Adding support for Carchet TPMS

[kesuhm]

Hi, there! I would like to contribute to your project.

I have (mostly) characterized this aftermarket Carchet TPMS sensor. I lost one of my sensors and, instead of buying a replacement external sensor, I would like to install internal sensors. I currently have to remove the hubcaps from my outer back tires to remove the sensors from my inner back tires to add air when the tires are low. It's a headache! Carchet doesn't sell internal TPMS sensors, so I am using a different model. My goal is to intercept the signal from the new internal sensors and relay it to the Carchet monitor in a language that the receiver understands. Here is a short summary of what I've done so far:

I began with Universal Radio Hacker (URH) software. Data collection parameters were as follows: Sensor frequency: 433.92 MHz Sample rate: 2.0 MSps Bandwidth: 2.0 Hz Gain: 125

The modulation is ASK (OOK) and data packets had the following format: aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa [Pause: 897679 samples] aaaaaaaa5956a5a5a6555aaa65959999a5aaaaaa [Pause: 6030 samples] aaaaaaaa5956a5a5a6555aaa65959999a5aaaaaa [Pause: 11176528 samples]

The decoding is Manchester I. After decoding, the packets look like this: 00000000000000000000000000000000000000 0000a9332fc0a84f1000 0000a9332fc0a84f1000

The packets could be detected with rtl_433 (compiled on Windows 7 with CMake and MinGW) using the following settings: rtl_433.exe -X "n=Carchet,m=OOK_MC_ZEROBIT,s=50,l=50,r=1000,invert" -s 1M

Here are some samples on BitBench:

Case 1: Decreasing pressure Case 2: Increasing pressure Case 3: Decreasing then increasing pressure Case 4: Additional learning

I wrote and tested a Carchet decoder file, which I called tpms_carchet.c and attached as a text file. (I have never contributed on GitHub before, so I am not sure who normally adds devices or modifies the rtl_433_devices header file or CMakeLists.txt file when a new device is added.) I am planning to do some additional testing on the flags, but I wanted to share the code before I went any further. Please let me know if you have any questions or if I need to provide anything else. I'll share more on the flags when I get new data.

Thanks! tpms_carchet.txt

[zuckschwerdt]

That looks plausible. We usualy see TPMS with that coding and timing.

You would just add to the include/rtl_433_devices.h and then run ./maintainer_update.py and recompile (and run ./maintainer_update.py again to update the docs).

You also would fork, branch, push your changes, then PR. If it doesn't work we can insert your decoder manually.

[zuckschwerdt]

• you'll need to cleanup indentation: 4 spaces, no tabs.

[kesuhm]

Thanks for the review and instructions. I will do what you recommend once I have a bit (or byte :smiley:) more understanding on the flags. Back soon!

[gdt]

@kesuhm Any progress? It seems like you have a working decoder and it would be great to get it into the code base.

[kesuhm]

Hi, there! I just submitted a PR. The Carchet TPMS sensor is similar to the EezTire-E618 sensor, which popped up in my display this week while I was testing my code from May of 2022. While the sensor data appears to be identical to the EezTire-E618 output, I hope that the PSI and deg F readouts and low battery and inflate flags may be of some use to those running rtl_433.

[zuckschwerdt]

Let's continue this in #2677 now.