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[wxsig] temperature sensor - substitute DS18B20 for DS18S20?

Ted11 tedlists at hullar.com
Wed Aug 25 07:18:48 UTC 2010


I managed to find a DS18S20 locally, so I went ahead and put that in.  But,
hit a problem.  When I go through the setup, the system recognizes both it
and the AAG anemometer unit temperature sensors.  I select the external
sensor, and I get good temperature data out of it.  However, I lose the wind
direction and speed information from the AAG sensor.  If I go back through
the setup, and select temperature from the AAG unit, I get the wind speed
and direction back, and also the temperature from the internal AAG sensor.
When the external temp sensor is active, the error count increases every
five seconds for both wind speed and direction.  

Thoughts:

1.  Is the DS18S20 somehow in parasitic mode and drawing down too much power
from the bus?  The bus voltage as shown on the LCD is steady at 5.02 V,
however.  

2.  I'm using a 7 V wall wart as the power source for the T238, and the 5V
output of the T238 as as the +5V on the one-wire bus.  For 12 V on the
one-wire bus, I wired in the adapter that came with the AAG kit.  Yes,
probably would have made more sense to use a single adapter for both, but I
wanted to keep the heat down on the T238 regulator.  Would the use of two
wall warts cause this problem?  

3.  Possible software problem?  I doubt this, however, I can't imagine I'm
the only person running the new AAG sensor and an external temperature
sensor, and I didn't see any other reports of this problem in a quick search
of the email archives.  

Any thought appreciated.  A few error codes did show up as APRS comments on
aprs.fi:

0129AFAF0000FF76
0108B9B90000FF76

Ted
KE6ROS



-----Original Message-----
From: wxsig-bounces at tapr.org [mailto:wxsig-bounces at tapr.org] On Behalf Of
William Beals
Sent: Sunday, August 22, 2010 8:56 PM
To: 'TAPR Weather Station SIG Mailing List'
Subject: Re: [wxsig] temperature sensor - substitute DS18B20 for DS18S20?

Ted:

Oops! They are different parts with different family IDs, so it will
definitely not be recognized.  I was out this weekend, let me look at the
DS18B20 a bit closer before you order.

will

-----Original Message-----
From: wxsig-bounces at tapr.org [mailto:wxsig-bounces at tapr.org] On Behalf Of
Ted11
Sent: Saturday, August 21, 2010 7:31 PM
To: 'TAPR Weather Station SIG Mailing List'
Subject: [wxsig] temperature sensor - substitute DS18B20 for DS18S20?

I wanted to add an external temperature sensor to my T238, but mistakenly
bought a DS18B20 instead of a DS18S20.  I figured I would wire it up
anyways, and unsurprisingly, it doesn't work.  On the off chance it should
work, and doesn't because I screwed up somewhere else, I wanted to ask if
anyone has gotten a DS18B20 to talk to the T238+.  

Otherwise, I'll be ordering the right part on Monday!

Ted


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