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Thread: Old car/engine, non ODB, how to get RPM/speed/temp/etc into carputer

  1. #1
    Raw Wave Confused's Avatar
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    Question Old car/engine, non ODB, how to get RPM/speed/temp/etc into carputer

    OK guys, I'd like to get some good information, and possibly some hardware/software solutions to this problem

    Now, things that will be needed are:
    Speed
    RPM
    Temp (coolant, oil, whatever)
    Fuel level
    Voltages
    Oil pressure
    and others (any suggestions)

    Now, on most older cars, with analogue dashes, many of these are controlled by a voltage/signal going into the back of the instruments. The only "mechanical" one of these would be the speed, which will come in via (normally) a cable attached to the gearbox, which spins to give a readout on the speedo.

    For a totally digital dash, these values would need to be read by the PC, and output to the screen. I am willing to try to write custom software to do this (probably in VB, as it's the only real thing I know), but I need some help with the hardware part.

    What would be useful is some kind of hardware to get all these (probably voltage) signals into the PC in a format that can be read. The ones that will need most attention, and the quickest update, will be speed/rpm.

    This is a throwout to everyone to help!



    Garry
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  2. #2
    FLA gospeed.racer's Avatar
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    Well, back in high school a few of the electronics students built Digital Dakota kits for their final project. Might have a look on their site here:
    http://www.dakotadigital.com/
    I know the speedo/tach combo was popular, and was not a very expensive kit. Here is the interface to go from a rotating speed cable to a signal: http://www.dakotadigital.com/Detail....umber=SEN-01-2. These are kits that are used to provide a digital dashboard, so maybe they are a step in the right direction for you.
    2005 Ford Focus ST

  3. #3
    Constant Bitrate RX7FDTT's Avatar
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    Quote Originally Posted by gospeed.racer
    Well, back in high school a few of the electronics students built Digital Dakota kits for their final project. Might have a look on their site here:
    http://www.dakotadigital.com/
    I know the speedo/tach combo was popular, and was not a very expensive kit. Here is the interface to go from a rotating speed cable to a signal: http://www.dakotadigital.com/Detail....umber=SEN-01-2. These are kits that are used to provide a digital dashboard, so maybe they are a step in the right direction for you.
    Check these out ...

  4. #4
    Raw Wave Confused's Avatar
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    Thanks for that link, gospead.racer Looks like it might be a "failsafe" option if all else fails

    Anyways, from a little googling, I was able to find this. On that page, is linked to the mini-datalogger pic below:



    If my guesses are correct, then the tach, petrol level and temps are just voltages passed to the stock guages (they're just 2 wires into the back of each, i'm guessing a signal, and a common ground). Of course, this is all basing it on the fact that all the guages work on variable voltage depending on their status.

    With 8 inputs via this, and the VVIO.dll code for C and VB, as well as DOS and Linux, it's looking quite interesting.

    Then the only other thing will be some way to get a linear voltage from the speedo cable coming from the gearbox. Possibly a high sensivity dynamo? Any ideas on this one?

    Some good info coming in now


    Garry
    Co-Developer of A.I.M.E.E
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  5. #5
    Low Bitrate
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    Confused,

    I am also interested in this. I would be very curious to see how you solve this. Please keep us all up to date as too how you proceed with this. I have an old Alfa Romeo and would like to get these features on screen.

    Thanks,
    Simon

  6. #6
    Low Bitrate killerfishes's Avatar
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    tach will be a pulse out from a/the coil, gas is usually a resistance,speed is also probably a pulse and other may be voltage or resistance.
    now working on my Dodge Dak
    toshiba portege == done
    audigy2 NX == done
    7" flush mount == 0%
    pimp rating == 48%

  7. #7
    mst
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    The tack will be a pulse ,so "just" use a freq/volt converter;the speed is for many cars e magnet turning round and "dragging" the speed needle with it,so a hall contact and a freq/volt should do.
    I am planning to use the hall contact with a PIC to drive a stepper motor to move the speed needle to get a precise speed

  8. #8
    Raw Wave Confused's Avatar
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    Right, i've got some more information (from my dad) which should help a little This is just me putting my thoughts down so they might not be in any good order, or make too much sense...apologies for that

    Right, firstly, fuel level/temperature(s). Most older cars have a regulator, which goes through the needle, to the reciever, which goes to ground. The reciever works on changing resistance. Therefore, all you need to do is keep the current stuff, and measure the voltage change in the needle due to the differing resistances from the reciever.

    For tach, it does indeed work on a pulse from the engine. For my car at least, this pulse is put through a small chip/circuit in the tach housing itself, which converts this pulse into a voltage, which is attached to a small motor which turns the needle to where it needs to go. As this last bit is working on voltages, you can keep the circuit board, and remove the motor/needle part of it, and measure this. I am not sure as of yet whether this will be linear or not...but the software part of it should be able to cope with that (well, i'm hoping anyway )

    For speed, that is a cable which, as mst said, "drags" the needle round. This is the bit that I'm not too sure about...mst, maybe you could help/provide more information on how a differing voltage can be read from this??

    However, before I can really start on this, I need to get my engine rebuilt and up and running, preferably in the car That will take me a couple of months I guess, given the weather (well, the lack of good stuff) and temperature (or, again, lack of)


    Garry
    Co-Developer of A.I.M.E.E
    www.aimee.cc

  9. #9
    mst
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    Well,sorry but my knowledge is only theoretic,for the time being,from "the microcontroller application cookbook"by Matt Gilliland:there are two types of Hall-effect sensors:linear and digital.In the linear the output voltage is proportional with the revolution;the digital measures the revolutions direct.I will try to scan the pages from the book and PM then to you,he explains it better then me(there are even some schematics)

  10. #10
    Raw Wave Confused's Avatar
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    Cheers for that, mst

    I haven't even heard of Hall-effect sensors...so anything I learn about those is a bonus


    Garry
    Co-Developer of A.I.M.E.E
    www.aimee.cc

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