Okay, time to start playing with more features...
I've got my OT2 based digipeater sending telemetry, so I can get my
temperature and battery voltage graphed over time.
So we get a sequence of telemetry packets looking something like this:
SPLSTD>APOT21,WIDE2-2:T#127,160,177,250,000,000,00000010
Now to make it look decent, and give readable output, I have to send
some on-air definition sentences.
• A Parameter Name message.
PARM.Temp.,Bat.,,,,,,,,,,,CF
• A Unit/Label message.
UNIT.Deg.,Volts,,,,,,,,,,,NUM
• An Equation Coefficients message.
EQNS.0,1.9608,-273,0,0.07225,0,0,0,0,0,0,0,0,0,0
• A Bit Sense/Project Name message.
BITS.11111111,Spilstead Road Telemetry
If I send an INFO command to the OT2, I get back:
21:00:46 MDT: SPLSTD>APOT21:VE6SRV-12:TEMP:41C VOLT:13.88 RX:15971
FCS:4355 DIGI:41791 CFG1{ai
21:03:22 MDT: SPLSTD>APOT21:T#128,161,178,250,000,000,00000010
My equations are based on information provided in the OT+ user manual
which states:
Temperature: Multiply by 1.9608 for temperature reading in kelvins.
Voltage: Divide by 13.84 for supply voltage reading in volts.
Then, we use the equation used by APRS to calculate the telemetry value:
To obtain the final value of an analog channel, these coefficients are
substituted into the equation:
a x v2 + b x v + c
where v is the raw received analog value.
So, after simplyfying... 161 * 1.9608 + -273 should give me a real
world temp in celcius... 42.68, which looks close to that reported in
the INFO query.
With the voltage, we have to invert the divisor to turn it into a
multiplicand, which gives us 178 * 0.07225, which is 12.86, about 1
volt lower than the value reported in the INFO query. Working
backwards to get 178 to match up with 13.88, that works out to be a
divisor of ~12.8
Is the divisor different on the OT2 than the OT+ Scott?
James
VE6SRV
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