Telemetry decoding

Describes how to decode data from recieved telemetry. This includes evaluation of temperature, pressure and humidity from measured values or GPS coordinates.

Each frame contains payload consisting of subframes with varying length.

expected payload length: 32

TODO: verification needed, possible documentation bug

expected payload length: 24

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];

expected payload length: 122

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 satelite channel state.

expected payload length: 10

No usefull values available to decipher this frame, have someone something?

ussual content:

0x03 0x03 0x00 0x00 0x00 0x00 0x00 0x00 0x00 0x00

expected payload length: 4

This type of frame probably identifies only padding

• no CRC?
• constant pattern of repeating (0x02 0x00) ?

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)

Consist of sequence of repeated fields with following structure:

Example of calibration data

• Coefficients at rows 1Nx are never chenge.

• http://ams.confex.com/ams/pdfpapers/69226.pdf