[Weather] calibration for 1.2a version Bray barometer

[Ernie Oporto]

I can't find any documentation for this unit.  Got it a long time ago when
the 1.1a just went out of production, but before the 2.0 came out.  It was
supposed to be very similar to the final 2.0 design except that this unit is
still limited to 5V.  Anyway, when trying to calibrate it (per instructions
at http://davidbray.org/onewire/baro20.html) I am seeing Vad fluctuate all
over the place as the unit just sits untouched on the bench with just power
and the 1wire.  Below is an example of what I'm seeing.  Hopefully someone
with experience calibrating these units will be able to give me pointers.

I used barocalc2 to give me this output and I set R3 and R4 as requested.
R5 changes, but seems to have no effect on Vad which is fluctuating as
below.
Header TextElev LoBaro HiBaro LoVolts HiVolts R3 R4 wiper to GND LoVin HiVin Gain, 1st stage Gain, 2nd stage Overall Gain V3 (pin 3) Bias, 1st stage Bias, 2nd stage 


C:\EODocs.back\My Files\electronics\ibutton\baro\baroCalibrate>baroCalibrate
4.25 1.25 30.7 28.7

baroCalibrate Version 1.01
Dallas Semiconductor Corporation
Copyright (C) 1992-2001

Port number: 1    Port type: 5
Main driver version: FF IBFS32 V3.22 06/17/05 (IBFS32.DLL)
Sub-driver version, Type5: COMU DS9097U V3.22 06/17/05 (IB97U32.DLL)


Searching for a DS2438..

Found 1-Wire Network Address: 1F000000241B6A26
Is this the barometer's DS2438? y

barometer  Vad    Vdd    tempC   tempF
28.520     0.98   5.01   0.00   32.00
28.834     1.45   5.00   40.69   105.24
28.820     1.43   5.00   40.75   105.35
28.587     1.08   5.00   40.66   105.18
28.660     1.19   5.00   40.78   105.41
28.361     0.74   5.00   40.81   105.46
28.547     1.02   5.00   40.69   105.24
28.694     1.24   5.00   40.66   105.18
28.827     1.44   5.00   40.66   105.18
28.387     0.78   5.00   40.78   105.41
28.667     1.20   5.00   40.66   105.18
28.967     1.65   5.00   40.81   105.46
28.347     0.72   5.00   40.78   105.41
28.794     1.39   5.00   40.75   105.35
28.554     1.03   5.00   40.75   105.35
28.554     1.03   5.00   40.69   105.24
28.540     1.01   5.01   40.75   105.35
28.380     0.77   5.00   40.78   105.41
28.820     1.43   5.00   40.72   105.29
28.340     0.71   5.00   40.81   105.46
28.840     1.46   5.00   40.78   105.41
28.367     0.75   5.00   40.75   105.35
28.361     0.74   5.01   40.72   105.29
28.720     1.28   5.00   40.78   105.41
28.660     1.19   5.01   40.84   105.52
28.520     0.98   5.00   40.81   105.46
28.980     1.67   5.00   40.78   105.41
28.580     1.07   5.00   40.72   105.29
28.420     0.83   5.00   40.81   105.46
28.567     1.05   5.00   40.78   105.41
28.434     0.85   5.00   40.78   105.41
28.974     1.66   5.00   40.81   105.46
28.620     1.13   5.00   40.81   105.46
28.894     1.54   5.00   40.78   105.41
28.347     0.72   5.00   40.75   105.35
28.714     1.27   5.00   40.81   105.46
^C



-- 
Ernie
http://www.shokk.com/blog/
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