APRS Telemetry System
APRS TELEMETRY FORMAT: The on-air packet telemetry format is as follows:
T#sss,111,222,333,444,555,xxxxxxxx where sss is the serial number
followed by the five 3 digit analog
values and the eight binary values.
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.