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Old Apr 27, 2012, 08:27 PM
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metalfred's Avatar
Canada, QC
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Need help with video switch components

Hello, newbie here. I am trying to self educate myself and learn more electronic stuff.

I need to design a 3 (or more) channel video switch for my FPV plane. I am trying to design the schema with the rights components.

Here is the basic idea; ATTINY2313 mcu that will trigger 2 switches (Relays?) to route the video signal I want out to the video tx.

My questions are, what components can do this? is it a relay? can it be trigged by the pin of the mcu?

Thanks for help.
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Old Apr 28, 2012, 10:31 AM
"Simplify, then add lightness"
Raleigh,NC
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What you need is called a video multiplexer, usually shortened to video mux. I have used these from Maxim long ago and they worked fine. They have a built in amplifier that doubles the output voltage so you use a 75 ohm resistor in series with the output which with the 75 ohm input to the transmitter gets the voltage back to the proper level.
http://www.maxim-ic.com/datasheet/in...p/id/1892/t/al
Those only come in surface mount packages, but they do have an older part that comes in a DIP package but needs external gain setting resistors.
http://www.maxim-ic.com/datasheet/in...p/id/1565/t/al
Other manufacturers make similar ICs.
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Old Apr 28, 2012, 11:52 AM
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But this can only be done with video muxers? It was so simple in my head but you just complicated everything! hehe
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Old Apr 28, 2012, 01:25 PM
"Simplify, then add lightness"
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You can use the relays like you show, but they will be larger and heavier than the mux.
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Old Apr 28, 2012, 03:00 PM
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ok, I am not sure what they are exactly, can you link a relay that could do what I want?

Does this one will work?
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Old Apr 28, 2012, 04:53 PM
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Relays are heavy and would take some current to drive the coils (usually more than what the MCU can drive directly).

Looking at ebay I found some max454 and max455 that would do the job.

I think you can also use simple CMOS analog mux (4016 Quad Bilateral Switches, 4051 cmos multiplexer/demultiplexer, or alike). these are cheap and available.
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Old Apr 28, 2012, 06:19 PM
"Simplify, then add lightness"
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Quote:
ok, I am not sure what they are exactly, can you link a relay that could do what I want?

Does this one will work?
No, that one has a 12v coil and requires a lot of current. Here is a 5v relay with 1000ohm coil that can be driven directly from a microcontroller. You would also need to add a diode across the coil to keep from destroying the microcontroller. It is only SPST so you would need one for each camera and would need a separate output from the microcontroller for each relay.
http://www.ebay.ca/itm/Wabash-1115-1...item41570597c7

Quote:
I think you can also use simple CMOS analog mux (4016 Quad Bilateral Switches, 4051 cmos multiplexer/demultiplexer, or alike). these are cheap and available.
The problem with the simple transmission gate mux and bilateral switch is their high on resistance. It is usually 100 ohms or more and the inexpensive ones are 1000 ohms or more. You can't drive 75 ohm video directly with them so you need a buffer amplifier after them. The packaged video muxes have the analog mux and buffer amplifier built onto the same chip.
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Old Apr 29, 2012, 10:22 AM
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I have just ordered MAX454 and MAX455 video muxers, I think it is a better solution indeed. Actually I ordered some of the new generation samples (MAX4311 and 4312) 2 months ago but they were surface mount, I didn't know that I needed "DIP" to be able to solder them onto a PCB.
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Old Apr 30, 2012, 08:07 AM
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Here is an update of my design. After some reading, MAX454 chip needs V- so I added a dc-to-dc (MAX1044) converter that will feed it. I am not sure how it is supposed to be interconnected with the MAX454 though, can anyone confirm this plan?

Are you seeing any errors?

Thanks in advance.
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Old Apr 30, 2012, 08:59 AM
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There are low voltage, solid-state relays in 8-SMD or 8-DIP packages. Not sure how they'd handle the signal but there are data sheets available. Look on digi..
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Old Apr 30, 2012, 08:59 AM
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update
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Old Apr 30, 2012, 07:15 PM
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Put a decouple cap (0.01) at each chips V+ supply pin.
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Old Apr 30, 2012, 08:11 PM
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maybe you have friends that used Wii MotionPlus gyro for their MWC, if I2C connected direct to ITG3200 then you can pull onboard LN3005 2x bilateral switches rated 15MHz and is meant to switch video. I've used the switch many times, one chip can mux 3 cameras
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Old May 07, 2012, 12:41 PM
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Take a look at this IC, it's specifically designed as a video switch and is low cost and easy to use: http://search.digikey.com/us/en/prod...MCT-ND/2082110

I'm using it in my homemade OSD.
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Old May 07, 2012, 01:16 PM
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Thanks for help and tips. I have received the MAXIM chips and will be able to try them on the proto board pretty soon.

Diagram looks ok?
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