video/audio switcher using a rotary switch from RS and positioned it using a servo.

The old video/audio switchers.

http://web.comporium.net/~shb/switch.htm http://web.comporium.net/~shb/ppswitcher.htm

zoomkat: The old video/audio switchers.

http://web.comporium.net/~shb/switch.htm http://web.comporium.net/~shb/ppswitcher.htm

Interesting implementation there, thx. I think I have found the chip I am looking for and it is available in RS: http://uk.rs-online.com/web/p/analogue-switch-multiplexer/7095484/

It can handle 4 channels and has a built in op amp and it is DIP :D The datasheet is here, it looks easy enough to build: http://uk.rs-online.com/web/p/analogue-switch-multiplexer/7095484/

Never tried the analog multiplex chips like the 4051 and 4061 chips, but they might be quick and easy to use.

OK, from the AD8174ANZ datasheet the example cuits uses 50ohm and 75ohm resistor to terminate. What power rating of resistor should I use say 1/4w, 1/2w ?

OK, from the AD8174ANZ datasheet the example cuits uses 50ohm and 75ohm resistor to terminate. What power rating of resistor should I use say 1/4w, 1/2w ?

An 1/8 watt will probably do.I don't thin video signals carry much current. So you have figured out how you will supply the -5v?

The ICL7660/MAX1044 seems to be able to handle the negative voltage.