Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!tut.cis.ohio-state.edu!ucbvax!pasteur!ames!killer!elg
From: elg@killer.Dallas.TX.US (Eric Green)
Newsgroups: comp.sys.amiga.tech
Subject: Re: Need advice on hardware projects
Message-ID: <7922@killer.Dallas.TX.US>
Date: 24 Apr 89 00:02:44 GMT
References: <10267@netnews.upenn.edu>
Organization: The Unix(R) Connection, Dallas, Texas
Lines: 62

in article <10267@netnews.upenn.edu>, ranjit@leguin.cis.upenn.edu (Ranjit Bhatnagar) says:
> I have no experience in designing bus arbitration circuitry,
> and the ancient white hardware manual doesn't say enough to 
> teach me.  But with someone else's electrical design (HINT!)
> I could probably manage the layout and mechanical stuff.
>>However, there may be some construction problems. I remember reading
> What about a board laid out in MacDraw or some similar CAD program,
> and then optically printed or silk screened?  I can do that in my

Sounds like you have most of the equipment needed to make PC boards,
then. Next thing you need is some resist, cleaner, and ferric
chloride, if you want to do quantity 1. Photographic floods probably
would supply enough UV for exposing the board.  Get the book
_Electronic Prototype Construction_ by Steve Kasten for more info
(your book dealer will probably have to order it direct from Howard
Sams Inc.). These are all very toxic chemicals, so follow his
instructions for handling and disposal.

> basement... except for drilling the holes.  How practical is it

Drilling the holes is no big problem. Any ordinary drill-press will
do. Kasten gives a way of getting around the registration problems
that can occur, too.... etch one side, drill, then line up the other
side's holes & shoot & etch the other side.

> I got nice answers about low volume and high startup costs, but
> what I really was hoping for was design hints.  Is refresh circuitry
> qualitatively different for such an application? 

Maybe someone on the net could help by digging up chip #s/manufactures
for refresh controllers. I just wish to point out that doing a memory
board that connects to a 25mhz 68020/68030 is very different from
doing a memory board that slaps on the side of an Amiga 1000....
> How about a system that sits above the 1000 or below the 500, just
> by rotating it?  I like the subsystem idea because it saves desk

Won't work. You'd have to do some fancy sheet-metal work, and if you
are off by a micrometer, you have an unsightly gap, mechanical stress
on your edge connector, or some other nastiness. Whereas, if you slap
it on the side, any old box will do (as long as it's big enough for
the cards!). Looking at the ET slap-on-the-side, it looks suspiciously
like an ordinary external floppy-disk case.

Not to mention that my keyboard is already high off the floor, without
adding another 4 inches ;-).

> Any objections to having the power supply in
> a separate box?  That way it can be stowed on the floor to save
> desk space, or on the desk to save floor space.  As Eric
> pointed out, any old surplus power supply will do... there's

You're getting aweful fancy for a hacker's project. The question of
"where do I put it?" for the power supply depends on exactly what kind
of power supply and what case you get. In my case, I'd probably put a
spare PC-clone power supply outside of the enclosure (it is in its own
box already), and run the power to both the card cage and to the Amiga
500 (which has an amazingly wimpy power supply).

--
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