From: engp2254@nusunix1.nus.sg (SOH KAM YUNG)
Subject: Re: Protection of serial (RS232) lines
Organization: National University of Singapore
X-Newsreader: TIN [version 1.1 PL6]
Lines: 39

Martin John Gregory (mgregory@flash.pax.tpa.com.au) wrote:
: I've started to look at some devices doing serial data transmission
: over fairly decent distances in fairly noisy environments, and have
: seen a variety of schemes for protecting the RS232 transceivers (and
: the rest of the circuit) from transients on the serial lines.  I'm
: left wondering what is the best way of doing this?  How necessary is
: it?
: [stuff deleted]
: What is the wisdom on this out there?
: 
: Ta,
: 
: Martin.
: 
: 
From what I know, protection is necessary, esp. if you plan to route
the cables into an unknown environment (out of your control). Things
like accidental shorts between the signal lines and power cables, or
even lightning strikes are very likely and I don't think you like to see
the sight of your computer going up in smoke! [Even ethernet cards are
protected. I've looked at the one in my PC and the connector is
protected by a gas discharge tube!]

{But if you plan to use the serial cables for internal routings (i.e. in
controlled environments), it should be reasonably safe not to have
them.}

Suggestion: look in the RS data book. They have several RS232
transceivers that have overvoltage protection. Among them include the
LT1080, LT1081 and MAX250 and MAX251. The Maxims are suppose to be
electrically isolated ones but still need opto-isolators to work (don't
ask me why. I've never used them before.

Another alternative is an RS232 surge protector. Two are listed in the
RS catalogue. If you need additional info (i.e. stock nos.), just e-mail
me.

Soh Kam Yung,
engp2254@nusunix1.nus.sg