Author Archives: Machina

Zolatron 64: initial thoughts on a front panel

Any self-respecting retro-style homebrew computer needs two things – switches and blinkenlights. Otherwise, why bother? I haven’t got a working computer yet but already I’m thinking about a front panel for it. This will be inspired, to some extent, by the Altair 8800 and also by the PDP-8, both of which I have in the form of modern replica kits…. Read more »

A PCB virgin no longer

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Well, it’s happened. My first PCBs have arrived. Now it’s just a matter of summoning the courage to solder on the parts and see if it works. This is the board I designed as part of my Eagle vs KiCad series. It breaks out a Centronics-compatible DB25 socket, with the data lines being driven by a shift register. There’s a… Read more »

Debouncing fun with Schmitt triggers and capacitors

You simply can’t trust switches. You think they’re either on or off, but the truth is that, in getting from one state to the other, they can change their mind many times. This is a phenomenon known as switch bounce and it happens because switches aren’t perfect. Just at the point where they are making or breaking contact, certain mechanical… Read more »

Zolatron 6502 homebrew computer – clocking in

Sometimes the things that confuse you most turn out to have the simplest solutions – and so it was with the clock for my Zolatron 6502 homebrew computer. First, let’s deal with the 6502’s clock pins. There are three of them and they’re called PHI1O, PHI2 and PHI2O – except when they’re not. Older versions of the 6502 have PHI1… Read more »

Epson MX-80 Part 4 – ESR check of the dodgy caps

It seems strange that both the capacitors and the transformer – the chief suspects in the investigation as to why my Epson MX-80 F/T III dot matrix printer belched out smoke – tested fine with a multimeter. As far as the capacitors were concerned, I measured resistance directly across their leads (having removed them from the circuit board) looking for… Read more »

Zolatron 6502 homebrew computer – a few tweaks

Within a couple of hours of posting the schematic for the main board of my Zolatron 6502 homebrew computer the doubts had already started to set in. I made the mistake of visiting Grant Searle’s site. I’m already familiar with his work having built one of his projects (an FPGA-based CP/M computer), and so I know he’s forgotten more than… Read more »

Zolatron 6502 homebrew computer – main board

Well, things are finally happening and I actually have a schematic for the main board of the Zolatron 64 6502-based homebrew computer. I’m not saying it’s a good schematic. And I’m certainly not claiming that it will work. But it passes the Electrical Rules Check and I don’t think I’ve missed anything out. So that’s an achievement in itself. Click on… Read more »

Zolatron 6502 computer: decoding the RAM more reliably

In my earlier post on address decoding logic, I mapped out a fairly simple way of dividing up the 64k address space for my 6502-based retro computer. But maybe it was too simple. There is one slight complication – easily fixed, but which will require the introduction of another chip. And the reason for this is something lacking in memory…. Read more »

Zolatron 64 6502 computer: the backplane dilemma

Having looked at a lot of homebrew computers online, including the popular RC2014, it seemed obvious that the best way of going about my own project is to opt for a backplane design. But maybe it’s too obvious. Just as I was ready to get started with designing the Zolatron 64 I stumbled across this page (via the excellent 6502.org… Read more »

Epson MX-80 Part 3 – well, this is strange

And so to the next instalment of trying to get my Epson MX-80 F/T III dot matrix printer back up and working. Previously on Epson MX-80… Just over a year ago, lots of smoke came out accompanied by a crackling noise. I’ve removed the main smoothing capacitors from the PCB and tested them. They seem fine. I tested the transformer…. Read more »

Epson MX-80 Part 2 – out damn cap

Time for the next step in my attempt to bring my beloved old EpsonMX-80F/T III dot matrix printer back to life. But first, some pictures of gorgeous old retro components. As we’ll see, they might be all I have left. I do love old resistors. They have so much character. And look how thick the wires are. There’s also a… Read more »

Epson MX-80 Part 1 – resurrecting an old friend

It’s hard to lose an old friend with whom you’ve shared more than a  third of a century’s worth of experiences. I’ll never forget the day it happened. I heard a coughing, spluttering noise, turned around and, sure enough, smoke was pouring out of the printer. And not just any old printer – my trusty Epson MX-80F/T III, the first… Read more »

Serial to parallel the hard way

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I kind of miss making hard copies of my program listings on a dot matrix printer. There’s something contemplative and satisfying about waiting for the printer to finish its buzzing and chattering so that you can pore over the code and find that bug. Also, printouts on continuous listing paper with holes down the sides feel like real computing. It… Read more »

PCB design: Eagle vs KiCad – the verdict

[Eagle vs KiCad part 11] Well here we are, the end of the road. Somehow I always knew this series would go to 11. I have, finally, made a decision which EDA – Eagle or KiCad – I’m going to use. It wasn’t an easy choice. Ground rules Let’s get a few things out of the way first, so you know… Read more »

PCB design: laying out the board with Eagle

[Eagle vs KiCad part 10] This is going to be a fairly short post because most of what I have to say can be summed up with: Eagle’s board layout program works very well and I had very few problems. It also offered very few features I wanted that KiCad didn’t. To create a board that will sync with your schematic… Read more »