Category Archives: Projects

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 »

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 – a different direction

[Eagle vs KiCad part 8] So, as I mentioned in the previous post, I’ve decided to change direction slightly. Rather than continuing with the HexMonitor project to a completed and fabbed board, I’m going with a slightly simpler project. The reasons are two-fold: first, the HexMonitor board is sufficiently complex that I figured it had no chance of working, this being… Read more »

Altair-Duino – the low-cost Altair 8800

I’ve wanted an Altair 8800 for a long time now. It’s not that you can do much with it. But it is such an important part of computing history. Famously, the January 1975 edition of Popular Electronics featured the Altair 8800. Or rather, it featured a non-working prototype. The first working machine had gone missing in the post. The magazine… Read more »

Fault finding: the aha! moment

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Well, maybe not so much aha! More like FFS. Weird as it sounds, debugging errors is one of the things I enjoy about both coding and electronics. I’m an amateur in both fields and waste little time on planning my projects. I prefer just to delve right in. Rather than sketch out a circuit first, for example, I just get… Read more »

Dreambox: change of plan

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Okay, so here’s a tip for anyone who, like me, prefers to make up their electronics projects as they go along – who simply doesn’t have time for all that planning and designing nonsense. Buy yourself a desoldering station. Seriously – buy it before you even buy a soldering iron, just to be safe. A quick recap: I decided that… Read more »