Creating Device to Evesdrop on I2C Bus - Need Guidance

ESPHome
1

First time trying to create and ESP32 device - I’m working to reverse-engineer the output of a water flow meter that’s part of my home filtration system. The meter is on a proprietary and expandable bus speaking I2C. I’ve used a logic analyzer to gather enough data samples to understand the communication but I don’t know how to parse and publish meaningful data in ESPHome.
The meter reports 4 bytes of data from 3 registers - for now, I only want to publish 2 bytes from one read command when they’re non-zero. The communication is repeating and is structured is like this:

Address | Read/Write | Data                | Command?
  0x51         W       0x01, 0x04, 0x00      0xAC
  0x51         R       0x00, /0x00, 0x00/    0x2E
  0x51         W       0x03, 0x00, 0x00      0xAC
  0x51         R       0x00, 0x00, 0x00      0x2E
  0x51         W       0x04, 0x00, 0x00      0xAC
  0x51         R       0x00, 0x00, 0x00      0x2E

The data I want to publish is from the 1st read command (highlighted in green) and only the 2nd and 3rd bytes. I need to avoid publishing for every read because the bus traffic is constant after an hour of idle water flow.

I don’t think I can use the I2C “Component” because it causes the controller to act as a device on the bus and isn’t passive. I found an I2C sniffer that will publish everything it hears up on the bus (esphome_i2c_sniffer) but I’d like to filter the data by address and further-limit publishing to non-zero values as mentioned above. Can someone please help me get started with this?

2

Make a copy of that repo (even just locally). Add the additional constraints you want in the loop() function and only call publish if the conditions match.