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Date:      Fri, 1 Oct 1999 10:18:49 -0700 (PDT)
From:      David Wolfskill <dhw@whistle.com>
To:        freebsd-hardware@freebsd.org
Subject:   Computer-controlled switch?  (Not X10 complexity)
Message-ID:  <199910011718.KAA51184@pau-amma.whistle.com>

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I have an application where I'd like to be able to have a daemon
monitoring a set of conditions, and in response to a certain set of them,
be able to open a circuit, keep it open for a certain length of time
(at least 5 seconds), then close it.  Although there is some room for
choice as to precisely which circuit I use (more on that below, if folks
care), there is no reason to be concerned with anything greater than
usual house wiring, and far less than 0.25 A.  Ideally, the circuit
would merely be a phone line (RJ-11 jacks).

The machine that would, ideally, be doing this is also in physical
proximity to the circuit in question.

I've started looking at the x10 stuff, and it looks interesting and
all... but

* it seems overly complex for the aplication;

* it isn't clear to me how well the x10 signalling will work if a
  device to be controlled is getting its power from a UPS.


Now, I'm certain this is doable.  I'm less certain that it can be done
economically and reasonably safely by someone (me) whose track record
with hardware is... less than stellar.

I would also prefer to be able to control it from, say, a serial port
(by sending ASCII text to it; possibly getting ASCII replies back,
though that's far less critical).


The specific application is to force a re-sync for the Alcatel xDSL 1000
network termination device I have at home.  Every once in a while, it
detects loss of sync and copes appropriately, but then sometimes it
fails to recognize loss of sync, even though it won't pass packets.
If/when that happens (as it did yesterday morning) after I get to work,
the home net is isolated... which rather defeats much of the purpose of
having a 24x7 connection to the Net.

So I figured I could have a daemon pay attention to what's going on
(either try to ping the default router a couple of times every 2 or 3
minutes, or look at the output of "netstat -ni" on the external
interface, and if there was traffic in both ways, go back to sleep;
otherwise, try the ping).  If the daemon decides that corrective action
is appropriate, I'd have it either power-cycle the Alcatel unit or --
preferably -- (effectively) unplug the DSL connection for at least 5
(probably 6, to be safe) seconds, which (empirically) seems to be enough
for the Alcatel unit to realize that Something Is Wrong, then re-connect
it, and let the Alcatel device re-establish sync.

Power-cycling the device would also do it, but would go through its POST
as well, which would slow recovery.  But if I were to adopt this approach,
I could either remove the house current from the "wall-wart"
(transformer/rectifier), or interrupt the 12 VDC output of the
wall-wart.

And yes, I realize that if the Pac*Bell folks are actually doing things
with the outside wires, this may not be useful... but the vast majority
of the outages I've experienced so far would be circumventable via such
an approach.

I'm quite willing to summarize responses sent direct.

Thanks,
david
-- 
David Wolfskill		dhw@whistle.com		UNIX System Administrator
voice: (650) 577-7158	pager: (888) 347-0197	FAX: (650) 372-5915


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