Little Lifeboat

I’ve made a hell of a lot of progress!

First off, LIN is 12V and it’s pulled low for bytes. The Logic 8 analyzer is 20V~ tolerant, but doesn’t work well over 5V. So, I used a LIN to UART converter board, and BOOM! Data.

Second, I figured out that the microcontroller had BLE so I got curious and downloaded the JP Heater “MyBluee” app and what do you know, the Airxcel Combi is just a rebranded JP Heater, or comes from the same factory JP Heater sources theirs from.

I also noticed the app has built in firmware updating

This gave me the exact name of the LCD controller firmware file. Next, I downloaded the MyBluee app local to my mac, then inspected the binary with ChatGPT and within a few moments, I had the direct download link to the firmware:

Slapping the bin also into ChatGPT and doing some logic analyzer runs, and boom, I have everything I need to document the bus commands!

There is certainly more work to be done and real world testing, but so much has been accomplished.

Next is to use 2x UART to USB to put UART on TTY and sit in the middle of the LIN to capture data and do command injection. Once done, I’ll throw the UART to LIN on an ESP32 and throw it on MQTT for Home Assistant control 🤌🏻