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ThomasScherrer

the best way to video switch ?

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In all sorts of projects we make, video switching will be needed.

please state prefered partnumbers, why,

and comments about results if you have tested them.

info about available, price, delivery time, minimum order quantity,

and so on is also inportant.

Maxim and Analog makes some.

in the old days 4066 was the only part, but it is slow and bandwidth is a bit too low, and internal resistance critical high, so today we dont use this.

http://www.analog.com/en/prod/0,,768_833_A...DG736%2C00.html

looks good, not tested.

http://www.analog.com/en/prod/0,,768_833_A...DG888%2C00.html

looks good, not testet, video AND audio switch at the same time

also look at ADG884 and ADG836 and

ADG451 4 way

ADG711 4 way better pakage SOIC avail

Edited by ThomasScherrer

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MAX4311, 4-way. There are 2-way and 8-way versions too if I remember well.

Samples available, and all. I've always managed to fuel my needs with them. They worked perfectly with my R/C onboard switch.

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http://www.maxim-ic.com/quick_view2.cfm/qv_pk/1892

or directly to the datasheet:

http://datasheets.maxim-ic.com/en/ds/MAX43...310-MAX4315.pdf

the MAX4311 is 3$ and the ADG712BR is 1$

BUT the MAX4311 is more than just an analog mux,

it also contain a video amplifier with variable gain.

and it have 2 bits select input nice and easy for a microcontroller.

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i've recently managed to make vidswitch on 4066 + one-transistor adapter stage of some sort. I am pretty lame at transistors and electronics stuff so I grabbed it somewhere from the net. I got it working only by pure luck as I mixed two resistors and it turned out it only only works with them connected this way. I connected vidout from canon ixus digicam and panasonic kx-131 to 4066 + both output from 4066 to this one-transistor stage, and the stage output to AVR OSD. And it does work.

And on those tiny cameras we use on planes it doesn't seem to have any noticeable degrading effect to video.

here is a clip (I've just uploaded it so it may be inthe 'processing' status for a while)

Edited by mieczotronix

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Interesting !

Can you post the circuit please ?

Terry

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-AT-mieczotronix: How did you provide the symmetric power supply? The circuit you mentioned, as well as the 4066 needs symmetric PS or biased input signals.

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LOL. Talk about luck! I did the same some time ago, it worked too... because I had a camera that has no DC-coupling cap. Switched to another camera that did wouldn't work.

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LOL. Talk about luck! I did the same some time ago, it worked too... because I had a camera that has no DC-coupling cap. Switched to another camera that did wouldn't work.

That's triple luck in this case. All of three cameras I have (KX-131, Sony HACD 1/3" and Canon TV out) seem to work. BTW.

Do you think my Canon IXUS700 has no decoupling cap on its TV out? That's quite strange, isn't it?

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:blink: Great! :)

In case you consider to modify the circuit, or to add several outputs you might like to use a circuit like the one below. It's actually the default for a simple audio amp stage, but with a little changes, you get a nice video buffer stage with biased output and also variable amplification to adjust the video level.

(Just remove C2, change R4 to 470ohm and replace R2 with a 1k var Resistor. Maybe play around with R1,3,5 by reducing their values, if needed)

I'm using it in my DIY diversity receiver and it's perfect. Just take a Video-suitable

Op-Amp (for example LT1207 or a MAXIM Video Op-Amp).

post-6-1180557684_thumb.png

Edited by Hartwig

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The signal ground here is always 0V. Sorry, I should have been posting a more dedicated schematic.

How about this one? Maybe you need to play around a bit with the values of R1,3,5. But anyway this schematic shows the principle.

If you built the circuit according to that schematic, you will have anice biased output at a DC offset level of roughly 2.5V. Also you are able to adjust the video level in a sensible range so you will end up with a signal level of 1Vpp when correctly terminated with 75ohms.

If you want to use it as an output buffer stage, just add another 470uF Cap in series to Rout.

The 75ohms Resistor on the very right hand side is actually the input of the next device. It works really nice for me. I'm using the LT1207, but you can choose one of your own flavour.

Rin (75ohms) is there to terminate the previous stage which feeds its signal into this Buffer/Amp. In order to get multiple outputs from a sngle video source, just use Rin once, and connect the following circuits (all identical to this one) in parallel at this node, so the overall input impedance stays ~75ohms.

post-6-1180656876_thumb.jpg

Edited by Hartwig

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