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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 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,

  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.

    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

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