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Thread: Dedicated OBD micro controller

  1. #1
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    Dedicated OBD micro controller

    Hi, I want to build a dedicated OBD diag computer using one of the common micros available rather than have a whole PC dedicated to it.
    Im looking at the Parallal Propeller chip as it has a composite video library ready and is very powerfull! I would output it to my indash display that takes aux video in.
    My problem is this...A basic OBDII to serial cable from ebay (14) doesnt do any protocol conversion and i would need to write OBD libs for the micro to decode the information.
    I could use an ELM327 ic, but that in actual fact is just a PIC micro with the protocol conversion already programmed in!
    What I need is enough info to decode the basic iso OBDII data myself without needing the ELM chip.
    If I can do this without the ELM chip, I could publish the code for anybody to put into a Prop chip and have their own diag computer in a chip

    Im no stranger to electronics, coding or micro processors, however I have never dealt with ODBII before. Its specificall the european ISO bus i'm going to work with. Also, I have a Mercedes, so its apparently custom protocol?
    I promise to publish my code for free. Can anybody help me with documents regarding the OBDII protocol and the Merc specifics?

  2. #2
    Variable Bitrate
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    OBD2 document can be purchased here:
    http://engineers.ihs.com/document/ab...QIACAAAAAAAAAA
    What country do you live in, and what modelyear is this Mercedes.
    Is it a petrol or a diesel engine?
    What exactly do you mean by "european ISO bus".

  3. #3
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    I believe the car uses the ISO 9141 OBDII standard, of the three that are possible.
    Its a Diesel A-Class Automatic from 2000.

    I dont have the cash to go purchasing documentation, this project is intended to be zero to little cost, hence me wanting to implement in a single micro controller instead of just buying the ELM chip.
    While for my single use, this is quite a reasonable cost I want to release the design for others to build, and adding things like the ELM ic makes it a lot harder for people to acheive.

    A single IC with composite video out and a OBD connector would be quite a popular project for beginners, I dont think people should have to fit a whole PC in their car or have a Laptop just to get the OBD info.

    Ive bought a cable with ELM 323 for initial work on the project so I can design the basic code, show information etc but really want to interface without this added expense for others.

    Somebody must have worked directly with the OBDII bus other than the ELM designers?

  4. #4
    SuperMod - OBDII GPS Logger forum
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    SAE J1979 is also available directly from SAE for sixty bucks, without having to fill in a form to get purchase information or a sbuscription.

    Gary (-;
    OBDGPSLogger, for logging OBDII and/or GPS data
    OBDSim, an OBDII/ELM327 software simulator
    mp3car forums: obdgpslogger, obdsim

  5. #5
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    Hack A Day

    I rememeber I had read about this on hackaday.com

    May you want this:

    http://hackaday.com/2007/11/07/inexp...d-2-interface/

    or

    http://hackaday.com/2009/05/12/obd-i...-data-logging/



    Mauricio

  6. #6
    What can I say? I like serial. Curiosity's Avatar
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    http://www.obddiag.net/index.html

    Mentioned a long time ago.

    Check out the MCP2515 for CAN interfacing.

    Doh! Beat me to it.

  7. #7
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    Hi, Thanks but ive seen all the software and adaptors that use an elm327 ic.

    I want specificaly to do this without the ELM ic.

    What I need are details on the timings for the OBD ISO 9141 protocol, and if possible some info on the data bytes passed for Mercedes specific commands.

    My goal is to build a single micro computer that has no ELM in it, connects directly to the OBD port and a composite video monitor.
    I am not able to purchase documents as I simply dont have the money. I just had to pay 105 to recover my car from the towing company that stole it from its legal parking place. (yeah, I can dispute it, will they pay the interest on my credit card? pay for the inconvenience of missing my car for days? etc).
    I want to do this to help people that cant get or cant afford the ELM route.
    I will publish the code for anybody to download and the schematic for anybody to build.

  8. #8
    North of the land of Hey Huns
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    You have to pay to play. Chances are if you publich the proprietary Mercedes codes you will get slapped with a Cease and Desist (ever wonder why there's no proprietary info available online?). As for the base 9141 protocol, if you do not want to purchase the document that tells you what this is you will have to do some googling. A quick google search revealed this document: http://archive.evaluationengineering...s/0398auto.htm which may be of some help to you.
    "stop with the REINSTALLS, what do you think we got some lame-o installer!!!" - mitchjs
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  9. #9
    Variable Bitrate
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    Info about OBD2/EOBD can be found here:
    http://en.wikipedia.org/wiki/OBD-II_PIDs
    But realy you should buy the SAE standards (J1979, J2012) or forget about the project.

  10. #10
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    Well I dont want to forget the project, and cant afford the docs atm.
    For now I will build it using my ELM cable and work on the direct obdii later on when the rest is working.

    Thanks for the links people, its all appreciated. Ive found a few bits relating to obdii and will work to see what I can do.
    I have both the elm cable for working on the main project and a level converter only cable for working on decoding obdii.

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