project:weathersonde:telemetry_decoding
Table of Contents
Telemetry decoding
Describes how to decode data from recieved telemetry. This includes evaluation of temperature, pressure and humidity from measured values or GPS coordinates.
FRAME_PAYLOAD_DATA structure
Each frame contains payload consisting of subframes with varying length.
SUBFRAME structure
| offset (B) | lenght (B) | name | content |
|---|---|---|---|
| 0 | 1 | SUBFRAME_TYPE | Type of subframe ? |
| 1 | 1 | SUBFRAME_LEN | Length of subframe payload |
| 2 | 2*SUBFRAME_LEN | SUBFRAME_PAYLOAD | subframe payload |
| 2*SUBFRAME_LEN+2 | 2 | SUBFRAME_CRC | CRC 16 of subframe payload, polynom = 0x11021 (0x1021 withought leadeing 1) |
Known subframe types
| SUBFRAME_TYPE | description |
|---|---|
| 0x65 | Calibration and Configuration fragment |
| 0x69 | Measurement data |
| 0x67 | GPS data |
| 0x68 | RADAC (radiation measurement) / O3 (ozone) |
| 0xff | padding ? |
Calibration subframe payload (0x65)
expected payload length: 32
| offset (B) | lenght (B) | name | content | description |
|---|---|---|---|---|
| 0 | 2 | CALIB_FR_NUM | uint16 | frame number, (starts from 1) |
| 2 | 10 | CALIB_ID | string | 0x20 0x20 + sonde ID (same as on cover) |
| 12 | 1 | CALIB_STATE_0 | uint8 | 0 - OK; 0x08/0x0A - battery low / battery low, powe off countdown running? |
| 13 | 1 | CALIB_STATE_1 | uint8 | see table bellow |
| 14 | 1 | CALIB_UNKNOWN_0 | 0x00 | ??? |
| 15 | 1 | CALIB_FRAG_NUM | unit8 | callibration and configuration fragment number |
| 16 | 16 | CALIB_FRAG_DATA | bytes | calibration and configuration data fragment |
STATE_1
TODO: verification needed, possible documentation bug
| bit offset | description |
|---|---|
| (LSB) 0 | start detected (set at the same time as bit 5) |
| 1 | ??? |
| 2 | humidity sensor heating: 0 = off, 1 = on |
| 3 | humidity sensor for measurement: 0 = U1 (CH2), 1 = U2 (CH3) |
| 4 | set to 1 when current drown from battery is increased by 50mA |
| 5 | start detected (set at the same time as bit 1) |
| 6 | ??? |
| (MSB) 7 | ??? |
Measurement subframe payload (0x69)
expected payload length: 24
| offset (B) | lenght (B) | content | name | description |
|---|---|---|---|---|
| 0 | 3 | int24 | MEAS_T | Temperature sensor (wire at end of stick) |
| 3 | 3 | int24 | MEAS_U1 | Humidity (remoter to sonde) |
| 6 | 3 | int24 | MEAS_U2 | Humidity (closer to sonde) |
| 9 | 3 | int24 | MEAS_REF1 | reference upper bound, increase with temperature (or vice versa, TODO) |
| 12 | 3 | int24 | MEAS_REF2 | reference upper bound, decrease with temperature (or vice versa, TODO) |
| 15 | 3 | int24 | MEAS_P | Pressure |
| 18 | 3 | int24 | MEAS_REF3 | reference lower bound |
| 21 | 3 | int24 | MEAS_REF4 | reference lower bound |
ref = (MEAS_REF3 + MEAS_REF4) / 2;
p_rel = 1.0 / ((MEAS_P - ref) / (MEAS_REF1 - ref) - 0.0655) * 0.9053 + 0.08778;
# pressure in hPa
P = p_rel * ((((CALIB_COEFF[15] * p_rel + CALIB_COEFF[14]) * p_rel + CALIB_COEFF[13]) * p_rel + CALIB_COEFF[12]) * p_rel + CALIB_COEFF[11]) + CALIB_COEFF[10];
ref4 = MEAS_REF2 - ref;
u1_rel = 1.0 / ((MEAS_U1 - ref) / ref4);
u2_rel = 1.0 / ((MEAS_U2 - ref) / ref4);
# humidity
U1 = (
(u1_rel * CALIB_COEFF[43] + CALIB_COEFF[42]) * \
u1_rel + CALIB_COEFF[41]) * u1_rel + ALIB_COEFF[40];
U2 = (
(u2_rel * CALIB_COEFF[53] + CALIB_COEFF[52]) * \
u2_rel + CALIB_COEFF[51]) * u2_rel + CALIB_COEFF[50];
U = max(U1, U2)
rt = (1.0 / (CALIB_COEFF[37] - 1.0) + 17.99418) * \
0.079298 / (((MEAS_T - ref) / ref4) - 0.15791);
# temperature °C
T = ((((
rt * CALIB_COEFF[35] + \
CALIB_COEFF[34]) * rt + \
CALIB_COEFF[33]) * rt + \
CALIB_COEFF[32]) * rt + \
CALIB_COEFF[31]) * rt + \
CALIB_COEFF[30];
GPS subframe payload (0x67)
expected payload length: 122
| offset (B) | lenght (B) | content | description |
|---|---|---|---|
| 0 | 4 | GPS_TIME (int32) | GPS time - ms from week start |
| 4 | 2 | GPS_BLOB_0 | ???, 4*4 bits |
| 6 | 8 | GPS_PRN | PRN for each tracked satelite |
| 14 | 12 | GPS_STAT_1 | signal strength, fix status … |
| 26 | 96 | GPS_DATA_1 | doppler, pseudorange, … |
GPS_PRN
List of pseudorange sequence number for each recieving satelite, 0 == no satelite.
12*5 bit - PRN number (x - unused ?)
11100000 x2222211 44433333 x5555544 77766666 x8888877 AAA99999 xBBBBBAA
GPS_STAT_1
GPS satelite channel state.
| offset (b) | length (b) | description |
|---|---|---|
| 0 | 4 (int4) | signal strength or fix quallity, 0xf == NaN / no signal |
| 4 | 1 | time fix - set to 1 when time is succesfully obtained from subframe |
| 5 | 1 | pseudorange fix ??? - pseudorange fix is correlated to time ? |
| 6 | 1 | pseudorange fix ??? (not corelated to time ?) |
| 7 | 1 | signal tracking - some signal found at certain frequency |
GPS_DATA_1
| offset (B) | length (B) | type | description |
|---|---|---|---|
| 0 | 4 | int32/fract32 ? | value in range < -2e6, 0x1400000 ), pseudorange in metters?, 0x7FFFxxxx == NAN |
| 4 | 3 | int24/fract24 ? | some number, might be signed, not sure, doppler shift? |
| 7 | 1 | ??? | number, min/max: < -38, 39 > usually -5..10 |
RADAC / O3 (radiation and ozone measurement) (0x68)
expected payload length: 10
No usefull values available to decipher this frame, have someone something?
| offset (B) | length (B) | description |
|---|---|---|
| 0 | 10 | ??? |
ussual content:
0x03 0x03 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00
Padding subframe (0xff)
expected payload length: 4
This type of frame probably identifies only padding
- no CRC?
- constant pattern of repeating (0x02 0x00) ?
Configuration and calibration
Calibration data are composed from fragments send in first subframe. Calibration data block is 512B long. Content is identical with data from EEPROM.
- there should be somewhere date/time (GPS send only seconds offset from start of week)
| offset (B) | lenght (B) | content | description |
|---|---|---|---|
| 0 | 2 | ??? | ??? (checksum?) |
| 2 | 2 | unit16 | downlik frequency: f = (400E6 + 10E3*value) Hz upper limit is around 423MHz (value = 0x08FC) |
| 4 | 2 | uint16 | always 0xffff - kill timmer ? |
| 6 | 2 | int16 | always 0x0100 - set transmit power to full ? |
| ??? | |||
| 22 | 10 | string | probe ID (same as printed on conver, starts with 0x20 0x20) |
| ??? | |||
| 64 | 5*x | CALIB_COEFF | calibration coefficients table |
CALIB_COEFF
Consist of sequence of repeated fields with following structure:
| offset (B) | lenght (B) | context | description |
|---|---|---|---|
| 0 | 1 | uint8 | calibration constant index |
| 4 | 4 | float32 | calibration constant value |
Example of calibration data
| coefficient index row/col (x) | 0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 |
|---|---|---|---|---|---|---|---|---|
| 1x | -366.026 | -43.9063 | 393.234 | -131.314 | 25.6268 | -2.02341 | 0.96 | |
| 2x | -803.34 | 363.815 | 317.784 | 127.429 | 0.96 | |||
| 3x | -187.802 | 89.6416 | -26.9122 | 9.15022 | -1.45707 | 0.0868068 | 0.849488 | |
| 4x (humidity 1) | -1223.17 | 3548.18 | -2646.42 | 588.217 | 0.96 | |||
| 5x (humidity 2) | -1198.04 | 3497.31 | -2611.15 | 580.153 | 0.96 | |||
| 6x | 0.0318379 | 0.0374458 | -0.0433925 0.00630527 | |||||
| 7x | -0.000132316 | 0.000414854 | -0.000402439 6.31402e-05 | |||||
| 8x | -2.04505e-06 | 1.5662e-067.05777e-07 | ||||||
| 11x | 0.5227 | -0.0284 | 0.000286 | 8.97e-07 | -1.26e-09 | |||
| 12x | 1.07573 | -0.204 | 0.009009 | -5.83e-05 | -1.04e-06 | |||
| 13x | 0.5227 | -0.0284 | 0.000286 | 8.97e-07 | -1.26e-09 | |||
| 14x | 1.07573 | -0.204 | 0.009009 | -5.83e-05 | -1.04e-06 | |||
| 15x | 4.75029e-06-5.47494e-08 4.851e-10 -1.736e-12 | 0.7 | ||||||
| 16x | 0.7 |
- Coefficients at rows 1Nx are never chenge.
related links
project/weathersonde/telemetry_decoding.txt · Last modified: 2017/02/19 16:58 by pinky