TPMS sensor support - Sefis M3, Careud, Sykik SRTP300

[ivantichy]

Hello.

spent a few days trying to solve this beast:

Similar can be found as Sefis M3, Careud, Sykik SRTP300

Internally it uses SP400 with 8051 procesor. datasheet

Seems like FKS_PCM with 52us. So far I was not able to find the patterns. Preamble looked similar to Jansite.

I kept it on a table and recorded messages - two are very close to each other (might be small temp change).

Still playing with it however any help is really appreciated.

Bitbench

triq

[ivantichy]

Link to cu files: here

Names correspond to "a", "b", etc. in bitbench comments.

[zuckschwerdt]

These samples are from two sensors, "front" and "rear", right? There don't seem to be enough fixed bits for an ID.
Are the codes in chronological order? Is the first byte that changes maybe a counter?
Best action would be to pressurize the sensor and slowly let the air out. You should get a nice progression of values.
The opening of a Pressure Sprayer (e.g. https://www.amazon.com/dp/B0DJ1Q7W2D/) usually fits sensors.

[ivantichy]

Yes, front and rear.

The “missing” id is weird. Sensors have some number printed on them. I can post it tomorrow.

The order in first part is a,b,c,d…

The part with “x” is in order but some messages might be missing.

Nice tip with the pressure.

[ProfBoc75]

Hi @ivantichy , I have a finding, the CRC is classic CRC-16/XMODEM, poly=0x1021 init=0x0000, without the preamble 0xff and the sync word 0x5a9d, only on the Data values.

Data Layout:

        Preamble ___________________________________ SyncWord  Data _______________   CRC 16
Sample [ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff] [5a 9d] [93 c1 48 f1 e9 14 2c] [51 d5]

But looks like the temp, pressure, id and other flags are mixed into the Data field, not possible to guess for the moment.

[ivantichy]

Thank you @ProfBoc75 for the CRC info. That helped.

As far as I am on vacation with no computer I just played with ChatGPT.

It seems pressure is in b4 and b5. The internal ADC is 13bit only so not sure whether/how they use the last 3LBS which have different values.

I played with constants and reasonable values are: 1psi = 1024LSB and K=60000.

However internal ADC gives absolute pressure and 13bits.