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info:misc:aprs_telemetry_info_dec_2009

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info:misc:aprs_telemetry_info_dec_2009 [2009/12/14 11:49] – created tomgeeinfo:misc:aprs_telemetry_info_dec_2009 [2009/12/21 21:56] (current) – tomgee
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 Each telemetry value is actually a decimal number between 000 and 255. The user can adjust his sensors to meaningful values, or the telemetry equations can be modified on receipt. Usually just a a simple 10k and 2.4k resistor divider is used on channel 1 to give you battery voltage in tenths. So a reading of 138 would mean 13.8 volts. It is easy to make APRS display any other quadratic telemetry equation too. Each telemetry value is actually a decimal number between 000 and 255. The user can adjust his sensors to meaningful values, or the telemetry equations can be modified on receipt. Usually just a a simple 10k and 2.4k resistor divider is used on channel 1 to give you battery voltage in tenths. So a reading of 138 would mean 13.8 volts. It is easy to make APRS display any other quadratic telemetry equation too.
 +
 +Some source code fragments to achieve this:
 +
 +
 +
 +   void ax25sendASCIIebyte(unsigned short value)
 +   {
 + static char count;
 + if (value > 999) value = 999;
 + count = 0;
 +        // first get the MSD (hundreds)
 + while (value >= 100)
 + {
 + value -= 100;
 + count++;
 + }
 + ax25sendByte(count + 48);
 +        // now, get the middle digit, the tens
 + count = 0;
 + while (value >= 10)
 + {
 + value -= 10;
 + count++;
 + }
 + ax25sendByte(count + 48);
 +        // what's left is the units
 + ax25sendByte(value + 48);
 + return;
 +   }
 +
 +===== TT4 Text Mode =====
 +
 +Yes, you can think of TEXT mode as like KISS mode, but where the TT4
 +handles all the AX.25 UI wrapping.  In TEXT sending, you just pass in
 +the data you want sent, an the TT4 handles all the formatting with
 +callsigns you pre-set.
 +
 +The goal with TEXT mode was to make it look like a normal TNC in
 +converse/monitor mode.  So when you send packets in TEXT mode, you
 +just pass in the string to send, terminated with a carriage return,
 +like this:
 +
 +>Hello
 +
 +When you receive packets in text mode, they look like a monitored packet:
 +
 +N6ABC>APRS,WIDE1-1:>Hello
 +
 +Byon
 +
 +
 +
 +On Sat, Dec 12, 2009 at 10:32 AM, tomgle <tomgle@...> wrote:
 +> I've been trying to find info about the Text mode while I wait for a TT4 to
 +arrive. I understand KISS mode requires protocol formatting with call sign,
 +framing etc and TEXT mode does not. Does this imply that TEXT mode is really a
 +KISS frame where all the protocol wrapping is done under the covers? This
 +therefore may mean that you don't have to worry about callsign ID since it's
 +picking up the callsign info from the TT4 stored variables?  I read a lot of
 +back messages and also the manual but have not come up with an answer. Of course
 +if I had real hardware I would just try it and see what comes out of the device
 +but in the meantime I'm trying to read as much as I can.
 +
info/misc/aprs_telemetry_info_dec_2009.1260809353.txt.gz · Last modified: 2009/12/14 11:49 by tomgee