It works, although I didn't feel comfortable drawing that much power from
the serial port (10-15mA) for extended periods and having 120VAC that close
to the port, so I redesigned it to pull power from a 24VAC transformer and
uses an opto-isolator to fire a larger relay.  Also, the relay I was using
kept sticking and required a thump or 2 to get it to release once it had
engaged.  I'm using a batch file that sends the results from a ping command
to the serial port only if the ping failed.  The file is set to run every
hour and the 555 holds the relay in for about 5 seconds after the characters
are sent over the serial port.


Barry

----- Original Message -----
From: "Peter Tran" <ltran@NETZERO.NET>
To: <PICLIST@MITVMA.MIT.EDU>
Sent: Monday, March 04, 2002 4:51 PM
Subject: Re: [PIC]: Serial Port Powered WDT


> Please let me know if your design works? I am interesting in this
> application for my DSL at home also. Thanks.
>
> ----- Original Message -----
> From: "Barry Michels" <bmichels@EPIX.NET>
> To: <PICLIST@MITVMA.MIT.EDU>
> Sent: Friday, February 22, 2002 11:52 PM
> Subject: Re: [PIC]: Serial Port Powered WDT
>
>
> > Well, it took 4 hours, one 555, 3 resistors, 2 diodes, 1 cap, a piece of
> > perf board and several inches of solder.  It's alive!  When there's no
> data
> > flowing on the serial port, the relay stays energized (I'm using a
small,
> > low current reed relay).  All it takes is 1 or 2 characters to
de-energize
> > the relay for a few seconds.  I'm going to try it out at the office next
> > week.  I just hope it doesn't burn out the serial port...
> >
> > Thanks for the help
> >
> > Barry
> >
> > ----- Original Message -----
> > From: "Aaron K" <aaron@LUMINUS.CX>
> > To: <PICLIST@MITVMA.MIT.EDU>
> > Sent: Friday, February 22, 2002 6:47 PM
> > Subject: Re: [PIC]: Serial Port Powered WDT
> >
> >
> > > Something that I think would work well and be very low power (and
> simple)
> > > would be to make a small one shot timer out of a 555 (the monostable
> > setup)
> > > thas is triggered by the first RS232 '0' bit in the byte (which would
be
> a
> > > +5 to +17 or so DC). So you could set up the timing so once this '0'
bit
> > is
> > > recieved, it would start the 555 timer triggering the relay. Then,
when
> > ever
> > > you wanted to turn on the relay, you'd just send any byte out (as long
> as
> > it
> > > has a '0' bit in it) on the serial port. You wouldn't need a RS232
> > converter
> > > either, just hook up the RX pin directly to the 555 with a resistor
and
> > > (probably) some protection diodes, similar to the way the PICs do it
on
> > > their pins.
> > >
> > > Aaron
> > >
> > > --
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> > >
> >
> > --
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> >
> >
>
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>

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