Hi,
use the iButtons of Dallas for every buttons. Ask the line - say - every
500 msec. BTW Dallas describes how to ask the ID of every buttons which
are on-line.

Regards,
Imre


On Thu, 26 Oct 2000, MILTON MEDICINTEKNIK KB wrote:

> Hello everyone out there...
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> I wonder if anyone of you have come across the following:
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> Presently a "nurse-call alarm" consists of one button in every room in a =
large ward. There is only one twister pair across the whole clinic, as, unt=
il now, it doesn't matter where the alarm comes from (just wake up the nurs=
e...). The new use is an indicator to tell which button was pressed. I don'=
t want to climb around to install new wires everywhere. The id=E9a is to, f=
or instance, send a code from a 12c508 just inside the button. I suppose po=
wering this over the twisted pair, a diode and a buffer capacitor might be =
an approach, and temporarily sink the line with ID data (YES a protection d=
iode is necessary on the output pin).
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> One problem is the noice and stray currents induced in the long wires. An=
d --- this "must be fail-safe"
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> Anyone been in this corridor before?
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> Sven in Sweden
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>=20
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