Fun with chips: #1 MC1441 bit rate generator

I’m easily pleased. Leave me alone with a breadboard, multimeter, oscilloscope and a previously unencountered IC, and I can amuse myself for hours. Well, minutes anyway. It’s fun to fire up a chip and watch it do its stuff. And even more fun if it’s an old chip. But before we get to the IC itself, let’s fill in some… Read more »

SmartParallel: laying out the PCB

We’ve been here before, but now it feels like we’re finally getting somewhere. The long-running saga that is my SmartParallel serial-to-parallel dot matrix printer interface is nearing completion. Well, maybe. Having solved (I think) the back-powering problem, and with a prototype that I believe actually works, I’ve decided to call Rev 2.0 of the design schematic the final version. All… Read more »

ATMEGA328PB breakout and prototyping board

The first thing I did when I progressed from Arduinos to programming Atmel 8-bit microcontrollers in the raw was build a programming and prototyping board. [BTW, for once, this is not going to be a multi-post project. I’m putting a bit of background here, but will put full, constantly updated details on the GitHub page.] Arduinos make it easy for… Read more »

DIY joystick for the BBC Micro – part 6 – completed (definitely)

Just when you thought it was over… When we last saw this project it was complete except for stuffing the joystick into some kind of box. As that kind of mechanical stuff doesn’t interest me greatly (and I’m crap at it), I wasn’t going to bother with a post about this final step. But hey, I’m nothing if not a… Read more »

SmartParallel: curing the back-powering problem

And so back to the back-powering problem on my ever-imminent SmartParallel interface board. The issue is that, when the printer is powered on but the SmartParallel board isn’t, voltages coming from the printer via signal lines being held high are part-powering the board. One option was to simply ignore this problem. I find that works for a lot of things… Read more »

DIY joystick for the BBC Micro – part 5 – completed (pretty much)

Having got impatient waiting for my PCBs to arrive from China, I went ahead and cobbled together some interim solutions for this project. And what happens? The PCBs arrive the next day. These are the ‘fixed’ PCBs with the proper footprint for the DB15 connector. And what can I tell you? They work. There is one slight issue that I… Read more »

DIY joystick for the BBC Micro – part 4 – a quick lash-up

While waiting for revised PCBs to arrive from China, I figured the time would be well spent learning a little more about the BBC Micro’s analogue port. And I have taken delivery of a couple of DB15 breakout boards, which meant I could try wiring up the joystick, albeit in a crude and temporary way. One joystick needs to send… Read more »

SmartParallel: mystery solved

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Although the stripboard version of the SmartParallel board is working, one niggle remained. When the printer was switched on, but the SmartParallel board wasn’t powered, I was getting random resets of the printer. They weren’t as frequent as with the breadboard prototype, but they were there, sometimes. Also, there was a problem with signals effectively ‘back powering’ (I’m not sure… Read more »

SmartParallel: stripboard prototype – now with blinkenlights

Okay, so the next stage of the stripboard prototype for the SmartParallel serial to parallel printer interface went well. Mostly. As planned, I added a bar LED block with eight segments to show the state of the data lines, along with power-limiting resistors in the form of a resistor array. I also added four LEDs. Three are driven via a… Read more »

SmartParallel: stripboard prototype

Things went from bad to worse with the breadboard prototype of the SmartParallel serial to parallel printer interface. All was fine for a while. Lines of text sent from my Mac via an FTDI cable were duly printed on the Epson MX-80 F/T III dot matrix printer. But then, every now and again, the printer would randomly reset. After a… Read more »

SmartParallel: pulling up and pulling down

It’s never a good idea to let signals float around in the no-man’s land between the high state and the low state. This is why we so often use pullup and pulldown resistors. You set the line to a known, definite state by default and then switch it as necessary. Some uses of pullup and pulldown resistors are obvious. Some… Read more »

DIY joystick for the BBC Micro – part 3

Ah well, another valuable lesson learned. The PCBs for my homemade joystick, designed to work with the BBC Micro and Master, should have been very simple. They are very simple. And yet I still managed to screw up. The PCBs for both the main adapter, which plugs directly into the computer, and the connector for the joystick arrived the same… Read more »

SmartParallel: breadboard prototype

A major reason for doing breadboard prototypes is to learn what mistakes you’ve made in your circuit design. Of course, it’s also a way to introduce brand new errors. Or both. Before committing to fabricating PCBs, I wanted to check out whether my design for the SmartParallel dot matrix printer interface would even work. My confidence was reasonably high because,… Read more »

SmartParallel: hacking a Centronics connector

Okay, I lied. Having ordered the PCBs for my Centronics breakout board, and also having ordered a couple of DB25 breakout boards via Ebay, I settled in for the long wait I knew would follow. I said in an earlier post that I was getting used to these two to three-week delivery times for stuff coming from China. The truth… Read more »

Protip: Buy only female-female jumper cables

Jumper cables with DuPont headers are an essential part of your toolkit. Any dabbler in electronics will have drawers of the damn things – and probably not a few wandering randomly around the workbench. But when the time comes to buy more (where do they go?) there’s always a dilemma. Do you need male-male, female-female or female-male? And how many of… Read more »