[aprssig] Dual-use on APRS A/D channels

Thu May 7 16:44:36 EDT 2020

Good points.  But if you look at the raw telemetry plot:
http://www1.findu.com/cgi-bin/tele1.cgi?call=psat3,psat3-1&last=36&param=2&b=1&c=0&label=Current&units=Milliamps&autorange=1

It can be seen that there are two narrow ranges of values that are widely
separated.   So, if one "sees-through" the transitions between the two, they
can still see the two separate trends of values.

I guess this is a rare need and a solution to such a rare need, but making
it a generalized capability in APRS would probably not be practical.  But it
could be possible to include a threshold value say d=+500 parameter to the
EQNS transmission that would indicate this equation applies only to values
above 500 and a d=-500 would indicate the equation applies to only those
counts below the threshold.

I'm not suggesting it become part of the spec, but suggesting that if
someone needed to get just one more (or a few more) channels within the
existing structure, they could use this trick.?

Bob

-----Original Message-----
From: aprssig <aprssig-bounces at lists.tapr.org> On Behalf Of Lynn W
Deffenbaugh (Mr)
Sent: Thursday, May 7, 2020 3:58 PM
To: aprssig at lists.tapr.org
Subject: Re: [aprssig] Dual-use on APRS A/D channels

Ok, that's a cool hack for a web-based display service, but how is that
communicated to lowly APRS client applications that receive the telemetry
and (hopefully) the specified parameter definitions?  Such APRS-using,
telemetry-observing applications would have absolutely no indication that
the 2nd value of the 5 actually has dual definitions depending on some
knowledge (the "pivot" value of 500 coded into the URL in this case) that is
completely outside the communications bandwidth from the station.  Not to
mention the fact that different a, b, and c parameters should be applied
depending on that very unknown value.

So this doesn't so much provide for a generic dual-use of APRS telemetry
channels, but allows for an end-user customized view of APRS telemetry using
out-of-band knowledge which can be communicated to a custom telemetry viewer
at findu.com.

Or is there something I missed in Bob's description and example?  Like maybe
a new telemetry definitions packet that describes the ranges and alternate
equations to use?

Lynn (D) - KJ4ERJ - Author of APRSISCE for Windows Mobile and Win32

On 5/7/2020 12:53 PM, Robert Bruninga wrote:
> Steve Dimse has now made it possible for you to make your 5 channels
> of APRS telemetry dual use (up to 10 channels (or more)) and FINDU
> will properly graph the two (or more) different uses of each channel.
>
> I did this on PSAT3 because the current sensor always outputs a
> positive count between 000-999 but changes a digital bit to show if it
> is positive or negative (Charging or discharging).  So I put in a
> transistor switch on that bit and used it to shift the analog output
> to be 000-500 for load current and 500 to 999 for charge current.  And
> now I can get separate plots for each on FINDU.com.
>
> Thus, by using a toggle on all 5 channels, you could extend your APRS
> Telemetry from 5 sensors to ten and still have at least 0.2% accuracy.
>
> Here is the example of the raw data where values below 500 are to be
> interpreted with one equation (load current) and values above 500 are
> to be for charge current and use a different equation...:
>
> http://www1.findu.com/cgi-bin/tele1.cgi?call=psat3,psat3-1&last=36&par
> am=2&b=1&c=0&label=Current&units=Milliamps&autorange=1
>
> When I add "&below=500" to the URLand  use the right equation,  you
> get the bottom LOAD data for values below 500:
> http://www1.findu.com/cgi-bin/tele1.cgi?call=psat3,psat3-1&last=36&par
> am=2&b=1.67&c=-22.5&label=Load%20(only%20bottom%20points)&units=Millia
> mps&autorange=1&below=500
>
> When I add "&below=-500" (with a minus) to the URL and the right
> equation for this situation, then I get the data points for above 500.
> http://www1.findu.com/cgi-bin/tele1.cgi?call=psat3,psat3-1&last=36&par
> am=2&b=1.635&c=-776&label=Charge%20(only%20top%20points)&units=Milliam
> ps&autorange=1&below=-500
>
> The use of a minus sign to switch "below" to "above" was apparently
> easier to implement than adding a whole new CGI just for "above".
>
> The above plots are on the http://aprs.org/psat3.html  telemetry.
>
> A good example of such use might be the monitoring a battery voltage
> (that rarely changes much) so say it uses values from 000 to 999 to
> represent voltage from 000 to 9.99 volts but never goes below say 6
> volts when the battry is fully discharged, then that same telemetry
> channel can also be used for another sensor that never goes above 600 by
> using the "&below=600"
> CGI parameter.
>
> You can see that you could also add a third sensor for example that
> never goes above 300 (or any other lesser value) by adding another
> plot using "&below=300" (as long as the below 600 sensor never goes
> below 300), etc
>
> Bob, Wb4APR
>
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