Twice now I’ve declared my SmartParallel project completed, and twice it has proven to be faulty – or, at least, difficult. I’m still plugging away at it (more on that soon), but in the meantime I really wanted to be able to print out 6502 assembly code listings on my Epson MX-80 F/T III dot matrix printer. And then I… Read more »
Well, it had to happen sometime. I finally killed a Raspberry Pi. Not on purpose, of course. I’m not a psycho. (I’ve been tested.). Nope, it was just sheer impatience and stupidity. But we’ll get to that in due course. First, let’s talk about finishing a project that was already finished. Just when you think you’re out… Sometimes you think… Read more »
Well, it does seem that the problem I’ve been having with the SmartParallel board is indeed that horror of horrors – the intermittent fault. Or perhaps something weirder. This is some kind of quantum device – it works only when being observed. Setting up a server The SmartParallel was working perfectly for a few days. Then I didn’t use it… Read more »
Hmm… maybe I spoke too soon. No sooner had I congratulated myself on a completed project than a problem raised its ugly head. And it was one that required some tracking down. And so, as this blog is my lab notebook, I thought I’d share what happened, as I always find other people’s tales of troubleshooting to be illuminating. One… Read more »
It’s done. For now. After weeks of dithering, I finally got around to making up one of my SmartParallel serial-to-parallel printer interface PCBs. I chose to solder the components – mostly surface mount – by hand and that went easier than I expected. The only snag was that it didn’t work. Not right away, at least. And finding out where… Read more »
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 »
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 »
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 »
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 »
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 »
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 »
Creating a full breadboard version of the SmartParallel board is turning out not to be a five-minute affair. It has to be done meticulously and methodically if it is to have any value as a prototype. Fitting it all on to a single breadboard is proving challenging too. And that got me thinking. What about replicating at least part of… Read more »
The DottyMatrix project began when I thought, ‘It would be nice to make use of my old Epson MX-80 F/T III dot matrix printer’. The problem was talking to it. But then I thought, ‘It’s just parallel printer interface. I’ll make a microcontroller-based device to act as an interface. How hard can that be?’. The answer, it turns out, is… Read more »
Although it was gratifying (and surprising) that my DottyMatrix serial-to-parallel interface worked as soon as I plugged it into an actual printer, there was one nagging flaw. And that was a lack of acknowledgement. The /ACK signal in the Centronics interface was often sadly neglected, if not ignored completely. But in theory, the sequence for printing a character goes like… Read more »
It seems the repairs to my venerable Epson MX-80 F/T III dot matrix printer did actually work because it’s now printing again! What’s more, it’s printing via the prototype of my DottyMatrix serial to Centronics parallel interface. Time for a quick recap. The DottyMatrix is based around an AVR ATMEGA328PB microcontroller. It takes input on a TTL-level serial connection and… Read more »