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Auto Hobbyist DAQ setup?

Discussion in 'Electronic Basics' started by David Geesaman, Dec 7, 2005.

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  1. I'm thinking about making a laptop-based DAQ system for monitoring the
    behavior of some systems on my car. The point is to monitor and log a few
    values at once while keeping my eye on the road. I suspect the ECUs on this
    car get flaky, and I'd love to trace down the source of the problem. I
    think I'll lose interest if this project costs me more than $200 total.

    This requires:
    - sensing absolute pressure from 0 to 3 Bar.
    - 3-5% accuracy would be fine. I won't need to log many hours with this
    thing running, either.
    - sensing voltages (DC and duty-cycle signals) from the ECU pinouts, 0-15v,
    with a max rate of about 1kHz. (Hence, 2-5kS/s sampling, which isn't asking
    much these days). Duty cycle output frequencies are on the order of 1kHz.
    - total of 2-3 pressure sensors and 2-3 voltage sensors, with a minimum of 3
    at once. Of course more would be better.
    - interface to the cheap laptop, preferably with no programming and
    additional software needed. I see many USB devices, and though the laptop
    is really old (Pentium 200MHz), I can get a PCMCIA USB card for $12.

    I found a nice DAQ unit
    http://www.hytekautomation.com/Products/IUSBDAQ.html which leaves $100 for
    buying sensors.

    1) The DAQ units I see are 0-4V and -10 to 10V. I will be reading a range
    of 0-15v. What's the best way to handle this?
    2) What kind of sensors should I get, and how will I power them? (of
    course, I have 12v available). I could probably buy some old MAP sensors
    from the junkyard, or is there are cleaner way?
    3) Any other tips? I'm a mechanical engineer, so the cheapest/easiest way
    to logging my values is what I value most.

    Thanks for any advice,

    Dave
     
  2. Jan Wagner

    Jan Wagner Guest

    If your car has an OBD / OBD-II interface, probably located
    somewhere in the fuse and relay box, then you can read out some of
    that data with a simple serial port wire and software on your laptop
    or PDA.

    http://www.planetfall.com/~jeff/obdii/
    http://www.scantool.net/products/index.htm
    http://www.autotap.com/

    Stocking the car up with your own DAQ center module and multiple
    sensors will probably get more expensive than using the onboard
    computer directly with some DIY cable...

    - Jan
     
  3. Thanks Jan. The car in question is a 1994 Mazda RX-7. So it's OBD-I,
    and does not appear to have a standard connector. The aftermarket ECUs have
    a controller that shows this detail, but no such product exists for the
    stock ECU.
    I just found another RX-7 owner who is building one using an even
    cheaper USB-based DAQ. He is using op-amps to isolate the voltage readings,
    and a circuit to convert the duty-cycle signal to a single voltage, rather
    than supersample to form the duty-cycle waveform (and do further
    gymnastics).

    Dave
     
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