ZX81 40th Anniversary

So the Z80-powered doorstop that got so many people started with computers was launched 40 years ago.

My story is that we never had one: we had three, but only for a week each. It’s not that they failed, either. My dad, who ran the computer bureau at King George V Docks for the Clyde Port Authority, was Glasgow’s representative on the European Association for Data Processing in Ports (EVHA). The group was looking at ways for automating ship identification, efficient berthing and documentation handling.

All the ports had data centres, but most of the mainframe time was for predefined tasks such as dock-worker payroll. There wasn’t the budget for computer time to try some of the experimental projects that may have helped with port automation.

Several EVHA members were trying home computers unofficially, but many of them were too expensive to come in under expense account rules. These “big” micros required a business case and purchase order to buy. The ZX81, limited as it was, did fit in the expense budget and – equally importantly – fitted into my dad’s suitcase as he made his monthly trips to Europe.

The week before my dad was scheduled to leave, he’d buy a ZX81. Of course, it needed “testing”, something me and my brother were only too happy to do. At the end of the week, it would get packed up and on its way to Europe.

I’m not sure if the clandestine micros were ever actually used for controlling ship traffic (you get considerably fewer than three lives manoeuvring an LNG tanker), but more likely in simulation. I understand that the ZX81 was able to simulate the traffic management for the entire Port of Rotterdam for a while, at least until its RAM pack wobbled.


reposted from ZX81 40th Anniversary – Histories – Retro Computing

Book: Fortran techniques with special reference to non-numerical applications (1972)

Programming flow diagram, with the flow of a program using subroutines on the left ("closed coding") and the same structure on the right written as a series of GOTO-controlled sections ("open coding") to save computer memory and execution time
Subroutines do, however, bring with them considerable
overheads in both space and execution time
.”

Imagine you have a programming task that involves parsing and analyzing text. Nothing complicated: maybe just breaking it into tokens. Now imagine the only programming language you had available:

  • has no text handling functions at all: you can pack characters into numeric types, but how they are packed and how many you get per type are system dependent;
  • allows integers in variables starting with the letters I→N, with A→H and O→Z floating point;
  • has IF … THEN but no ELSE, with the preferred form being
    IF (expr) neg, zero, pos
    where expr is the expression to evaluate, and neg, zero and pos are statement labels to jump to if the evaluation is negative, zero or positive, respectively;
  • has only enough memory for (linear, non-associative) arrays of a couple of thousand entries;
  • disallows recursion completely;
  • charges for computing time such that a solo researcher’s work might cost many times their salary in a few weeks.

Sounds impossible, right? But that’s the world described in Colin Day’s book from 1972, Fortran techniques with special reference to non-numerical applications.

The programming language used is USA Standard FORTRAN X3.9 1966, commonly known as Fortran IV after IBM’s naming convention. For all it looks crude today, Fortran was an efficient, sod-the-theory-just-get-the-job-done language that allowed numerical problems to be described as a text program and solved with previously impossible speed. Every computer shipped with some form of Fortran compiler at the time. Day wasn’t alone working within Fortran IV’s text limitations in the early 1970s: the first Unix tools at Bell Labs were written in Fortran IV — that was before they built themselves their own toolchain and invented the segmentation fault.

The book is a small (~ 90 page) delight, and is a window into system limitations we might almost find unimaginable. Wanna create a lookup table of a thousand entries? Today it’s a fraction of a thought and microseconds of program time. But nearly fifty years ago, Colin Day described methods of manually creating two small index and target arrays and rolling your own hash functions to store and retrieve stuff. Text? Hollerith constants, mate; that’s yer lot — 6HOH HAI might fit in one computer word if you were running on big iron. Sorting and searching (especially without recursion) are revealed to be the immensely complex subjects they are, all hidden behind today’s one-liner methods. Day shows methods to simulate recursion with arrays standing in for pointer stacks of GO TO targets (:coding_horror_face:). And if it’s graphics you want, that’s what the line printer’s for:

Damped cosine 2d function density plot rendered as mono-spaced characters, approximately 60 colums across, made up of only X, 0, *, +, - and space characters
… the most serious drawback to a density plot of the type shown above is the limited number of characters used to represent the height above the page.”
(This image was deemed impressive enough by Cambridge University Press that they used it as the cover of the book. The same function became a bit of a visual cliché, with home computers being able to render it in colour and isometric 3D less than a decade later.)

Why do I like this book enough to track down a used copy, import it, scan it, correct it and upload it to the Internet Archive? To me, it shows the layers we now take for granted, and the privilege we have with these hard problems of half a century ago being trivially soluble on a $10 computer the size of a stick of gum. When we run today’s massive AI models with little interest in the underlying assumptions but a sharp focus on getting the results we want, we do a disservice to the years of R&D that got us here.

The ‘charges for computing time’ comment above is from Colin’s website. Early central computing facilities had the SaaS billing down solid, partly because many mainframes were rented from the vendor and system usage was accounted for in minute detail. Apparently the system Colin used (when a new lecturer) was at another college, and it was the custom to send periodic invoices for CPU time and storage used back to the user’s department. Nowhere on these invoices did it say that these accounts were for information only and were not payable. Not the best way to greet your users.

(Incidentally, if you hate yourself and everyone else around you, you can get a feel of system billing on any Linux system by enabling user quotas. You’ll very likely stop doing this almost immediately as the restrictions and reporting burden seem utterly alien to us today.)

While the book is still very much in copyright, the copy I have sat unread at Lakehead University Library since June 1995; the due date slip’s still pasted in the back. It’s been out of print at Cambridge University Press since May 1987, even if they do have a plaintive/passive aggressive “hey we could totally make an ebook of this if you really want it” link on their site. I — and the lovely folks hosting it at the Internet Archive — have saved them from what’s evidently too much trouble. I won’t even raise an eyebrow if they pull a Nintendo and start selling this scan.


Colossal thanks to Internet Archive for making the book uploading process much easier than I thought it was. They’ve completely revamped the processing behind it, and the fully open-source engine gives great results. As ever, if you assumed you knew how to do it, think again and read the How to upload scanned images to make a book guide. Uploading a zip file of images is much easier than mucking about with weird command-line TIFF and PDF tools. The resulting PDF is about half the size of the optimized scans I uploaded, and it’s nicely tagged with metadata and contains (mostly) searchable text. It took more than an hour to process on the archive’s spectacularly powerful servers, though, so I hate to think what Colin Day’s bill would have been in 1972 for that many CPU cycles … or if even a computer of that time, given enough storage, could complete the project by now.

“space acid poisoning …”

Thanks to users sbadger and lurkio on the stardot forum, I’ve been reunited the original BBC BASIC one-liner that begat 2d Star Dodge/Stardodger: Asterisk Tracker!

Asterisk Tracker

It was published in the December 1984 edition of BEEBUG Magazine (vol. 3, issue 7; page 9) and is credited to N. Silver.

It’s impossibly short:

1L=0:REP.L=L+3:MO.4:DR.1279,0:DR.1279,452:MOVE1279,572:DR.1279,1023:DR.0,1023:F.I=1TOL:V.31,RND(32)+5,RND(31),42,30:N.:P.(L-3)/3:X=0:Y=512:REP.PL.69,X,Y:X=X+4:Y=Y-(INKEY-74+.5)*8:U.PO.X,Y)=1ORX=1280:U.X<1280:V.7:REP.U.INKEY-99:RUN

It makes extensive use of BBC BASIC’s abbreviations, and the writeup even warns

… Here the programs are extensively abbreviated so that the line will fit into Basic’s keyboard buffer. Because of this, you cannot edit a LISTed version, and so, to allow for errors, it is best to spool out a copy of the text to tape/disc initially. This can be achieved as follows:

*SPOOL PROGRAM
type in program
*SPOOL

The program unwinds to something much more understandable:


   10 L=0
   20 REPEAT
   25   L=L+3
   30   MODE 4
   40   DRAW 1279,0
   50   DRAW 1279,452
   60   MOVE 1279,572
   70   DRAW 1279,1023
   80   DRAW 0,1023
   90   FOR I=1 TO L
  100     VDU 31,RND(32)+5,RND(31),42,30
  110   NEXT
  120   PRINT (L-3)/3
  130   X=0
  140   Y=512
  150   REPEAT
  155     PLOT 69,X,Y
  160     X=X+4
  170     Y=Y-(INKEY(-74)+.5)*8
  180   UNTIL POINT(X,Y)=1 OR X=1280
  190 UNTIL X<1280
  200 VDU 7
  210 REPEAT UNTIL INKEY(-99)
  220 RUN

The instructions are typical of the day:

The first game (called ‘Asterisk Tracker’) is a very simple game in which you have to guide a ‘snake’ across the screen, whilst avoiding the stars. As the game progresses, more and more stars will be displayed, and the ease of the game rapidly disappears. The Return key guides the ‘snake’ upwards, but it moves down if Return is not pressed. Aim your ‘snake’ for the gap in the wall, and don’t touch any objects as this causes instant death from space acid poisoning!

Um, yeah, N. Silver, whatevs …

It’s pretty amazing that three type-ins could fit on a page: especially when you consider that the BEEBUG magazine was A5!

beebug vol 3 issue 7 page 9

If you want to play it (and who wouldn’t? We wasted days on this game) you can either run this Asterisk Tracker alone in the browser: Asterisk Tracker, or lurkio has combined them into one, and put them here: Beebug One-Line Games (Asterisk Tracker, a Truffle Hunt clone, and a treasure hunt).

I just wish Graeme Smith were still with us to play this.

Rob Manuel’s British Council Tile / Bus Fabric Sim

Rob’s British Council Tile / Bus Fabric Sim — described here: Amstrad BASIC that approximates the tiling schemes that a local council might have used for a municipal building in the 1970s — is a joy. So few colours!

No, really: this *was* the seat pattern on Western SMT buses circa 1979

Because I care (and don’t if you don’t), here’s the Locomotive BASIC source, lovingly typed into the Caprice32 emulator then extracted as text using iDsk:


10 ' British Council Tile / Bus Fabric Sim
20 ' by Rob Manuel 2018
30 '
40 ' z/x - change char up/down (ascii)
50 ' space - random palette
60 ' c - show ascii val, inks & pause
70 ' v - random character (128+ ascii)
80 ' b - random char and cols
90 ' n - fill with same line & pause
100 'i - input ascii value
110 '
120 ON BREAK GOSUB 260:MODE 1:LOCATE 1,26
130 DEF FNs=INT(RND*255)
140 SYMBOL 255,FNs,FNs,FNs,FNs,FNs,FNs,FNs,FNs
150 DEF FNp=INT(RND*4)
160 DEF FNi=INT(RND*26)
170 GOSUB 470
180 GOSUB 270
190 o$="":i$=INKEY$
200 IF i$<>"" THEN GOSUB 380
210 FOR i=1 TO 40
220 w$=CHR$(14)+CHR$(FNp)+CHR$(15)+CHR$(FNp)
230 w$=w$+CHR$(c):o$=o$+w$:NEXT i
240 store$=o$
250 PRINT o$;:GOTO 190
260 CALL &BC02:PAPER 0:PEN 1:END
270 aa=FNi:bb=FNi:cc=FNi:dd=FNi
280 INK 0,aa:INK 1,bb:INK 2,cc:INK 3,dd
290 BORDER aa
300 GOSUB 320:RETURN
310 IF c>255 THEN c=32:IF c<32 THEN c=255
320 LOCATE 1,1:PAPER 0:PEN 1
330 PRINT "C:"c;
340 PRINT CHR$(c);
350 PRINT " ";
360 PRINT "I:"aa;bb;cc;dd;
370 LOCATE 1,26:RETURN
380 IF i$=" " THEN GOSUB 270:RETURN
390 IF i$="z" THEN c=c-1:GOSUB 310:RETURN
400 IF i$="x" THEN c=c+1:GOSUB 310:RETURN
410 IF i$="c" THEN GOSUB 310:CALL &BB18:RETURN
420 IF i$="i" THEN LOCATE 1,1:INPUT "ASCII?",c:GOSUB 310:RETURN
430 IF i$="v" THEN GOSUB 470:GOSUB 310:RETURN
440 IF i$="b" THEN GOSUB 270:GOSUB 470:GOSUB 310:RETURN
450 IF i$="n" THEN FOR i=1 TO 25:PRINT store$;:NEXT:CALL &BB18:RETURN
460 RETURN
470 c=INT(RND*128)+127:RETURN

And if you really care, here’s an emulator snapshot — BritishCouncilTileSim.zip

Update: I modified the code slightly (essentially, all INT(RND*n) to RND MOD n) so it would compile with Hisoft Turbo Basic. It works! It’s faster!

Snapshot: BritishCouncilTileSimCompiled.zip

Important research: was the Eudora “New Mail” chime from Ren & Stimpy’s “LOG”?

Inspired (obliquely) by this Metafilter post, I set out to answer a burning question.

LOG chime

This occurs from second 36 to second 38 of this video:

The chime when extracted without further processing, sounds like this:

(direct link: Original-Log-Commercial_The-Ren-and-Stimpy-Show.wav)

Eudora chime

I found a copy of Eudora Mail 1.44 for Windows (bundled up in an archive quaintly called “internet.zip”) here. The EUDOR144.EXE file is itself a Zip archive, and contains several files. The important one is WEUDORA.EXE (722,944 bytes; SHA256 checksum a35f2ef1e95242228381d9340fff0995f4935223f88a38b9200717107252dfb9).

This is a Windows 16 “New Executable” (NE) file, and I used panzi/mediaextract to scan and extract the RIFF/WAV data:

(direct link: WEUDORA.EXE_000a8200.wav)

They sure sound similar. But are they … the same?

Comparison

I made sure that both samples were set to the same rate, and I applied simple amplification in Audacity so that they both had a peak volume of -3 dB. Aligning the tracks as best I could, I got this:

Log audio on top, Eudora chime underneath

The Eudora sample is very slightly slower than the Log one. It might have been that the Eudora authors sampled the chimes from an analogue video tape. The match is remarkable, however, as they play together with only very slight phasing effects:

(direct link: Log_vs_Eudora-log_left-Eudora_right.wav)

Conclusion

Yes, the Eudora Mail “New Mail” chime did come from Ren & Stimpy after all.

Installing the Versatile Commodore Emulator (VICE) on Raspberry Pi

Updated 2020-11-28: thanks, Ennio! Should now build after new Raspberry Pi OS and Vice changes

As requested on our local Commodore user group mailing list, how to install VICE on a Raspberry Pi running Raspberry Pi OS:

sudo apt install autoconf automake build-essential byacc dos2unix flex libavcodec-dev libavformat-dev libgtk2.0-cil-dev libgtkglext1-dev libmp3lame-dev libmpg123-dev libpcap-dev libpulse-dev libreadline-dev libswscale-dev libvte-dev libxaw7-dev subversion yasm libgtk3.0-cil-dev xa65 libsdl2-dev libsdl2-image-dev libgtk-3-dev libglew-dev

mkdir -p src

cd src

svn checkout https://svn.code.sf.net/p/vice-emu/code/trunk trunk

cd trunk/vice

./autogen.sh

./configure --disable-pdf-docs

make -j4

sudo make install

This was freely adapted from the build docs, Linux-Native-Howto.txt, which has more info if you get stuck.


If you’re feeling fancy and want nice GUI controls and sound recording and menu stuff, try

./configure --disable-pdf-docs  --enable-lame --with-mpg123 --enable-shared-ffmpeg --enable-x64 --enable-native-gtk3ui --enable-desktop-files

This will give you desktop icons too. I’m not sure in the apt line is quite right, though — but I’ve had my doubts about all those CIL entries, ‘cos I think they pull in Mono/.Net, and who would want to use that?

importing Applesoft BASIC programs on the Apple IIe

Just what no-one has needed since about 1979 or so …

BASIC on the Apple II has no easy way to import text as a program. When you LOAD a file, it must be in Apple’s tokenized format. While Apple DOS has the EXEC facility to run script files as if they were typed from the keyboard, it’s very picky about the file format:

  1. There must be a carriage return character (CR, ASCII 13) before the first line
  2. All line numbers must have an extra space before and after them
  3. All tokens must be in upper case
  4. All tokens (keywords and functions) must have a space after them.

The right way to do this conversion would be to write a tokenizer that spits out the correct binary file. But you can (kinda) fudge it with this shell command, operating from BASIC source PROG.BAS:

sed 's/^[0-9][0-9]*/& /;s/^/ /;1s/^/\n/;s/$/ /;s/[:()]/ & /g;' PROG.BAS | tr '\n' '\r' | ac.sh -p EG.dsk PROG T

ac.sh is the command line version of AppleCommander, and the file EG.dsk referred to above is an Apple DOS 3.3 image created with

ac.sh -dos140 EG.dsk

It still needs work, as there are functions that will mess this up, and Applesoft’s parser makes a mess of code like IF A THEN …, turning it into IF AT HEN ….

So if I wanted to import the following futile program:

10 REM A FUTILE PROGRAM BY SCRUSS
20 HOME
30 FOR X=1 TO 20
40 PRINT SPC(X);"FUTILE"
50 NEXT X

Run through the script (but before EOL conversion) it would look like this:

 10  REM A FUTILE PROGRAM BY SCRUSS 
 20  HOME 
 30  FOR X=1 TO 20 
 40  PRINT SPC ( X ) ;"FUTILE" 
 50  NEXT X

Make a disk and put the modified program text on it:

ac.sh -dos140 futile.dsk
sed 's/^[0-9][0-9]*/& /;s/^/ /;1s/^/\n/;s/$/ /;s/[:()]/ & /g;' futile.bas | tr '\n' '\r' | ac.sh -p futile.dsk FUT T

Load the disk into your Apple II, clear out the init program, and import the code with EXEC FUT:

If all you get is ] cursors printed and no syntax errors, then something might be working. List it:

Run it:

Disk image: futile-AppleII-dsk.zip, containing:

$ ac.sh -l futile.dsk

DISK VOLUME #254
 T 002 FUT 
 A 002 FUTILE 
DOS 3.3 format; 134,144 bytes free; 9,216 bytes used.

Big old scanned manuals to small old scanned manuals

It is good that there are so many scanned manuals for old computer systems out there. Every old system did things its very own special way, and life’s too short to guess. I mean, there’s not much out there on the SYM-1 I’m trying to get working again:

— not much except for 6502.org’s excellent Synertek SYM-1 Resources, that is.

Some manuals, though, while lovingly scanned, are just too large to download, browse or file. Take, for instance, AppleIIScans’ Apple II BASIC Programming With ProDOS. It’s a very faithful colour scan, but at 170 MB for 280 pages, it’s a bit unwieldy. I suspect it’s Adobe Acrobat Paper Capture’s fault: while it makes turning scans into readable files really easy, it doesn’t warn against using 600 dpi full colour for a book with only decorative use of colour.

Good old Ghostscript saves the day, though:

gs -sDEVICE=pdfwrite -sColorConversionStrategy=Gray -dProcessColorModel=/DeviceGray -dPDFSETTINGS=/ebook -dNOPAUSE -dBATCH -dSAFER -q -sOutputFile=1983-A2L2013-m-a2-bpwp-grey.pdf -- 1983-A2L2013-m-a2-bpwp.pdf

By downsampling the scanned images and converting everything to greyscale, the result’s only 16 MB. All text and indexing from Acrobat is left intact.

Easy Raspberry Pi framebuffer screenshots with raspi2png

I gave a talk about retro-gaming on the Raspberry Pi yesterday. I was describing RetroPie, and I really needed lots of screenshots to illustrate games. I’m used to grabbing screens under X, but RetroPie runs without it, so all my usual tools were of no use.

I’d just found out about raspi2png, and it works really well! Usage is simple: just call it like

raspi2png -p outfile.png

and it’ll save whatever’s on the screen. It doesn’t play well with X, but there are already tools to take screenshots with that. As I was playing games, I didn’t want to have to pause the computer to take a shot, so I ran the command every five seconds for 30*5 seconds like this:

for f in {1..30}; do raspi2png -p retro_$(date -Iseconds).png; sleep 5; done

Here are some quality shots via raspi2png from Deathchase, officially the best ZX Spectrum game ever:

“The Error Message as a bourgeois construct”

If you try to run the (unmodified) BASIC code for Oregon Trail (1975) on PDP-8 BASIC, you get this:

 DI 30
 XC 45
 XC 205
…
 IF 700
 NM 730
… (many, many more lines …)

I thought at first it was a stack trace, but nope — it’s error messages! You need to dig through your trusty language manual, and on page 132 it has a table to explain:

DI ERROR IN DIM STATEMENT
IF ERROR IN IF STATEMENT
NM MISSING LINE NUMBER
XC CHARS AFTER END OF LINE

(and yes, they’re in all-caps. Mixed case? Mixed feelings!)

So whenever Python throws a tantrum (or as it calls it, an exception) and wails at length about its problems, remember PDP-8 BASIC: Two letters + a line number. That’s all.

The Pocket DEC Pretender (PDP) Zero

PDP (Pocket DEC Pretender) Zero: lettering came out a bit more, um,  artisanal than I’d hoped …

Digital (aka DEC) used to make some very solid minicomputers back when a minicomputer was fridge-sized and people were still building nuclear power stations to be controlled by them. The Raspberry Pi Zero is a very mini computer indeed, and in USB gadget mode running SimH it makes a nice little emulation platform.

The case is from Thingiverse: One Piece Raspberry Pi Zero + Camera Case (with GPIO) by Superrei, but with the DEC PDP logo in relief on the top.

DEC minis were famous for their arrays of blinkenlights. The Pocket DEC Pretender, not so much: it has one tiny green light that flickers a bit now and again:

PDP (Pocket DEC Pretender) Zero: case open, very few blinkenlights

But it’s a genuinely useful (for my values of useful) emulation platform. Here it is pretending to be a PDP-8, running BASIC under OS-8:

PDP (Pocket DEC Pretender) Zero: PDP-8 BASIC!

(background in case pictures woven in Toronto by Deftly Weft)

Apple II on Raspberry Pi

C’mon let’s all die of dysentery on the Oregon Trail!

Update: You probably want to use https://github.com/linappleii/linapple instead of Linapple-Pie these days.

Building and installing the linapple-pie Apple IIe emulator is relatively easy on the Raspberry Pi:

sudo apt install libcurl4-openssl-dev libzip-dev zlib1g-dev libsdl1.2-dev libsdl-gfx1.2-dev libsdl-image1.2-dev libsdl-sound1.2-dev build-essential git
git clone https://github.com/dabonetn/linapple-pie.git
cd linapple-pie/src
make
sudo make install

This also works on an x86_64 Ubuntu machine. It does also install on a PocketCHIP (even if it takes a really long time) but I can’t get the display resolution to fit correctly.

Fun things you learn from old computers …

The program on the left is running on the decimal interpreter, the one on the right the regular one

Microsoft used to supply two versions of its BASIC for Macintosh. One used decimal mathematics for precise tallying of small amounts. The other used the more familiar floating point mathematics, rounding errors and all. I don’t know what floating point library Microsoft used for sure — perhaps Motorola’s 32-bit Fast Floating Point system — but it introduces rounding errors pretty quickly. Modern routines don’t start displaying oddly until after 15 decimal places.

Consider this simple program:

10 LET x=36/10
20 LET a$="## #.#"
30 FOR n%=1 TO 18
40 PRINT USING a$; n%; x
50 LET a$=a$+"#"
60 NEXT n%
70 END

Along with the number of decimal places, it should print 3.6, 3.60, 3.600, 3.6000, … with an increasing line of zeroes after the 3.6. Bas makes a valiant but typical attempt:

 1 3.6
 2 3.60
 3 3.600
 4 3.6000
 5 3.60000
 6 3.600000
 7 3.6000000
 8 3.60000000
 9 3.600000000
10 3.6000000000
11 3.60000000000
12 3.600000000000
13 3.6000000000000
14 3.60000000000000
15 3.600000000000000
16 3.6000000000000001
17 3.60000000000000009
18 3.600000000000000089

Oddly enough, good old Locomotive BASIC on the Amstrad CPC does it more correctly somehow:

So the variables, they vary.

Spectrum is Green!

My previous adventures with my Sinclair ZX Spectrum 48K in Canada were not resounding successes. I couldn’t get the display to work, and tapes wouldn’t load well, so I’d been using Fuse while the hardware sulked in a cupboard.

I’d previously got a proper power supply (9 V DC, ≥ 1.4 A, centre negative) and bypassed the PAL UHF modulator to give composite video. No television, monitor or converter box that I had tried seemed to give a useful display.

Back in May, Walter Miraglia brought a tiny 7″ composite colour monitor to TPUG‘s Retrocomputing Night. He let me try it with the Spectrum, and it worked very well. Walter said it was an extension monitor for a car DVD player.

I dug around, and found that local surplus clearout store Tech Source Canada had the Philips 7″ portable DVD Player PD7016/37 for $60. This gives you two identical DVD players with composite input. I think my other one will be destined for a Raspberry Pi project somewhere.

To get these monitors running, you’ll need:

  • a 9–12 V DC power supply able to give ≥ 1 A. I use a regulated supply that gives 9.1 V open circuit and is rated at 2 A. Note that the power connector is slightly smaller than the common 2.1 mm barrel, so you may have to order this one, unless you can solder something up.
  • A cable like this 3.5mm Stereo to Composite Video + Audio Cable (3 RCA). These are sometimes just called camcorder cables. They use a 3½ mm TRRS jack, and can also — if you don’t mind not quite having the connectors in the right order — work with the composite/audio output of more recent Raspberry Pis. Tech Source had these for under $5.

Connect it up , and — success! Well, slightly qualified success. The screens do not have the greatest resolution, so pixels are slightly smeared together. The screens do have a decently fast refresh, and the whole look is just right. With its colour clash and dot crawl, nobody ever expected great video from the Speccy anyway.

Here are some screen shots taken with my phone, and a couple of pixel-sharp screenshots from Fuse to compare:

Moon Cresta - complete with authentic weird language
Moon Cresta – complete with authentic weird language

Moon Cresta — the same screen from Fuse
Moon Cresta — the same screen from Fuse

Moon Cresta - nice loading screen
Moon Cresta – nice loading screen

Manic Miner — a game I am not good at
Manic Miner — a game I am not good at

Manic Miner - perhaps the (deliberately?) worst game music ever
Manic Miner – perhaps the (deliberately?) worst game music ever

3D Death Chase — OH NOES A TREE!!!!1!!
Deathchase — OH NOES A TREE!!!!1!! Looks like the Riders of the Big Bikes just lost another member

Knight Lore
Knight Lore

Chuckie Egg
Chuckie Egg

Chuckie Egg from Fuse. We can't do anything about the attribute clash
Chuckie Egg from Fuse. We can’t do anything about the attribute clash

So I can now definitely view the screens. Huge thanks to Walter for tipping me off to these DVD players.

[Incidentally, the screens are designed for car use, so don’t stand up properly unless you get creative with some supports. I laser-cut these out of 3 mm plywood:

mini screen feet for 3 mm ply
mini screen feet for 3 mm ply. Cutting template PDF is linked underneath this image

Glue the little sticks on to the flat ends, and they’ll fit into the slots in the back of the monitor. Here are the feet with the sticks fitted:

screen feet with sticks glued in place
screen feet with sticks glued in place

There are better-designed feet than these, but they work, mostly.]

I was still having game loading problems. Try as I might, I couldn’t get anything to load reliably. Retrocomputing Stack Exchange came to the rescue, in the shape of mcleod_ideafix’s very helpful answer.  If your audio player is running from batteries and you can use a stereo cable, you can convert the normal mono loading audio into stereo with one channel inverted. This gives you effectively double the volume, and works quite well with my audio player, an old Edirol R-1*.

Inverted stereo loading data, showing 4000/8000 Hz speedload tones
Inverted stereo (or differential) loading data, showing 4000/8000 Hz speed-load tones

This audio will not load into an emulator, or work with a mono cable. Some audio players even render it as silence.

Here’s a script to take monophonic loading data and convert it to this faux-differential stereo format using Sox:

#!/bin/bash
# wav2differential.sh - convert mono game tape audio to 2× stereo
# usage:   wav2differential.sh infile.wav
#          (creates  infile-differential.wav)
# scruss - 2016-06-07
# method by ‘mcleod_ideafix’; many thanks / greetz
#   — https://retrocomputing.stackexchange.com/a/774/439

base="${1%.wav}"
sox -q --norm=-3 "$1" -b 16 "${base}-n.wav"
sox -q  "${base}-n.wav" "${base}-ni.wav" vol -1.0
sox -q  --norm=-0.1 -M -c 1 "${base}-n.wav" -c 1 "${base}-ni.wav" -c 2 -b 8 "${base}-differential.wav"
rm -f  "${base}-n.wav" "${base}-ni.wav"

If you want to check your audio levels, sox can also create the 800 Hz header tone used by the Spectrum. Run the output of the command below through the script above, load it onto your audio player and fiddle with the volume until the border flickers steadily:

sox -n -b 8 -r 8000 800hz-header.wav synth 30 square 800

Lovely loading bars ...
Lovely loading bars …

I was also looking for the games to load fairly quickly. Tapes used to take over three minutes to load, and while retrogaming all is about the experience, I haven’t got time for that. Fuse has some utility programs which will convert a .Z80 game snapshot into an audio file that loads in about 1¼ minutes.

To convert the snapshot to a speed-load TZX tape image:

snap2tzx -o game.tzx -s 3 game.z80

To convert that virtual tape image into audio:

tape2wav -r 16000 game.tzx game.wav

You can then run that WAV file through the stereo/differential script I listed above. Have fun!

Building the Stick of Joy

Update, 2017-06: I’ve updated the plans so you shouldn’t need to spend  time sanding things to fit.

Not-even-remotely over-engineered retrogaming joystickTracking down old Atari-style joysticks for retrogaming can expensive, and it’s hard to tell if you’ll get something reliable. So I made one for less than the cost of a used stick on eBay.

To build this, you will need:

  • 8-way joystick , or any stick compatible with the industry standard Sanwa JLF-P1 mounting plate. This has M4 holes at 84 × 40 mm.
  • Two concave momentary arcade push buttons. In my built, I used an older design that’s much taller. You could make the joystick box shorter if you used these snap-in buttons.
  • DE-9 (DB-9) Female Socket Connector
  • Terminal block, with at least seven connectors. You’ll likely want more, so this 12 position screw terminal block should work.
  • 4× M4 countersunk (oval head) machine screws with nuts and lots of washers. You’ll need washers to act as spacers between the box and the joystick mounting plate. This allows the joystick’s dust washer to move freely.
  • a couple of metres of 8-core stranded signal cable
  • hookup wire and spade connectors for building the button harness.

The case is made from 6.4 mm high quality plywood, using a template generated by BoxMaker.  The external dimensions of the box are 163 mm x 143 mm x 83 mm. I haven’t included any kerf width in the design, so the edges should fit together easily for gluing.

joystick-box
Joystick box plan for download: joystick-box-201706.svg (SVG: best in Inkscape); joystick-box-201706.pdf (PDF).

If you want to make your own design, here’s the top plate plan: joystick-box-top-201706.svg (SVG); joystick-box-top-201706.pdf (PDF).

The basic DE-9 pin wiring for Atari-style joysticks goes like this:

1 — Up
2 — Down
3 — Left
4 — Right
6 — Button
8 — Ground

There are many variants that add features to this scheme, however. If you’re building for a specific computer, Tomi Engdahl’s Joystick information page has the details.

Many thanks to Andrew Horsburgh for the use of Protolab‘s laser cutter.

LibreOffice brings the old

Twenty-two years ago, I wrote a thesis. It wasn’t a very good thesis, but it did what it needed to do. For years, its model files have been unreadable, because the spreadsheets were written in a ~1992 version of Microsoft Works. These are old files:

1993-04-21 03:19 newmodel.wks
1993-04-21 03:19 newmodel.wk1
1993-04-08 06:29 pr_fa.wks

Quite recently, LibreOffice realized that there are old files out there that (unlike my thesis models) could still be useful. As they have no commercial requirement to only support the latest and greatest, LibreOffice added the ability to read these ancient works. So my old stuff lives again:

ms works files from 1993

I found a screen dump that I used back in ’93 to illustrate the layout. The display was colour, but here it is brought back to life with a little bit of antialiasing:

'93 print stylee

LibreOffice can also read old AppleWorks files. Although Works 6 still runs on Catherine‘s Mac, it looks a bit … dated:

appleworks

Thanks, LibreOffice! It’s sometimes easy to forget (like right after updated to Ubuntu 15.04, which decided that BlueTooth support was kinda optional unless you jumped through hoops …) that people do write software just to be more useful.