The ZX Spectrum laptop is a combination of two old computers: a ZX Spectrum 48k and a Toshiba Libretto 110.
The Spectrum is an iconic British computer from the 1980s, selling in
huge volumes (although I was brought up on a BBC Micro myself), and the
Libretto was one of the first truly tiny x86 laptops, quite amazing
when it appeared about a decade ago.

The modification keeps the case and keyboard of the Spectrum and the
main circuit board and display unit from the Libretto. Connecting the
keyboard was by far the most difficult part. I went through several
ideas to try and figure this one out.

The PS/2 port would be an obvious choice, but the Libretto only has
a PS/2 connector on the docking station attachment, which was too bulky
to fit into the Spectrum case. It’s the same story for the serial and
parallel port. The only standard communication options on the mainboard
are the PCMCIA slots and the IrDA port, and I wanted to keep the IrDA
port free for other communications. So the next idea was to try and
replace the Libretto’s keyboard more directly.






Luckily, the Libretto’s keyboard unit contained no active electronics
and was just a matrix of contacts on a plastic membrane. Logically then
it is possible to simulate the keyboard by shorting various lines at
the point they connect to the motherboard. However, the Libretto’s
keyboard connects to its main board by a 0.8mm pitch flexible circuit
connector, which is rather difficult to connect to. I tried several
attempts to connect flying leads to the membrane, using glue and silver
paint, which were mildly successful. The two keyboards are logically
just arrays of switches with row and column connectons coming out,
although the Libretto obviously has more switches, having an 8×13
matrix compared to the Spectrum’s 5×8. The challenge then was to pick
out the particular rows and columns to use on the Libretto so that each
key on the Spectrum made a valid keypress - some row/column
combinations might have been ‘blind’ for the Libretto, for all I knew.
I traced the keys to rows and columns on the Lib - mainly using digital
photos of the membrane and a flood fill tool.






Meanwhile, the physical construction provided some more challenges. I
had to cut away quite a lot of the case to fit in the display, and
getting the display straight and closing nicely was quite fiddly. The
case also had to be made a bit deeper to fit in the battery, so I made
up a frame to separate the top and bottom halves of the Spectrum case.

Having done that I could switch on the Libretto and make a few
keypresses on the Spectrum keyboard - nothing very sensible since
mapping a letter to the correct one would have been impossible. Before
I got very far, though, I realised the connections to the membrane were
unreliable and decided to solder directly to the Toshiba’s motherboard.
This is a very tricky task with the 0.8mm pitch, and I didn’t get all
the connectors but I did manage to get the 5 columns and 8 rows I
needed. The result isn’t very pretty, but did look a lot nicer than the
rat’s nest made by the membrane keyboard and glue mess. The Spectrum
keyboard remains connected by glue and paint, although it was easier to
make a robust connection to the wider membrane on its keyboard.

With those all attached reliably, I made up a new keymap for linux
so the keys would map correctly, and could actually type properly on
the Spectrum keyboard. Getting Debian onto the Libretto was the next
challenge. The PCMCIA-attached CD ROM drive that came with it had
packed up, and the floppy drive is a nonstandard type that won’t work
for Linux installations. There isn’t an ethernet port, even on the
dock, so the best option was to make up a bootstrap image on the Lib’s
hard disc, return it to the Libretto and boot it from there. This seems
to have worked fairly well.

The remaining problem, which I haven’t figured out yet, is how to
get some communications so I can download and install new software
without resorting to the dock (I have to take the mainboard out of the
case to fit it in the dock, so it’s not very desirable.) The PCMCIA
ports would seem the best option, but I haven’t been able to bring up
an ethernet card in it yet. The IrDA port is also a possiblity,
although downloading any data through that might require quite a lot of
patience.

So, what use is it? Well, the obvious application would be to load
up a ZX Spectrum emulator to have a portable retro games system. It’d
also be good for making notes while on the road - the batteries are
good for a couple of hours, which surprised me considering they’re ten
years old. Otherwise it’s just a bit of an objet d’art.

http://srimech.com/?page_id=18