FW: Processor selection for datalogger

[sdbartho at cca.rockwell.com]

>I would like to build a data logger to monitor a few engine
>parameters. 

No fair. That's my idea! ;)

>Does anyone have a feel for what the injector PW signal looks like
>(timing)?  I suspect it is a pulse between 1-10msec wide at idle.

I have some scms. from a friend's home-built datalogger, and he measures
from 1ms to 40ms. The application is a '87 Buick GN.(C3 ECM) It's an
interesting circuit, as he uses _no_  microprocessors.

>The technical service manual for my car describes the sequence and the
>crank angle at which the injection takes place, but it doesn't tell
>you how wide the pulses are.

Check out the section on injector balancing. It might give you a good feel
for the pulse width.

>How often do I need to sample to get a reasonable reading (i.e. is it
>5msec +/- 0.000001msec, needing a 1e6 counter, or is it 1-100msec,
>etc.)?  I realize this varies from car to car, but I am only looking
>for an ``order of magnitude'' starting point.

The GN datalogger uses 2 74HC590s. 

I'm looking at using a 68HC711G5, (if I can find one) and using the input
capture channels (6 possible on the G5) to measure this and all my other
PW signals. My concern is turning to sampling rate now, too, and I haven't
really dug into the systems issues. Let me know what you find out.

Dig
sdbartho at hwking.cca.rockwell.com
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