Video Multiplexer

[KR2_Diving]

So I have been toying with the idea of having a video multiplexer mounted inside my ROV. My plan at the moment is to have 3 cameras mounted on the ROV. (Forward, Down, Back)

My first thought was to have all 3 feeds go up to the surface and do my multiplexing there, but the more I thought about it, the more I would like to NOT do that!

So i have been doing a bit of research and came up with the following two parts:
NJM2244D
or
LT1204CSW

What I would like to better understand is if it is as simple to use these as it would appear. I am not as strong in electronics as I would like to be. I would like to control which feed is rebroadcast using my Arduino. Is something like this as easy as connecting the Yellow Cable from an RCA connection to one of the inputs, and sending the output to my screen?

Thoughts?

[martinw]

It looks very simple to me, you'll just need 2 digital outputs from your microprocessor to control it.

SW1 SW2 OUTPUT SIGNAL
--L----L------VIN1
--H----L------VIN2
-L/H--H------VIN3

In the old days we just used to use relays, the change in characteristic impedance ....

http://www.bluejeanscable.com/articles/impedance.htm

.... of the signal path for such a short length is really imperceivable, but if you want to maintain the characteristic impedance along the path whilst being able to switch the composite video signals from your cameras, these look like the ICs to do it.

Martin

[kenl]

Hi Ryan,

Did you end up getting one of these and trying it? I like the simplicity and size, compared to the other video switching devices I was looking at. The NJM2244D appeals to me more, but I'm not sure why. I can't find them locally in Aus. so would need to order from international (= slow) but that's OK. I won't be in the water this year!

My biggest decisions at the moment are between this, neutral tether and osd, the tether is at the top of the list, but I do want a rear view camera in case my tether gets tangled.

Regards Ken

[kenl]

I ordered some of These a month ago and just gave one a quick try.

It works fine with 2 video outputs, I couldn't try the 3rd because I don't have one yet, the L/H--H------VIN3 confuses me though, what does L/H mean?

Anyways, it's a bit like talking to myself, answering my own questions, but there ya go.

[rossrov]

Hi Ken.

In logic truth tables, L/H is conventionally shown as an X, meaning that the function doesn't care whether that input/control line is high or low. Also, L for low and H for high is normally shown as O and 1 respectively. If you are only using 2 cameras then ground SW2 and select camera with a high or low on SW1

http://www.datasheets360.com/pdf/3801136086086498160

[kenl]

Thanks Ross,

I worked that out later when I looked at the data sheet a bit more.

What I can't work out, and google isn't helping much is the diagrams on page 5 of the data sheet, I didn't do anything with regards to Capacitors or resistors, just connected directly to the pin.

Do I have a Clamp Type input?

Cheers Ken

[rossrov]

No worries. Clamping and the top diagram on page 5 refers to "video DC level restoration". Google that term for further explanation if required.

Depends on the "DC level" coming out of your camera as to whether you need to use the capacitor or not. Personally, I'd just include the components in the top diagram on the inputs with cameras connected and the lower diagram on the other input, just to be safe. Cannot do any harm because the datasheet says that clamping, which is the same as DC level restoration, is done inside the chip.

Clamping means that the lower edge of the video waveform is held or clamped at a specific voltage. This is required if the camera signal is AC-coupled (say by a series capacitor) at any point. The AC coupling removes any DC offset or level from the video signal.

AC coupling a good idea where power supplies, especially grounds, may be less than ideal, such as in a ROV. The capacitor in the diagram does the AC coupling.

All this ROV talk has got me working on my Sonar again. Inspired! Cheers

[KR2_Diving]

Problem solved! Forgot i had started this thread!

Here is the solution I came up with!
viewtopic.php?f=4&t=1471