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[aprssig] TT4 or OT2 telemetry

Robert Bruninga bruninga at usna.edu
Thu Jun 26 20:51:49 UTC 2008


> I was wondering if there is a good discussion about 
> transmitting the [APRS telemetry] equations data so 
> you get real units on FINDU or other servers?

Yes, FINDU has that built in.  That is the beauty of using the
APRS standard Telemetry formats.  Full display is supposed to be
done for you in the client programs, but I am not sure any
others but APRSdos decode the on-air units.  But FINDU does not
have to decode the parameters and units off-the-air, since you
just put the units into the URL and FINDU then gives you plots
with fully decoded and scaled values.  

This web page plots the 5 telemetry values for the KPC-3+ in the
attic of my dad's house.  Look at the SOURCE of this web page:

http://www.ew.usna.edu/~bruninga/wb4apr-15.html

For example.  The first IMAGE plot which is of the outside
termperature at my dad's house is given by this URL:

<img
src="http://www2.findu.com/cgi-bin/tele1.cgi?call=WB4APR-15&last
=760
&param=1&a=-.00024&b=0.635&c=-1.5&label=Outdoor
Temperature&units=deg-F&range=20 100">

Notice The parameters in the URL:
CALL=WB4APR-15  (the TNC callsign)
LAST=760        (gives the last 31 days
PARM=1          (for the 1st of the 5 parameters
A=-.00024       (The A coeficinent
B=0.635         (the B coeficient
C=-1.5          (the c coeficient
LABEL= Outdoor Temperature  (the label for the chart)
UNITS=Deg-F     (the Units for the chart
RANGE=20 100    (the SCALE to be used.

THE A, B, C coeficients are for the quadratic equation AX^2 + BX
+ C that match your data.  This lets you use nonlinear sensors
such as thermisters for your temperature sensors.  Most other
equatainos are much simpler. 

Bob, WB4APR

> In looking I find that functionality is built into 
> Bob's APRSDos, and I came across a couple of old 
> dedicated hardware units.  However, is there a general
> discussion of how to do this for something like a TT4 with 
> other software?
> The conversion equations are no problem, just how to 
> upload them.  I normally use UI-VIEW32 for over the air APRS.

> Alan
> WA4SCA





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