NNTP-Posting-Date: Fri, 17 Jan 2003 12:53:42 -0600
Date: Fri, 17 Jan 2003 12:56:42 -0600
From: gary drummond
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Subject: Re: RS-232 controlled video switch
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Michael Culley wrote:
> Thanks for the reply. I've had a look at the datasheets for these chips and
> the 4558 looks like what I am after. I've still got a couple of questions.
> Can I wire the video signal direct to this chip or do I need some external
> Do I need to supply -5V? If I do, how do I get -5V?
> Thanks again.
> Michael Culley
> "gary drummond" wrote in message
> > Michael Culley wrote:
> > >
> > > > There is a Maxum chip specifically for video switching.
> > > > Little 8 pin DIP does 2 in 1 out.
> > >
> > > Do you have a number?
> > >
> > > --
> > MAX453 2x1
> > MAX454 4x1
> > MAX455 8x1
> > All contain an amp/buffer amp.
> > Gary
You said in your email you had 3 bits for selection, the 4558
Direct-No, terminate with 75 ohms.
The 4558 does have the capability of single Vcc (it says), but it
will be degraded (higher Ron and possible crosstalk).
Read the Grounding and bypassing section for the things to
watch out for, and keep them in mind if you try single Vcc, they
get much more critical, and will cause more crosstalk.
+/-5V supplies (Linear only) can be had as a wall wart lots of
places, but you might find +12, +/-5 cheaper at Jameco, or other
mail order places. Just make sure the current capacity is there,
and pay attention to the analog VS DC ground notes...
I must stress that if you can, do it the right way first, and
save all the headaches and problems you will have trying
bandaids to fix a circuit that doesn't perform.
I am not an engineer, and for some things I have to drag out
the books to learn or "remember" what I was taught many years
ago. Following the sheets, and asking for help using a
reference design, or sample design, and trying to comply with
the notes from the data sheet, will get many more responses
than a jury-rigged design, and in most cases will work the
Drop a line when you get it working.