[wxsig] Humidity and Pressure Sensor Support

[William Beals]

Clay:

That is a simple enough question that I am embarassed to say that I don't
(and should) have a complete answer for.  I know the sensors I originally
had and supported, but one thing that has happened over the years is that
other folk have made similar enough sensors that they did not need any
different software support and therefore just worked.  I did not keep good
track of those later sensors.  This has been particularly true for the
Humidity and BP sensors as those have gone through many designs.

For humidity, the T238 was designed to work with the original
Dallas-designed humidity sensor that based on the DS2438 and HIH-3605A.
Several folk have copied that design.

For the Barometric Pressure, the design I worked with was the Bray-Jennings
V3.  This is based on a DS2450 and a Motorola MPX4115A.  This particular
model requires a separate +12V supply.  I know there have been several
designs since that have run from lower voltage supplies, but not sure about
one that is totally bus-powered.  The nature of the Bray-Jennings design is
that all the T238 looks for is a particuar voltage range to represent the
"at sea level" BP.  There is a somewhat tricky calibration process you need
to go through.  As such, the T238 can be fairly well insulated from various
design changes.

This is not giving you specific models--which I know you were looking for.
Based on a previous request I do have a question into AAG about how their
sensor works, but have not heard back yet.

will

-----Original Message-----
From: wxsig-bounces at lists.tapr.org [mailto:wxsig-bounces at lists.tapr.org] On
Behalf Of Clay Cottingham
Sent: Saturday, February 12, 2005 11:01 PM
To: TAPR Weather Station SIG Mailing List
Subject: [wxsig] Humidity and Pressure Sensor Support

Is there a list of supported hardware for the T238 on the site? I couldn't
find one. I am looking at adding the TAI8540A 1-Wire Humidity Module and
TAI8570 1-Wire Pressure Sensor from AAG Electronics. If they are supported,
is there sufficient current from the board to support all of this with the
rain gauge and standard sensors?

Thanks!

Clay



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