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Home-made real keyboard for ZX81

A ZX81's keyboard is frustrating to use. Especially for games. One too many times, you find your finger isn't quite over the pad when you have to make that crucial jump...

It's easy to use an emulator, but personally I don't get the same buzz.

My first computer, probably in '82 was a secondhand ZX81 which had been screwed to a board along with some kind of aftermarket keyboard (which really wasn't very good).

So for that reason I feel perfectly OK about sorting myself out with something similar now.

After looking at many options (including the ZX-Key, which looks excellent and the Minstrel keyboard which has tactile switches) I noticed while recapping a Spectrum +2 that the keyboard connections are very similar to the 81's:
There are more lines because the later spectrums have many more keys. But some study of the matrix diagrams made me think that they were compatible* if you take the first five and the first eight lines from those ribbons.

I *really* like…
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Getting a great display from a ZX81

The ZX81 was my first computer. Mine was screwed to a board with a terrible external keyboard, and I was proud of the fact that someone had fitted 2k of RAM.

It was my introduction to BASIC and machine language. Let's not forget that the humble zeddy is a vehicle for a Z80 (which has 16-bit features) running at >3Mz. (Of course you can only harness that amazing power in fast mode, ie without display output, because much of the CPU time is usually used to generate the display.)

Other than buying some kind of box that will convert the TV signal (with which I had limited success), it's possible to perform surgery to convert the output to composite, which modern displays may be more likely to display (but still maybe not in the case of the ZX81s with the older ULA).

Here are three methods - rewiring (cost zero), using some simple components (cost pence) and a purchased modification (still less than a tenner.)

With the newer issue 81 it's possible to simply tap the signal be…

Internal SD2IEC installed

My 'bionic' C64 has reached another milestone.

I wrote about it after I'd installed a PLAnkton, ARMSID and TOLB, and in the process resurrected a 'black-screen' computer.

Although I have an external SD2IEC which is good for plugging into any C64, Vic20 or C16 that I am using, I'd always intended to put an internal SD card drive inside this machine,

I had envisaged simply leaving the drive inside the machine, opening it up whenever I wanted to copy anything to the card.

But I found that Gaz Marshall has designed a replacement side panel for the C64 which has an SD card slot and houses the SD2IEC.

It's available as a model for 3D printing, or ready-printed direct from his Shapeways shop. I hadn't found the shop for ordering the printed version, so I asked a friend to print one for me.

Here's the result. Note that there's an all-in-one version, and a 'modular' version where you have to screw the tray to the side panel.
I found that some har…

Comparing ARMSID and real 6581 SID

I've set up a YouTube channel for posting my music, mostly to give myself an incentive to keep writing and hopefully improve those skills.

I recently posted a version of this eastern-sounding piece rendered by the notation software. An exercise in using the pentatonic minor for that eastern flavour.

I've now made recordings of the C64 playing the piece. First of all I made a 3-voice version (not yet posted) and then an 8-voice version using multi-tracking.

That's the first version you hear in this video, played on my 'bionic 64' which is fitted with an ARMSID.

Curious about how this would compare with the same music played by a real 6581 SID, I did the same recording using an all-original 64 and made a video with one recording after the other. My observations are below but judge for yourself.

In the 'pure' tones it's hard to hear a difference. But there is definitely a difference when there are many voices playing together and using pulse-wave modulatio…

Homebrew game for C64 - part something.

Progress has been slow, I've been caught up in ironing out a few problems. Debugging those was tiresome, which meant that I found it easy to do other things instead.

But now we have smooth scrolling background, music, enemies that scroll in from the left at an angle (hopefully soon multiple enemies / collectibles) multiplexing sprites (the sheep are each made of two sprites, a multicolour and a hi-res outline overlaid. The clouds are also sprites).

The bionic 64 project

Once I'd started writing a game for the C64 and started playing some of the great new games available, I decided that I needed a 64 that I can switch on and use as much as I like without worrying about stressing 35-year-old components (at least one of which is destined to fail in time).

Emulation is fine, in fact when I'm spending a lot of time playing one game I like to use all of the mod cons; big chair, big screen, Duoshock controller and VICE which makes loading up and saving the game at any point a breeze.

That's not the same as switching on a 'real' 8-bit computer and playing a game from the time.

I had a 'black screen' C64 and so there was an opportunity with a few options. Fit the original case / keyboard with a Pi, or with one of the modern boards - Ultimate 64 or C64 Reloaded

These boards are new boards which emulate the original components. So we're still talking emulation, albeit hardware rather than software. In the case of the Reloaded, y…

Homebrew game for C64 part 7 - revival

Revival of the project, that is. It's not a resurrection-based game.

Following a hiatus due to realising that my original concept was rubbish, I had a different idea. It's nothing particularly original; sideways scrolling, and the sheep following one another like a snake. There will be things to collect, and things to avoid.

Avoiding the enemies will be more difficult, the more sheep are following the one you're controlling. The idea is that you start with one, and accumulate friends as you go along.  They may be dispatched by enemies, and there will be a maximum of four because of the way I've used two sprites to get hi-res with multicolour effect.

There are no collectibles or enemies yet, but here's the basic action, which I'm really happy with.

The sound you hear on the video is being played by a breadbin 64. It's my most recent tune for this game. The video is captured from VICE

It was my first go with the 64's scrolling capability. I cut my teeth o…