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Sven in Sveden wrote:
>Yes, this is functionally a case for external watchdogs, confirmation LED's
and all the rest of it. It is important that this really will work, and give
an alarm if the button is pressed. I had the idea that the buttons would all
get "called" one at a time and asked for an individual code response
periodically to see that it all works (maybe a safer id=E9a is to inhibit=
 the
PIC under the button as it is pressd, and the lack of a responce is actually
the alarm).
>

Yes, this application sounds like a perfect fit for having the master unit
"polling" the remote units in succession and continuously. This way the
network protocols will be much much simpler than where the remote units
interrupt the main unit, and have to deal with possible bus conflicts.
Also, by polling each remote in sequence, the master can tell immediately
that each and every one is operating correctly.=20

Each remote has onboard RAM so it can store the existence of keypresses=20
until the master gets around to it. Assuming 1200 baud xmssn, ie 120=20
bytes/sec, on the bus, and maybe 10 bytes of exchange with each remote,=20
this system could poll 120 remotes in 10 sec. That should be fast=20
enough for this situation. =20

The remotes could even count the number of keypresses and indicate
the patients who are "yelling" the loudest.
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D


>The problem of supplying the PIC's with power seems still to me as the real
problem. There is no "local power-point". This technology doesn't seem to
have a real standars, such as "singlewire", MicroWire (R) or something. Just
crude experementing with diodes and stuff... Right ?
>


I think you are very correct - there are no stds for this. However,=20
if you run the remote PICs with 32Khz xtals, then each requires only
15 uA to run, and 100 remotes will require only 1.5 mA. A PIC at 32=20
Khz can do 1200 baud RS232 [not 2400 as mentioned on a recent thread].=20
This is why I picked 1200 baud above.=20

Comm link current should only add another 1 mA or so for the xmit=20
channel [only one xmits at a time - 5v/5K], and <=3D 0.1 mA for each=20
receive channel. Therefore, 100 remotes would require about 11.5 mA,=20
and that should be possible to supply on the comm/power channel.=20

Alternatively, you could break the system up into more channels with=20
smaller units - say 10 channels with 10 remotes/channel - and then=20
you need to supply only about 2 mA of current to each. This should be=20
very easy, I would think.

I am including a GIF image of a combined RS232/power channel
arrangement I jinned up a couple of weeks ago. May help with=20
ideas. [note - this ckt will take a little more current than=20
mentioned above].

best regards,
- Dan Michaels
Oricom Technologies
http://www.users.uswest.net/~oricom
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D


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