GM ALDL interface Schematic

[Frederic Breitwieser]

Mr. Joe said:
>Don't forget about the rest of us!

I successfully copied his basic program from his website to my notebook,
and after a little timing adjustment, managed to get ALDL information by
the pound from the ECM on my garage floor.  Of course, the ECM isn't
connected to the engine, just the wiring harness as slopped in a large
moving box.

Anyway, I created a simple 1-transister interface that connects the ALDL
connector to the parallel port successfully.  Sean's code needs one
additional line of code to turn one of the printer control lines (Auto
Linefeed) to a "high" so the circuit has +5V power.  I cheated and tapped
power off the external mouse connector by shoving a wire into the jack <G>.
 That works fine too, but looks worse than his code <grin>.

The transistor ciruit does nothing but convert the 12V signal from the ALDL
connector to a 5V signal from the tapped +5V source, basically representing
a cheesy buffer.  One could use an RS232 buffer chip, but why bother.

Sean, Joe, I sent the JPG to you guys directly, if you want to include it
on your website, you are more than welcome :)  If anyone wants to convert
the program to C to run under win3.1, win95, or WinNT and automatically
adjust timing to the PC, I'd love to be involved :)

Thanks!
Frederic Breitwieser
Homebrew Automotive Mailing List
Bridgeport, CT 06606
http://www.geocities.com/MotorCity/Downs/4605/index.html
(Portable Webserver Link Address)

1989 AG Hummer 4-Door
1993 Supercharged Lincoln Continental
2000 Mid-Engine Sports Car <smile>

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