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

[Robert Bruninga]

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&param=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&param=2&b=1.67&c=-22.5&label=Load%20(only%20bottom%20points)&units=Milliamps&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&param=2&b=1.635&c=-776&label=Charge%20(only%20top%20points)&units=Milliamps&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