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I am capturing the TPMS sensor transmission in URH, but i am having extremely hard time to decode correctly the signal.

I know exactly what is the data string that my real sensor is transmitting and i also know from the supplier that the sensor uses an Infineon SP37T chip, which transmits up to 10kbit/s. The supplier said they use FSK modulation, but looking the signal seems some phase shifting too. This is the string my sensor sends (in Hex):

54 50 56 2C A7 00 2C 00 0F 2C 00 66 2C 00 20 2C 00 00 2C 00 45 2C 00 FF 2C 00 51 0D 0A 00 0F 00 66 00 20 is the sensor ID. 45 is the temperature and 51 is CRC.

I cannot decode right in URH, probably the many parameters on decoding are not correct.

HERE are some samples i recorded with URH. The string transmitted is the same, but they look slightly different because i was trying different gains, antennas, sample rate and also tried with HackRF and RTL-SDR. I have noticed that the sensor sends 2 different blocks of data, not sure exactly why. For sure it is not a repetition. First may be a preamble(?). Appreciate if someone helps to make the decoding match the known data.

toolic
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Pedro Silva
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  • Just to complement, the sensor IC SP37T uses one of the following encoding: - Manchester - Inverted Manchester - Differential Manchester - Biphase 0 - Biphase 1 - Chip Mode (NRZ) – Pedro Silva Jan 04 '23 at 15:12
  • Have you read the data sheet for the device you mention? – Andy aka Jan 04 '23 at 16:37
  • @Andyaka yes, but it doesn't go down so deep on these encoding/modulation details, unfortunately. I think the key information should be the transmission baud rate so i can determine how many samples per bit and also the encoding type, which is one of the ones i informed above. These modes are taken from SP37T IC datasheet. This is determined by firmware, which i don't have access. Thanks! – Pedro Silva Jan 04 '23 at 18:23

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