Bluetooth + ELM327 + Honda

Some quick notes on a recent project that ended up going nowhere. Mostly for my reference later, when I ask: “Why the heck did I do it that way…?”

    1. Using an HC-05 with and ELM327 Bluetooth module works. For testing this is what I did:
      • I used an old Arduino Leonardo; USB to a notebook and softwareserial to the HC-05.
      • 38400 baud – and I did change the ELM so that there were no baud rate change hijinx after connecting.
      • The command
        AT+PSWD=1234

        works waaaay better as:

        AT+PSWD="1234"
      • Pay attention to timeouts that aren’t obvious. Banging through commands rapid-fire didn’t work. Getting a fresh coffee did – the pairing process timed out, and worked as soon as I came back to the car and power cycled the HC-05.
      • Driving the EN pin on the HC-05 is better than fiddling with that little switch on the PCB. Driving a MOSFET to actually power cycle the entire HC-05 also saved my sanity.
    2. Using the ELM327 with a 2004 Honda Civic was more or less pointless; the OBD-II bus doesn’t get enough interesting data to do what I needed. Here is what the “PID’s supported” bytes decode to – basically speed, rpm, temperatures, and a few odds and ends:
    3. Sniffing the CAN bus via the ELM327 didn’t work – likely not a fault of the ELM, but the bus I needed isn’t on that connector.

I think that wraps it up for this project. The ELM dongle is more useful with a smartphone app, since I can’t see some of the data that I’d need to take it further with an in-car computer. I did end up tinkering with a method of generating LCD menus that was interesting, if a overly complicated, but nothing worth a library at this point. Maybe on a newer car it would be worth it.

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