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Any 1-wire experts around ???


  • Subject: Any 1-wire experts around ???
  • From: "Kevin" <kw1816@xxxxxxxxxxx>
  • Date: Fri, 20 Jul 2012 20:29:04 -0000

I've had a network of 23 1-wire DS18S20 temperature sensors as well as
a co=
uple of DS2423 counters running for while now, talking to Homeseer through
=
the mcs Temps plugin via a DS9097U serial interface.

It's been OK but I get an increasing error count and the the readings can
b=
e 10-15 mins old before they update again (depending on sensor). They're
co=
nnected using CAT 5e on a linear bus approx 40 metres long (23 temperature
=
sensors and 2 dual counters.)

I've been doing a bit of research into how to optimise the network and
redu=
ce the error count but I'm getting more confused by the conflicting
advice.=
I've variously been advised to:

1: Move to external vs parasitic power. Not a big move, when I installed
th=
e network I used RJ45 sockets with the vdd shunted to the gnd - easy to
rem=
ove. I bought a power injector from Hobby boards at the same time as the
se=
nsors and in true HA style it's sat in a box for the last couple of years.

2: Place a 100-120 ohm resistor between the DQ and the network - not so
eas=
y as it would involve removing each sensor and resoldering the connections.

I've read the Maxim Guidelines for Reliable Long Line 1-Wire=AE Networks
ht=
tp://www.maxim-ic.com/app-notes/index.mvp/id/148 but am still none the
wise=
r.

So any advice - Resistors a good idea or just for for external power ?
Both=
or neither ? anything else ?

Cheers
Kevin W
=20



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