AN EXPANSION SLOT BOX FOR AMSTRAD PPC PORTABLE COMPUTER

                       Steve Asher

When I bought the PPC, I quickly found that I was limited
in what I could add to the machine. Colour monitor, Mouse, and
Ram Drive proved useful, but I still liked the idea of adding
External Hard and Floppy Drives, Joystick etc.

I saw ads in English magazines for Internal Hard Drives
and External Expansion Boxes, but they were all pricey and
not readily available in Australia. With a little pressure
from Tony, I started to work towards making my own Slot Box.

The first breakthrough was the Technical Reference
Manual from Mr Computer. I studied the Expansion Socket
Pinouts, and slowly designed my board. "Interfacing To The
IBM Personal Computer", published by Sams, proved invaluable
for information on "conditioning" the various signal and
power leads.

A number of people helped me, by answering my questions
and giving support..e.g. [Tony S and David S].
I built it on a Tandy solder pad board [not veroboard]
approx 6.25" x 4.5", using 3 IBM Sockets, to allow me to use
a Hard Disc Controller, Joystick Controller, and perhaps a
suitable Floppy Controller.

I set out all components, and when happy with layout,
I "tacked" the IC, IBM, and Expansion Sockets with several
solder spots to the Tandy board pads. As PPC uses 25 and 37
way "D" connectors, and I was using 26 and 40 way "IDC"
sockets, I marked ECA socket as 1 to 13, and 14 to 25, and
did not use tag 26. For ECB, I numbered row 1 from 1 to 19,
leaving 20th tag spare, and numbered row 2 from 20 to 37,
leaving the 19th and 20th tags spare. [Note: If you build
yours this way, make sure you understand this numbering:
the vacant tags are normally numbered 20, 39, and 40.].

I ran the wires for Power in parallel across the
Board, and up the side of each IBM Socket to the appropriate
tags..i.e. like a tree with branches, and to the various
IC tags and Resistors/Capacitors as described in Wiring Run.
For the Signal Wires, I ran them starting either from
IBM Sockets or Expansion Sockets depending on which was
easiest for me at the time...usually from Left to Right.

The 8 Data Lines are each connected to the tags of the 47pF
Capacitor, and 10K Ohm Resistor, and then to tags of IBM Skts.
The Buffered Signals are run from Expansion Skt to incoming
tag of 74HC244 IC, and from outgoing tag to IBM Skts.
Be careful with the Numbering of the IC's, as there are 8
Buffers in each, packed in like sardines. I.e. first cct.
uses tag 2 for incoming signal from PPC, tag 18 for outgoing
signal to IBM Skt., while 2nd cct. uses tag 17 for incoming
signal from PPC, and tag 3 for outgoing signal to IBM Skt.
I am emphasising this because I made several mistakes myself!

The signal wires which require no conditioning are simply
run from the PPC Expansion Socket to the appropriate IBM Skt tag.
I have used 3 IBM Sockets, and commoned all the signal wires by
looping  across from socket to socket. As the IBM Skts are at 1"
centres, I cut the looping wires approx 1.5" long, and stripped
approx 1/8" from each end for soldering.

The Connecting Cables from PPC to Expansion Box are kept as
short as possible to minimise noise and signal distortion..e.g.
about 6". They use 25 and 37 way IDS "D" Connectors at PPC end,
and 26 and 40 way IDS Connectors at Expansion box end. To reduce
noise, I wrapped the ribbon cables with Alfoil for shielding, and
protected the Alfoil with packing tape. [Fairly rough!].

                 PARTS LIST

1x Tandy/Radio Shack Circuit Board # 276-147
3x 62 way IBM Sockets              2x 20 way IC Sockets
2x 74HC244 "Non Inverting Buffer" IC's
8x 10,000 Ohm 1/4 Watt Resistors   8x 220 Ohm 1/4 W Resistors
2x 4,700 Ohm 1/4 Watt Resistors    2x 22uF Capacitors
8x 47pF [picofarad] Capacitors
1x 25 Way Male IDC "D" Plug   1x 37 Way Male IDC "D" Plug
1x 26 Way IDC Header          1x 40 Way IDC Header
1x 26 Way IDC Line Socket     1x 40 Way IDC Line Socket
1x 5 Way PCB Mount Screw Terminal for Power Connection
Sufficient Ribbon Cable for the two connecting cables
Box to suit project and your application e.g. Jaycar HB 5468
Power Supply  [+5V, +12V] to suit your application
Wire, screws, nuts, bolts, holes etc.
Approximate Cost is $120 excluding Power Supply

           SUGGESTED IMPROVEMENTS:

As I did not know whether or not it would work when I started
building, I tried to keep construction simple and costs low.
There is some interest in designing a Printed Wiring Board,
which will speed up construction time, and improve immunity
to noise and signal distortion.

Also, use of Shielded Cable with "D" Connectors at each end
would improve noise immunity. However, the "D" Sockets I
have seen will not match the holes in the Tandy board! The
information in this article is freely given, and you are
free to use it as you wish, but I cannot guarantee that your
application will be successful.

This design could possibly be modified to suit other machines
such as Toshiba, but the buffering and proprietary expansion
would need to be studied carefully and altered to suit.

Tony and I are both using 20 Meg Hard Drives with our
PPC's, and they work well with this versatile machine.