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Auto Hobbyist DAQ setup?

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David Geesaman

Jan 1, 1970
0
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
 
J

Jan Wagner

Jan 1, 1970
0
David said:
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.
...
I found a nice DAQ unit
http://www.hytekautomation.com/Products/IUSBDAQ.html which leaves $100 for
buying sensors.

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
 
D

David Geesaman

Jan 1, 1970
0
Jan Wagner said:
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

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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