30/10/2000

This type of system exists now on telephone cable to address transducers to
send out the current cable pressure as a frequency on top of the DC voltage.
In this case the DC is only used to supply and drive the transducers.

I think that this suggestion is a bit over the top in this case, and prone
to problems when more than one CCT is in use. Addressing is the way to fly
as indicated, but all that this needs to do is pulse the lines. If a
resistor is used in series, then it can not pull the line fully low. The
master end only then needs to look for large variations in current. This
allows a unit to go faulty (Heaven forbid!) where it pulls the line low
(Shock, horror to such a thought) and still the remaining systems can
operate.
Interrogation could be provided if needed and all that sort of stuff etc
etc......


Dennis




> -----Original Message-----
> From: William Chops Westfield [SMTP:billw@CISCO.COM]
> Sent: Monday, 30 October 2000 12:36
> To:   PICLIST@MITVMA.MIT.EDU
> Subject:      Re: (PIC): Hospital ward alarm. Closing. THANKS !
>
> How about this...
>
> The "buttons" are double-pole switches.  the first pole simply connects a
> moderate value resistor across the two wires which would normally be an
> open circuit.)  This gives you something not much more complicated than
> the current situation, nearly failsafe, and no worse than the current
> scheme at indicating trouble.  Use the second pole of your switch to
> trigger a micro (PIC) to send a signal superimposed upon the wires' DC
> level (as exists due to the resistor across the line.)  This gives you
> more specific location information, at a higher potential rate of failure.
>
> BillW
>
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