[aprssig] Telemetry question

[Robert Bruninga]

> I had a question about getting telemetry to 
> display in real units.... <snip>
> The basic PARM, UNIT, etc formats are there, but 
> the data seems very specific to sending the data 
> to a single unit.

No, you send the four parameter messges "to the unit's"
callsign, but like everything else in APRS, all clients are
supposed to capture it and then use it when they go to display
the telemetry from that station.   So nothing happens to those
parameters and units when they are received by the telemety
station.  In fact, they are ignored.  The value of the message
that contains these static paramater info is for all the other
clients that receive it on their message traffic page and then
use that data to properly display the telemetry from the
specific telemetry station.

> and whether unused channels can simply be truncated, 

They have to be there for the format to parse correctly.

> I have a Byonics TinyTrak4 and would, as a start, 
> to be able to display the supply voltage and 
> temperature on APRS.FI in real units.

To do that, APRS.FI and any other client has to match the
telemetry stations to the parameters that have been transmitted
to the matching callsign.  THen they can display the fully
paramaterized and scaled telemetry.

> PARM.BATTERY,TEMP,,,,,,,,
> UNIT.VOLTS,DEGC,,,,,,,,
> EQNS.0,.109,0,0,1.96,-273,0,0,0,0,0,0,0,0,0
> BITS.00000000,NOTHING HERE....

Yes, but they have to be sent in message format to the callsign
of the telemetry station.  They are not used there, but then
every client that sees these messages will then know what
Telemetery station to apply these parameters to.

> I know that APRSDos has this built in, but I 
> really don't want to set up yet another program 
> if I can avoid it.

Good luck.  

Bob, WB4APR