[aprssig] Expanded APRS telemetry to 10 or 15 channels?

Robert Bruninga bruninga at usna.edu
Thu Apr 2 18:04:24 EDT 2020

I haved ignored the 0-255 telemetry spec ever since Kantronics and other
TNC's allowed 0-999 for over a decade.  The limit in the spec was simply to
keep the field to 3 digits each and since up to 999 still fits Im just fine
with that.

Not easy to chage SSID from an external circuit.  Whereas a simple 555
timer chip oronebit output from a processor can toggle back and forth the
extra bank of inputs.  Anyway, just a useful kludge that is backwards

On Thu, Apr 2, 2020 at 4:35 PM spam8mybrain <spam8mybrain at yahoo.com> wrote:

> Isn't that a violation of the original spec saying the values have to be
> in the range 0 to 255 (and be integers)? Or are you talking about the
> values after applying the quadratic coefficients? If so, you still only
> have one set of coefficients for the overloaded channel.
> Wouldn't it be easier to use a second SSID value for the port, so you
> could transmit a completely separate set of values, coefficients, labels,
> etc., under the callsign and second SSID?
> Alternatively, use the !DAO! encoded telemetry in the position report as
> independent of the original format telemetry message.
> Just an idea.
> Andrew, KA2DDO
> -------- Original message --------
> From: Robert Bruninga <bruninga at usna.edu>
> Date: 4/2/20 14:37 (GMT-05:00)
> To: TAPR APRS Mailing List <aprssig at lists.tapr.org>
> Subject: [aprssig] Expanded APRS telemetry to 10 or 15 channels?
> Expanding APRS telemetry from 5 to ten, 15 or 20 channels and still
> remaining within the protocol...
> On PSAT3, I needed 6 A/D inputs instead of the standard 5, so I used two
> inputs on channel 2.  If the count is above 500 then it means one thing,
> and if it is below 500 it means another.  On receipt, I can choose one
> telemetry equation or the other depending on the value above or below 500.
> This means you could double the 5 channels to 10 if you used 500 as the
> dividing line.  Or you could have 15 channels if you restricted one input
> from 0 to 333 and the next between 333 and 666 and the last between 666 and
> 999.  You can make the transition points be anything that matches the
> resolution of your sensors, because the thresholds would be part of the
> decoding equation.  Even if you used four ranges, your precision (from
> 0-250) is still better than a half percent!
> Wow, I wish I had thought of this on my earlier PSATs. Having ten or 15
> channels of A/D telemetry while still using the standard APRS protocol
> would have been useful.
> On the sensor side, you simply switch in bias resistors on each of the
> two, three, or four sensors per input channel.  Think of it as bank
> switching the 5 channels...
> If anyone has use for this trick, let me know.  Steve Dimse is looking at
> building it into FINDU for trivial plotting... if/when he finds he time...
> bob
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