How to switch between video inputs

[The Master]

Does this make things more clear?

Perfectly!

I think i was going wrong because to me "COM" means serial. OK, i know it should be "COMM" but lots of people seem to miss off the last M. It does make perfect sense now since there are 3 address pins (2 states each) and 2^3=8 (8 inputs).

It didnt help having pins labeled "in/out" either. Just a small question on these, does that mean i could use this chip the oposite way? (1 input and 8 switched outputs)

I like the definition of "X" in the datasheet :P "Don't care"

I should have realised how it worked before because when i was at school i actually use a chip that does pretty much the same thing but it was only for LEDs.

One last question. Would i be right in saying that the grounds on the video inputs/outputs should all be connected to each other but *not* to the chip. Then the signal wires go into the correct chip pins

[sinoteq]

Yes, you can connect one camera and eight TV and run it backwards so to speak, that is why I said 4051 is MUX/DEMUX. I would connect all GND to the same place to make sure you get the same potential on all cameras this also includes GND to the PIC and 4051.

[The Master]

Ok, Thanx for the info! Now if only i could find somewhere that sells the correct SCART sockets

[The Master]

Ive just been looking at the datasheet again and ive noticed another pin called "VEE". What does that do? The datasheet doesnt seem to mention it so i assume its another one of those basic things i should have been taught in school

[mister_e]

Vee have to be tied to GND or V- if you're using bipolar signal.

[Darrel Taylor]

If you're going to use the 4051, you will need a video amp after it.

I actually tried it once. And was NOT happy with the results.
Like sinoteq said, the ON resistance is too high.
With a 1V p-p signal, I ended up with .8v p-p. Picture gets darker, and sync isn't great either.
Not to mention the Cross-Talk, ... really bad.

Maxim, has some very nice analog multiplexors and cross-point switches. Many are even less than 1 ohm ON resistance. No Amp required.

http://www.maxim-ic.com/products/switches/

.

[The Master]

If VEE needs to be connected to GND then why isnt it connected inside the chip?

I dont really want to use any extra components (especially a video amp) so ill have a look at that link. I dont think it would matter too much because these are only little £12 cameras and are black and white but i was planning to have my PC and skybox plug into this circuit too and i do want the best possible picture for those.

Im sure i saw "low resistance" in the datasheet somewhere but maybe dropping 20% is classed as "low". I suppose i could always put a resistor in the middle of a wire to test how the picture would look before buying any chips. Im sure the datasheet would specify how much resistance there is