[OZAPRS] Telemetry on APRS Devices

[Andrew Elwell]

Hi Rob,

On 24 May 2013 21:32, Rob Heyer <vk2xic at yahoo.com.au> wrote:>
> Can any one tell me how to make the Telemetry Numbers means or tel me what
> is th formular is to work it out.

cheat method is to use http://aprs.fi/telemetry/a/VK2XIC-12 and see
what Hessu makes of it :-) but in this case it;s not terribly useful
as...

> They are voltage and temp. but which one is which and what is the number
> in  #Volts and  #Deg C?

With the old-school method of sending telemetry[1] the broadcast is
missing a useful set of stuff that can help:
PARM, UNIT, EQNS -- These are needed to answer your question

for instance the telemetry from Tic Hill is
:T#012,152,174,251,000,000,00000010
::VK6RTH-3 :PARM.Temp,Supply,ADC0,Cnt,HDOP,-,-,-,-,-,-,JP,PR
::VK6RTH-3 :UNIT.DegC,Volt,None,#,HDOP,,,,,,,ON,#
::VK6RTH-3 :EQNS.0,1.9608,-273,0,0.07843,0,0,1,0,0,1,0,0,1,0

(snipped for neatness)

but the example you gave seems to be the base-91 variant[2] packets
are in the format:
:`NLHn>_b/'"4)}|!$&$'X|!w{7!|3
(where the stuff between the pipe symbols '|' is the telemety data)
and the spec still says:
"3.12 The existing method for transmitting coefficients and channel
definitions are not changed by this specification. They can still be
used in conjuction with Base91 Comment Telemetry. While the format only
supports positive integers, negative and decimal values can be displayed
with the help of periodically transmitted coefficients, as before."
... so you still need to broadcast (less frequently though) some
metadata about how to decode it.

So - you can't tell without more info. Sorry if thats not what you
wanted to hear :-)

Andrew


[1] Page 68 of http://www.aprs.org/doc/APRS101.PDF
[2] http://he.fi/doc/aprs-base91-comment-telemetry.txt