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'[PICLIST] (PIC) Hospital ward alarm'
2000\10\26@145748 by MEDICINTEKNIK KB

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Hello everyone out there...

I wonder if anyone of you have come across the following:

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, until now, it doesn't matter where the alarm comes from (just wake up the nurse...). 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 idéa is to, for instance, send a code from a 12c508 just inside the button. I suppose powering 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 diode is necessary on the output pin).

One problem is the noice and stray currents induced in the long wires. And --- this "must be fail-safe"

Anyone been in this corridor before?


Sven in Sweden

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2000\10\26@152225 by Arthur Brown

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On a project I seen a few years ago they used MC14025 & MC14027 this was
powered by the cable via 78L05 and the signal transmited like that on a
Guitar power lead, were the suply and sig are on the same wire.

Regards Art.

{Original Message removed}

2000\10\26@153044 by David VanHorn

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I designed a thing like this, (we called it megaplex) back in about 1980,
using 4000 logic.

You can get pretty creative with polarity reversal and pulses.

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2000\10\26@183909 by Gennette, Bruce

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Sounds pretty easy.  Here's a few suggestions -

Each caller should sleep a lot, waking 10 to 20 times a second to test its
flags.
If a flag is set then the PIC attempts to contact the master station.
Collisions will occur, so messages are resent (each time the PIC wakes up
with the flags still set) until they get through and are acknowledged.
If 5 or 6 patients press at the same time there may not be enough power
available, so each PIC needs to store a 'button pressed' state in non
volitile memory before attempting to signal the master.
Each call station then randomly attempts to get through - if a brown out
occurs the PIC gets another small, forced sleep, then when it wakes up it
tries again until it succeeds.
Then it stores a 'call registered' value in the same manner (for the same
reasons).  Now each time it wakes it requests an acknowledgement that a
human has accepted the call.
And finally a 'call acknowledged/answered' tells it to go to its idle state,
waiting for a button press.
If the caller has to light a 'call sent' LED then the LED should only be lit
for a short time each time the PIC wakes (it will appear to be frantically
flickering to patient).
Holding the lit button down for 2 seconds could also initiate a remote
acknowledgment.

These methods should reduce the maximum load in a system to about (2 x
maximum caller load) x (number of callers / (ratio of wake to sleep time));
with a large ratio this can be simplified to 2 x a maximum caller load.

Caller circuit boards should have 8 easy to get at 'cut here' tracks for
setting station ID on-site.  Stations should be given unique manufacturers
serial numbers too, so each reports its current station number setting AND
personal ID in all communications.

With ALL communications initiallized from the callers a reverse polling
system will have to be used to check for failed callers, possibly initiated
manually.  A full system of 256 callers waking up randomly about 20 times a
second should all check in within 30 seconds.  The master can then report
which station numbers are active, for the operator to check against the
installation map (all should report duplicates).

bye.


> {Original Message removed}

2000\10\26@190243 by Christian Dorner

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> The idia is to, for instance, send a code from a 12c508 just inside the
button. I suppose powering 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 diode is necessary on the output pin).

> One problem is the noice and stray currents induced in the long wires.
And --- this "must be fail-safe"

Hi!

I'm working currently on a project (home automation) with a simular problem.
I use 3 wires (the supply is seperate cause i've to drive relays) but here's
my idea to build a simple and stable bus-system, cheap with low part-count
(4 pices for TX and RX):

The Transmitter ist just a Resistor (about 10k) connected from a Portpin of
the PIC to a NPN-Transistor Base (somethink like a BC 337). The Transistor
Collector ist connected to ground. The Transistor Emittor is connected to
the Bus.

The Receiver is simple like the Transmittor Part: A Resitor (about 4,7k) is
connected on the one side to the Bus and the other side to a Zener-Diode
(5,1Volt - to bring the Bus signal to TTL) and to the Portpin of the PIC.
The Zener-Diode is connected to Ground.

The Bus wire is pulled up on every end (maybe on more places) with a
Resistor to the Supply. (+12V in my case)

I think this construction should be work fine even on long wires cause when
there is no signal on the bus the signal on it is high. When a signal will
be transmitted the bus will be thrown to ground. All in all it's somethink
like a modified (brutal?) version of a 20mA Current Loop.
BUT - i've even build this and tried this on my desk (even with long
telephon-wires) and it works fine - no reality test available.

Maybe someone out there has build something like this or similar with
reality expirience on it.

For additional safety you should poll the switches to be shure that every
switch is online.

I hope this helps or give you some inspiration for your project.
Good luck.

cu, Doc ...

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2000\10\27@020549 by R. Monsees

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Maybe you could use these I-buttons or 1-wire-chips from DALLAS Sem.,
the make ID-Chips wich send there unique ID via a 1-wire-bus (+ground,
makes two wires ;-) ) when they are connected to the bus.
let me know if you find a solution !
regards
    Reelf
...
from (just wake up the nurse...). 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 idéa is to, for instance, send a code from a
12c508 just inside the button. I suppose powering this over the twisted
pair, a
>
>...

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2000\10\27@065655 by Andrew Kunz

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part 1 1119 bytes content-type:text/plain; charset=us-ascii

Sven,

I used to work in a similar area of the market, installing TV systems which are
usually attached with the nurse call.

For liability reasons and reliability, it is best to pull the extra wires.  In
the USA, the cost of rewiring with union workers is about half the cost of the
lawyers, let alone any settlements which could result.

Andy










MILTON MEDICINTEKNIK KB <.....milton.medicinteknikKILLspamspam@spam@TELIA.COM> on 10/26/2000 02:33:43
PM

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Subject: (PIC) Hospital ward alarm








Hello everyone out there...

I wonder if anyone of you have come across the following:

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, until now, it
doesn't matter where the alarm comes from (just wake up the nurse...). 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

part 2 628 bytes content-type:text/plain; charset=iso-8859-1
(decoded quoted-printable)


ťa is to, for instance, send a
code from a 12c508 just inside the button. I suppose powering 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 diode is necessary on
the output pin).

One problem is the noice and stray currents induced in the long wires. And ---
this "must be fail-safe"

Anyone been in this corridor before?


Sven in Sweden

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part 3 135 bytes
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2000\10\28@062913 by Dr. Imre Bartfai

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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:

{Quote hidden}

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2000\10\28@170000 by Andy Howard

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Some alternative suggestions:


Have the button operate a relay which latches a light above the bed and/or
door and rings for the nurse.

Have a resistor between each button on the circuit and measure the
resistance (gives wrong answer is more than one button pressed at once -
limited number of buttons in practice).

But those are rather clunky. I really think your best idea is to use Dallas'
1-wire bus with their digital id chips. You can power the id chips from the
bus if I recall correctly.





{Original Message removed}

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