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

  1. #51
    Join Date
    May 2001
    bobjimwilly, I'm done with computer side of the system, but still need to interface sensors (temp, speed, fuel gauge, etc.). I'm using a PIC chip to interface to the sensors and send the data via serial port. Shouldn't be tool hard to do. I sold my 67 Mustang and stop working on it (didn't have time also).
    66 Mustang

  2. #52
    Join Date
    Mar 2006

    Lightbulb gtech pro

    why don't you use Gtech pro?

    <From the site>

    There is a lot of new products that plug into your OBDII (On Board Diagnostics) port and claim to measure horsepower, torque, 1/4 mile etc. We have studied the OBDII protocol and the problem is that OBDII system was designed as a diagnostic tool to be used in a mechanics shop. So things such as timing accuracy and speed of the sensor readings were not critical. But for performance measurements you need exactly those things. So when it comes to measuring performance through OBDII that is a problem. It can be done easily but it's not accurate.

    For performance measurements you need acceleration. OBDII devices calculate the acceleration from speed and time. In theory there is nothing wrong with that method but the problem is resolution (how often is the speed updated?) With OBDII it's only a few times per second! So acceleration readings are "choppy" and not accurate

    The best way to get accurate acceleration is to measure it with an accelerometer. GTECH takes 4000 readings per second from each of its x,y and z precision accelerometers!

    </From the site>

    []s, Rodrigo Ratan

    Quote Originally Posted by Confused
    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:
    Temp (coolant, oil, whatever)
    Fuel level
    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!


  3. #53
    Neither darque nor pervert DarquePervert's Avatar
    Join Date
    Apr 2004
    Quote Originally Posted by rodrigoratan
    why don't you use Gtech pro?
    First of all, you're resurrecting a two year old thread.
    Second, the GTech Pro has no means of interfacing with a PC In realtime, which is what can be done with OBD.
    Lastly, the GTech isn't going to provide some of the data that is wanted like engine temps, fuel levels, voltage readings, etc.
    Have you looked in the FAQ yet?
    How about the Wiki?

    Under normal circumstances, a signature would go here.

  4. #54
    Join Date
    May 2006
    ok so i'm going to help ressurect this 2 yr old thread. but whats the current situation of this or other projects simmilar. ive searched and everyone is obd2 this and obd2 that, kind of sucks for us old school. any projects like this?

  5. #55
    Variable Bitrate
    Join Date
    Feb 2005
    West Valley City, Utah
    I will be looking heavily into adopting it to work on my cougar, it should be the same for any mustang 87-95, so I will prolly hit up a mustang board and see if I can find anything.
    Progress,.... that is what I keep forgetting ;)
    planning_[++++++++++]. 110%
    parts___[++++++----] around 60%
    install___[-----------] -9,000%

  6. #56
    Maximum Bitrate SAScooby's Avatar
    Join Date
    Feb 2004
    Johannesburg, South Africa
    find the project that has the porsche 944 in it, with linux, theres loads of detail on how to obtain this information from the car itself
    Nano ITX / 512 MB / 60 GB / Panasonic slot load / M1-ATX / Bu303 / Sound blaster 24 / PPi amps / rockford sub

  7. #57
    Low Bitrate
    Join Date
    May 2005
    I just realized how old this thread is, but i have written out a lengthy post so i will post it. Maybie someone will find it helpful

    Quote Originally Posted by Confused
    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?
    One solution would be be to just use a motor with a resistor capacitor filter on it's output. In theory the voltage produced by running a motor backwards is proportional to the speed of shaft rotation. I don't know how much the tach shaft is geared down, but for best results you would want its output at it's top RPM to be somewhere near the rpm the motor spins freely at it's rated voltage. This may take some gearing. Also, you need to make sure the output voltage output from the motor never goes above the max your ADC can take. You can use a clamping diode rated for the right voltage in parallel with the motor to make sure this does not happen in some extreme event. The output from the motor by itself is slightly choppy due to the way the motor works, so you need some sort of filtering. A simple resistor-capacitor filter would work.

    A bette but more complicated solution would be to use a HAL effect sensor or encoder with a pic or other logic to interface iwht it

    Beware anything that uses an accelerometer to figure out speed! IT WILL NOT BE ACCURATE WITH TIME unless you are dealing with stuff from aircraft or cruise missiles, or its costs ALOT. I have designed intertial guidance systems.

  8. #58
    Join Date
    Jul 2006
    This is an old thread but this info could come in handy for anyone who has an older car.

    The easiest solution for obtaining vehicle speed from any car that has a mechanical speedometer is to use one of GMs older style VSS sensors. These screw onto the speedometer cable and use an IR LED sensor/receiver to generate "x" pulses for every revolution of the cable. Most of these units generate 2002 perfect digital pulses per mile travelled (based on being installed in a GM transmission).

    If you disassemble one of these units, you'll find a wheel with a series of holes in it that rotates in unison with the cable. Count the holes to see how many pulses you'll get per revolution of the cable. Then determine the rate of rotation per mile of your speedometer cable per your vehicle. Anyone with specs on speedometer driven gear ratios should be able to help you figure this part out.

    EDIT: Yes, Dakota Digital makes a "generic" VSS which might be easier to adapt to any vehicle. If you have an older GM car, however, using the GM VSS is very easy. This came out on 1981 models with Computer Command Control and was used for many year after that until the VSS was eventually integrated into a more complex system.

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