Emulating a Schrader TPMS

[David Faulkner]

Hello,

I am trying to emulate a Schrader TPMS sensor and am having a bit of trouble. I started with a real sensor and managed to pick up data from it and got the following:

time      : 2022-11-22 10:46:08
model     : Schrader     type      : TPMS          flags     : 00            ID        : 0C581FB
Pressure  : 2.5 kPa      Temperature: 25 C         Integrity : CRC

So looking at the Schrader payload the hex format should be:

SYNC: F

PREAMBLE: F

FLAG: 00

ID: 0C581FB

PRESSURE: 01

TEMPERATURE: 4B

CRC: 4B

I believe that is the correct decoding, I am not sure about the CRC though. Assuming it is correct, i now try to send this message using the HACKRF ONE in URH tool to emulate it. Problem is when I send the message as stated above RTL_433 does not see it. I dont know if it is not seeing the propper amount of bits (68) or if it is failing the CRC, but im sure its one of those.

My questions are is my decoding of the sent payload correct and if correct, what the easiest way to debug why rtl_433 is rejecting the message sent from the HackRf One?

[Greg Troxel]

David Faulkner <dvfaul...@gmail.com> writes:

> Problem is when I send the message as stated above RTL_433 does not
> see it. I dont know if it is not seeing the propper amount of bits
> (68) or if it is failing the CRC, but im sure its one of those.

It is remarkable that you can be so sure when all you know is that
rtl_433 "does not see" it. I would suggest that
- you start capturing signals and analyzing them
- you place the hackrf one 20m away from the rtl_433 receiver and
configure TX power to say +13 dBm.

[David Faulkner]

When i say rtl_433 "does not see it" i simply meant as a Schrader device, or any supported device for that matter.

Im sure im doing something wrong and am not claiming it is in any way an issue with rtl_433.

As for analyzing the signals, i have and found the following:

When i take a recorded  packet and simply play it back, i can see it on the rtl_433 capture printout.

When i place it in the analyzer and decode it, i am always missing 1 or 2 bits.

I believe it is dropping the either the preamble or sync bits, but i am not sure.

Which is why i asked if my decoding in the known payload above was correct so i can determine which bits are missing.

I did not place the Hackrf that far away, ill try that next.