>
> Sometime back, someone on the list - sorry, my brain has gotten old and
> I can';t remember who - said they were working on reverse engineering
> that black box for the purpose of building a modern  black box that uses
> todays IC's for operation.

Ja, I was that jackass. I even got so far as to write some scratch code for
the PIC microcontroller  to do the job. But that's me, all sorts of good
ideas but no follow through.

From his comments, I understand that the
> original boxes were analog, and jumped through considerable hoops to
> derive the signals needed to operate. The replacement digital unit that
> would use the IC's would have no such problems, and not be so
> problematic.

Exactly. The old analog device manages to keep the engine at a certain
number of revolutions per minute, despite the inability to ACTUALLY COUNT
either revolutions or minutes. Doing it digitally is a simple matter of a
program that loops through the following instructions:

1. measure time between coil "sparks" to get idle speed
2. is idle too low? open ISV wider
3. is idle too high? close ISV a bit.
4. go to 1.

The throttle switch throws it into a "standby" condition, and the PS pump
switch merely modifies what it considers optimum RPM. Easy as a walk in the
park, really. I'm actually surprised they didn't just include this function
in the Digifant. It would have been so easy.

I think there was a plan to make plans available to build
> your own, as well as be able to buy one ready built. It is my sincere
> hope that who ever was doing this is carrying forth on the project and
> will give us an update.

The project stalled on the one thing I couldn't figure out: how, exactly,
does the idle control unit operate the idle stabilizer valve? Having but a
voltmeter, I can only tell that it receives voltage when the ignition is on.
Without some insight into how it's opening and closing the thing, I'm
stumped.

--
John Bange
'90 Vanagon - "Geldsauger"