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Thread: sample for in-car OBDII output on 20x4

  1. #11
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    no, see my above post on how to calculate it though.
    IN DEVELOPMENT -- '96 Mustang, lilliput with PII/450 laptop, custom DC-DC power supply, 60GB; Garmin GPS; 802.11g; compact keyboard, small graphical LCDs, OBDII.

  2. #12
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    my god, you my friend have completed my senior design project, sort of..

    but yeah, I wanted to take a 20x4 lcd and interface it with obdII on a GM truck, to display information..

    does your setup use a computer? or is it just wired up to the connector itself..

    please more info!

    Thanks!

    its been awhile since I've been around here, but I think im gonna have to get back into this.. my 95 blazer has one of the first obdII systems.. computer in the engine comparment, and obdII connector under the dash, hopefully this will work, or else ill be force to work on the pops blazer.

  3. #13
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    yeah I know that I could get a lot of course credit for all of this stuff that I'm doing

    It's interfaced via a computer but I'm actually considering changing around my setup... I'll let you guys know more once I do!
    IN DEVELOPMENT -- '96 Mustang, lilliput with PII/450 laptop, custom DC-DC power supply, 60GB; Garmin GPS; 802.11g; compact keyboard, small graphical LCDs, OBDII.

  4. #14
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    Dont mean to sound stupid (but im starting to think thats gonna be unaviodable). But where exactly are yougetting the information from? Are you interfacing to the cars management computer or some other device?

    You all talk about the OBCII or something like that, whats that all about. This porject sounds really good, and something I could do easily with my background and programming experiance. But I've got no starting points here.

    Give me a lead and a few weeks and I'll show you hows its done

    Cheers,
    Mik.
    The box said Windows 9x or better.. so I installed Linux

    There are 10 kinds of people in the world those who understand binary and those who don't.

  5. #15
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    OBDII is "OnBoard Diagnostics version 2"

    It's an interface to the car's ECU (engine control unit aka ECM engine control module) which is the onboard computer. This port allows you to connect to that computer to query information from it, mainly designed for diagnostics assistance. The original OBD ports were ad-hoc standards designed by manufacturers to decrease the amount of time that it took to repair a car because of the growing complexity in the onboard computers. OBDII became a standard due mainly in part to California and their environmental laws... search for OBDII on google and you'll find a few thousand links, all that you ever wanted to know.

    what do you want to know about it?
    IN DEVELOPMENT -- '96 Mustang, lilliput with PII/450 laptop, custom DC-DC power supply, 60GB; Garmin GPS; 802.11g; compact keyboard, small graphical LCDs, OBDII.

  6. #16
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    Telek,

    For mode 3/4 requests, I used the ELM322 datasheet as a guide. That should give you enough info to read/clear the troublecodes.

    They don't provide a list of troublecodes, though. I used a Haynes manual for that, but there are more complete lists of them online. (I don't remember the link at the moment)

    Your method of calculating distance based on speed/time seems feasible (I should've thought of that). The margin of error should be within reason as long as the car's speed is polled often enough.

    The other stuff is kind of frustrating...knowing that the data is buried somewhere in the ECM, but not having the foggiest idea how to get at it.

    On scantool.net's software page they mention that they'll be adding support for more real-time sensors. Hopefully, when it's ready, we'll be able to get some ideas from their source code.

  7. #17
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    I've been making some progress but I don't know how to get this data that I've found the info for... I see however that there are counters for

    Code:
    49   RUNNING TOTAL OF FUEL DELIVERED (MSB)   
    50   RUNNING TOTAL OF FUEL DELIVERED (LSB) usec = ([n49] x 256 + [n50])*15.26 
          
    51   RUNNING TOTAL OF DISTANCE TRAVELED Miles = n/2000 
    52   ENGINE RUNNING TIME IN SECONDS (MSB)   
    53   ENGINE RUNNING TIME IN SECONDS (LSB) Sec's = ([n52] x 256 + [n53])
    which pretty much gives the exact overall fuel economy for the trip and distance travelled. The other method that I mentioned earlier can be used for short-term calculations.

    You can probe the port up to about 4 or 5 times a second I think if you're just pulling down one particular value, but assuming that you want to get more than just that, even if you get a speed only once per second, just average out the speed difference between the previous and next second and you'll have a very accurate counter. Your speed changes are going to be linear on a second-by-second basis (i.e. within any given second you will most likely be only accellerating, decelerating or holding speed) so I'd estimate overall speed/distance measurements within 1 or 2 kph, but overall measurements will be almost dead on since you spend most of your time holding speed..

    In any case here's a collection of links that I have open in my browser windows, feel free to poke around and tell me if you find anything more! I am really interested in finding out about fuel economy and a few other counters that I don't seem to be able to get directly through mode 1.

    http://www.diy-efi.org/gmecm/
    GM ECM - other info links
    DIY 8192/160 baud interface with info
    A GM ALDL Information Page
    AKM Electronics - Manufacturers of some cables, connectors and adapters
    Raw diagnostics data dump info for one of the ECMs
    8192 baud async communications information page
    a bit of data dump + some info

    The J2190 SPEC!
    List of OBDII trouble codes
    another 8192 serial interface schematic
    yet another ALDL -> PC interface
    J1850 SPEC
    J2178 SPEC Page 1 page 2 page 4

    MIA is still J1979 spec which would be most helpful I think, since I can't find out any information about mode6/7 anywhere else... but rumour has it that mode6/7 is highly proprietary and varies manuf to manuf so that might not be of much help anyway.
    IN DEVELOPMENT -- '96 Mustang, lilliput with PII/450 laptop, custom DC-DC power supply, 60GB; Garmin GPS; 802.11g; compact keyboard, small graphical LCDs, OBDII.

  8. #18
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    Wow what cool information. Good job Telek! I did a project very similar to this last summer. I got as far as writing a VB app to extract OBD-II data and display it on my alphanumeric LCD. Looked almost identical to the pictures in the first post of this tread. I didnít figure out the MPG calculation though.

    I was thinking rather then rely on a PC for this, wouldnít using a microprocessor be better? Thatís my next project with my friend the BasicX.

  9. #19
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    Well what I want to do is actually replace parts of my instrument panel... so I have this 486 Datalux Databrick (supposedly dx4/100 but sysinfo reports sx/83) that measures like 2" x 5" x 12"... I won a 64MB flashcard on ebay for $6 that I was trying to figure out what to do with, so now I have a linux installation that can boot in about 12 seconds that is rock solid... Has FTP, HTTP, telnet servers, 4 com ports, parallel port, and takes 6MB of hard drive space and 4MB of ram to run... so I (will) have it set up on a 20MB r/o partition for the system and then 44MB of "data" where it can log just about everything it pulls out of the OBDII and GPS modules, then it'll pass that information along to my computer in the trunk via ethernet. This is small and only needs +5V so it'll be mounted up front... So I'll have a nice CAN (Car Area Network) setup :P

    So I figure that I can put at least my 128x64LCD in the instrument panel and have it display neat info directly relevant to driving, and then the 20x4 character display will be elsewhere and have more comprehensive info.

    What would be really cool would be to get an LCD that measures about 4" x 4" and just remove the spedometer and put a nice LCD in there... that would just kick ***.

    So I'll let everyone know how it works out once I get it all set up. I can't believe how many hours I've put into this thing to get seemingly nowhere, but if you want everything done properly I guess that it takes time!
    IN DEVELOPMENT -- '96 Mustang, lilliput with PII/450 laptop, custom DC-DC power supply, 60GB; Garmin GPS; 802.11g; compact keyboard, small graphical LCDs, OBDII.

  10. #20
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    telek, dude why you gotta think like me...

    i was planning on replacing the dash with a LCD screen, 7" wide screen, problem being they are a ***** to program a display for.. and id have to pick out a decent microcontroller (Im not quite that good at this **** yet, even though im in my senior year)

    goodluck, let me know if i can help..

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