Hey Steve -
Great information - thanks a bunch! By the way - very impressive
project with "Good Intentions".
I am lucky to work with a bright electrical engineer (I'm a Computer
Scientist myself) who was able to quickly explain the ZO75 schematic
to me. His explaination left me with a couple of questions that I
thought you might know answers to:
First, the obvious one, I can't quite make out the hand-written
notation in the bottom-left corner of Z075InterfaceSch.jpg - can you
let me know what it says?
Second, do you know what IC2 in the ZO75 "does?" That is, does it
simply change the serial input to another sort of signal the autohelm
interprets, or does it sends signals such as "steer left", "steer
right" by activating the appropriate pin on the connector?
I'm really hoping for the second scenario - because that would make
it easy for me to use my laptop to write a program to interpret the
NMEA messages, and output "steer left" "steer right" commands on my
parallel port, and amplify them to the appropriate level before
inputting them into the autopilot.

Thanks again for your help!
-Ben

"Steve" wrote in message ...
Ben, I have some general and some specific information and circuit diagrams
on these autohelm (pre-ST) equipment.. The compass and control circuitry is
basically the same on all of them.

I even have a circuit diagram (reverse engineered) for the ZO75 radio
interface that you mention. However it would be difficult to duplicate this
without the code for the 8749 processor chip.

You can find these on my web site at
http://hood.hctc.com/~esteve/private/manuals/

I have a Z075 interface if someone can read and duplicate the 8749 /w code.
From there, it would be fairly simple to build the rest of the circuit..
Failing in that, you can plagiarize the circuit and operating procedures in
your attempt to get the NMEA 183 to fuction with your AH800.. (the AH800
manual I have is for the type with the compass on top but the control
diagrams elsewhere should be of some help to you.

Good luck, I haven't been able to get NMEA to my AH3000 even with the Z075..
Let me know how you make out.

Steve
s/v Good Intentions