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January, 2012

  1. Speedo is working after all

    January 29, 2012 by frank

    Decided to take another look at the speedo today.  Turns out I forgot to solder the wire for the VSS signal.  After soldering in that last wire, the speedo works.  It indicates 3 km/h, not much, but at least I now know the speedo is working.

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  2. Accidently deleted all pictures :(

    January 23, 2012 by frank

    Did an update of a WordPress plugin yesterday and I didn’t think it was necessary to take a backup of the database.  I was wrong.  The update deleted all columns in the database, so all links to the pictures are gone.  I spent about 5 hours yesterday and today putting back the correct links.  I had to look up all my pages and posts in google cache, figure out which pictures I had used, find them back in about 55 albums and correct the links.  Not fun.  I think I have another 2 or 3 hours work left to get everything back in order.

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  3. VR circuits

    January 17, 2012 by frank

    Here’s a couple of VR circuits that I can use to convert the ~AC signal from the transmission to a 5V square wave the the S2000 cluster accepts.

    Decided to oder a LM1815 and build this VR circuit.

     

     

    Very simple VR circuit.
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    Very simple VR circuit.

    Just after ordering I found this circuit.  Needs only a couple of resistors and 2 transistors, so this is a good option as well.  Probably gonna stick with the LM1815 based circuit though, now that I’ve ordered the chip …

     

     

    Here’s another one with extremely low parts count.  I actually have such a Maxim chip, but it’s surface mount so very difficult to solder :(

     

     

    Code for the pic is here.

     

     

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  4. speed conversion

    January 15, 2012 by frank

    41.5Hz @ 50km/u = ±4800ppm
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    41.5Hz @ 50km/u = ±4800ppm

    Put the Westfield with its wheels in the air to test the speedo.  Nothing :( .
    Don’t know exactly why it isn’t working, my oscilloscope gets a reading so it should indicate something.

    At 50 km/h (13.889 m/s) I have 41.5 Hz, iow 41.5 pulses for 13.889 m or 4800 pulses per mile.  This is weird as it’s supposed to be 4000 ppm.  Either way, it should read something, even at 4800 ppm.
    The speedo expects 156000 ppm.  I drove the car up to 170 km/h, so the speedo should at least indicate 5 km/h, but I get nothing.
    Difficult to diagnose if it’s the speedo or a problem with my signal.  Will have to do some more testing.

    Since the signal is 4800ppm, I can use Jean Bélanger’s PWM converter circuit to multiply the square wave signal by 32 (actually 32.5, but 32 is close enough).  However, if it turns out to be 4000ppm, my speedo will be reading 20% slow  with the 32 multiplier …

     

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  5. Oil pressure in Tunerstudio

    January 7, 2012 by frank

    I have a 90-94 ‘real’ oil pressure sender but no real oil pressure gauge in my S2000 cluster, so I’m using the MS3X to trigger my oil warning light at a preset value.

    The wire coming from the sensor no longer goes to the instrument cluster but to the MS3X on port ADC13 instead.  Since the oil pressure sender outputs no voltage (it’s a simple lineair resistor), a bias resistor is added on the MS3X card in the R67 position.  The oil pressure sender has a fairly low resistance so I used 330ohm to get good accuracy.  Worst case, this pulls about 15mA through the sensor so it shouldn’t be a problem.

    The factory manual mentions these resistor values:
    0psi => 52 ohms
    90psi => 16 ohms

    With a 330 ohm bias resistor we can calculate the corresponding input voltage on ADC13:
    0psi => 5*52/(52+330) = 0.68V
    90psi => 5*16/(16+330) = 0.23V

    With this we can calculate the 0V and 5V values in Tunerstudio:
    0V => (90-0)/(0.23-0.68)*(0-0.68) =  136
    5V => (90-0)/(0.23-0.68)*(5-0.68) = -864

    Enter these values in Generic Sensor Input 1
    sensor – source: Spare ADC (ADC13)
    Transformation: Linear mode

    Now you can use a spare output port to trigger the oil warning light when oil pressure goes below 15psi.  I use these values:
    Output port IAC2
    Power on value: 1
    Trigger value: 0
    Output channel: sensor01 < 15  Hysteresis 2

    If you have a real oil pressure gauge, you probably want keep using it (no point in disconnecting a perfectly good oil pressure gauge!).  You’d obviously need no bias resistor and you need to make sure you do NOT send over 5V into the ADC port.  The gauge works with 12V, so it’s probable that you measure more then 5V over the oil pressure sender (I never checked though).  If so, you’ll have to use a voltage divider to bring it down to 5V.
    Obviously, you’ll have to do some math since you’re now using an unknown bias resistor (easy to calculate its value).

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