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Date:	Wed, 19 Jun 2002 02:07:53 PST7
From:	Peter Skye <pskye@peterskye.com >
Reply-To:	scoug-help@scoug.com
To:	scoug-help@scoug.com
Subject:	SCOUG-Help: Printer switch boxes

Content Type: text/plain

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> Peter Skye wrote:
>
> > this used to drive young TTL designers nuts

Ray Davison wrote:
>
> I guess that depends where you went to school. That
> is not something we were left to find out the hard way.

And after three years of circuit theory we had never once done any
distortion calculations or low-distortion designs. I went to the prof I
considered the best of the lot and said, "well how do you design a
low-distortion amplifier?" His answer: "usually you just hook an
oscilloscope up to it and tweak it until it looks good."

That was when I realized that a college education might get me a job but
wasn't going to make me successful.

> I have four scopes, plus an ignition scope, but I didn't
> need one to determine my 550C would not work with my
> mechanical switch box. In this case "they" were right.

But I want to know *why*. :)

> I have a clock radio I fixed by just hanging
> a ten mic cap across the push button.

Good heavens! 10 uF! I've put some .01 ceramic discs across switches
but you're three orders of magnitude above me.

How quickly could you push that button? I would think the RC would hold
it for a second or more.

> > If you are going to throw the switch while
> > it's carrying data then you ought to at least
> > solder some zeners onto the data lines.
>
> I assume you mean a pair of them back-to-back.

If the signal is +-, then sure. I don't recall what it is for printers;
I thought it was 12 volts but don't know if it's 24vpp or just +12v.

> Peter: What printers do you have that
> work with mechanical switch boxes?

Five LaserJet II's. Two of them have duplexers (they're IID's) and I
have them on one mechanical switch box. I also have a spare box which I
never got around to putting onto the three II's.

But surprise! The spare box is 25-pin connectors -- that's the one I
opened up last night for a looksee. However, I just opened the one I
have in the IID feed and it's Centronics (36-pin). I don't have a
Centronics pinout handy, but pins 19-30 are all connected together and
bypass the switch (they must be ground) while 1-18 and 31-36 (the other
24 wires in a 25-conductor cable) are all switched.

> Why would I want to have to mount
> a switch, with all the cables,

I use mine in an "unusual" way. I have several different Printer
Objects which I print to -- one is for family stuff, one is for
financial, one is for filing, etc. I keep everything "spooled" and only
print when I finally want the stuff. And I only print to one printer.

I switch between the printers to "exercise" them. I bought the second
IID so I'd have a spare, and I bought the second and third II so I'd
have two spares. (I like to have spares.) My on-site printer service
company, Printers Plus, comes and fixes them when they break. And they
told me I shouldn't let them sit idle for *too* long because that would
let the rollers harden. So every once in a while I switch printers with
my cute little inexpensive fun-to-use non-zener non-capacitor-bypassed
mechanical switch box.

- Peter

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