speculatrix

[speculatrix]

Dicom to weird animated GIF via Python

Every now and then, having some coding skills turns out to be useful in the most unexpected ways. In support of a creative project, I need to be able to convert some image files. But these aren’t your normal, run-of-the-mill snapshots. They are images captured during CT and MRI scans. This being France, your medical data is regarded as your personal property. Most times when you have a scan –…

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Repairing a BBC Master #3: Power checks

Repairing a BBC Master #3: Power checks

Now that we know the sickly BBC Master’s power supply is okay, it’s time to check whether that power is getting to all the chips on the board. Luckily, the schematics help us here in more ways than one. On the first page is a table of all the ICs with pin numbers for their VCC and GND connections. I have this printed out and on a clipboard for easy reference. I also have the schematic PDF…

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Prints, posters and more

Prints, posters and more - I've opened a new store on Redbubble to help support my blog.

In my other life, I’m a photographer. In fact, I’ve been taking pictures since I was a teenager and my degree is in film & photography. It’s deep in my DNA. Maybe being a geek helps. Photography is a combination of aesthetics and technology – now more than ever. Most of my work centres around landscape, the environment and travel, although I also specialised in aviation for a while. You can find…

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Zolatron: RTC, SRAM and SD board

After my fun with real-time clock chips (here and here) I figured it was time to add one to the Zolatron 64. But there was a catch. The previous experiments had involved microcontrollers with built-in SPI capabilities. That was something the Zolatron sadly lacked. Luckily, someone else has already come up with a solution. The 65SPI project by Daryl Rictor is a very easy way to add an SPI…

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Repairing a BBC Master #2: Basic steps

First, do no harm. Second, check the voltages. That’s how the Hippocratic Oath starts when adapted for electronics. If the device under test is not getting the proper power supply, then you can’t reasonably expect it to work. But there’s something I wanted to check, even before I apply power, and this turned out to be a learning opportunity. The BBC Master has many powerful connections. With the…

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Adventures with real-time clocks – part 2

Adventures with real-time clocks – part 2 #rtc #Arduino

The story so far: I’d been tinkering with an MCP795W20 real-time clock (RTC) chip and having a frustrating time of it. Weird things were happening. It seemed very finicky. I’d put part of the problem down to using a breadboard (still think I’m not entirely wrong about that). It turns out, however, that the biggest problem was my own stupidity. I’d used entirely the wrong values for the load…

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Repairing a BBC Master #1 – plan of attack

Repairing an #Acorn #BBC Master, part 1 – plan of attack #retrocomputing #bbcmicro

So my poor Acorn BBC Master Turbo is sick … again. And I feel a little bit responsible. Quick recap: the Master developed a problem some years ago. This was ‘fixed’ when a very generous person donated a motherboard from his machine. I never did find the cause of the problem. Since then, however, the machine has spent a lot of its time stored in a cupboard because … reasons. The other day I…

[speculatrix]

Adventures with real-time clocks - part 1

Adventures with real-time clocks - part 1 - adding an RTC to my homebrew computer.

So I decided that I’d like to add a real-time clock (RTC) to the Zolatron project because … why not? Should be easy, I thought. Lots of people have done it. All I need is the right chip. Maybe that’s where I made my mistake. MCP795W20 RTC pinout As it turned out, for some reason, I already own three copies of the Micrcship MCP795W20. Why I have these and how long I’ve had them are mysteries to…

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IoT phone home

#IoT phone home - snooping on my #network to see what my devices are saying to their overlords

The Internet of Things (IoT) is very handy. I enjoy being able to adjust the lights in my living room just by talking to Siri. Or having lights turn on and off at set times of the day. But as we all know, IoT devices don’t just talk to us. In order to work, they need to communicate with all kinds of servers. And so I wanted to know what my devices are saying, and to whom. You would expect a lot…

[speculatrix]

Now available on Mastodon

I've made the move to #Mastodon - @speculatrix@mastodon.online. See yoou there!

As it happens, I set up my Mastodon account some time ago, long before Elon Musk’s ego decided it needed a new toy to destroy. I just hadn’t used it much because … well, I didn’t use Twitter much either. However, all the kerfuffle over Twitter has prompted me to look again at Mastodon. You can find/follow me at: @speculatrix@mastodon.online Hope to see you there.

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Zolatron 64 6502-based homebrew computer: mission accomplished

Zolatron 64 #6502-based #homebrew computer: mission accomplished

Okay, so I’m going to call it. This project is finished. Well, not finished exactly. No project is ever finished. You can always do more. And so it is with the Zolatron – I have ideas and plans that will keep me happily tinkering away for years. But I’ve met my main objective – which is to better understand how computers work. I’ve gained insights into subjects like hardware addressing and…

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What's better than a 6502 homebrew computer?

What's better than a #6502 #homebrew computer?

Yep, you guessed it – two of them. One of the side effects of ordering PCBs from the likes of JLCPCB is that you have to order at least five copies of each board. This doesn’t quite mean that I have enough PCBs to make five Zolatron 64s. For one thing, each of the machines above uses two of the 65C22 VIA boards (one for controlling the LCD and some LEDs, the other as a user port and user timer).…

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Zolatron 64: Writing an OS for a 6502 homebrew computer

Zolatron 64: Writing an OS for a #6502 #homebrew computer

I’ve said it before and I’ll say it again: I have no idea how you write an operating system. Even though I’ve sort-of written one. The Zolatron 64 6502 homebrew computer project started as idle curiosity that just got out of hand. I figured I’d be happy if I could get as far as writing ‘Hello world’ to an LCD display. But things then snowballed. All of my early code was what you might describe…

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Zolatron 64: memory expansion

Zolatron 64: adding a memory expansion board #6502 #homebrew computer

Things are continuing apace with the Zolatron 64 6502 homebrew computer. In fact, progress has been so rapid that I haven’t really had much time to talk about it. So here’s a quick refresher – and details of the new memory expansion board. Serial killer The 6551 ACIA serial board is dead. Well, it’s not dead, but I’ve stopped using it. As I mentioned in the last update, I now have another serial…

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Elliott 405 - basic principles

Elliott 405 - basic principles #vintagecomputing #retrocomputing

This selection from ‘Big Doug’ Selway’s trove of documents on the 1950s Elliott 405 mainframe computer takes us right back to the basics. First up is a ‘functional block diagram’ of the system. And what I find interesting about this is: How basic it is. Computers were really quite crude beasts back then. How it was felt you needed to know this stuff. Of course, you’ve always needed to know this…

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A newbie's introduction to CUPL and CPLDs

A newbie's introduction to #CUPL and #CPLDs

When you’re dealing with computer logic, things can get very complicated very fast. This is especially true when it comes to address decoding. You can easily find yourself tangled in a messy web of AND, OR, NAND and NOR gates. And there’s a problem you can run into when stringing together a bunch of logic gates – propagation delay. It takes a measurable amount of time for a chip to convert input…

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Zolatron 64: a bug hunter's diary

Zolatron 64: a bug hunter's diary. Learning lessons when hunting problems with my #6502 #homebrew computer

It’s always a good day when you get a package from the fab. There’s something simultaneously exciting and daunting about unwrapping a shiny new batch of PCBs. On the one hand, there are the possibilities promised by the new device. On the other, you’re wondering whether you made some kind of mistake in the design and if the thing will work. Short answer: no. My latest batch of boards from JLCPCB…