Category Archives: DottyMatrix

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 »

SmartParallel: Centronics breakout board

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 »

SmartParallel: fixing the PCB layout

Hmm, yes, clearly it wasn’t going to be as easy as all that. While creating the PCB layout for the SmartParallel serial to parallel printer interface, I shuffled a few of the pin assignments on the Atmel ATMEGA328PB microcontroller. The reason was simply to make routing a tad easier. But I had a nagging feeling that this might cause a… Read more »

TTL serial level shifter

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Not every device speaks the same voltage. In designing the SmartParallel serial-to-parallel printer adapter, I chose to use 5V as the VCC supply throughout the board. But I was constantly aware that some of the devices that might talk to the board – such as the Raspberry Pi – use 3.3V for their I/O. What to do? There’s only a… Read more »

SmartParallel: First complete PCB layout

Well that wasn’t easy. Finally, the SmartParallel TTL serial to parallel printer interface has a complete PCB layout. And I learned a few lessons along the way. The most important of these, perhaps, is that when assigning signals to the pins of a microcontroller during the schematic drawing part of the project, don’t rely on whimsy or the luck of… Read more »

SmartParallel: refreshing the design

The SmartParallel, aka DottyMatrix, project has been languishing for a while now, but it’s time to get it restarted. SmartParallel is a serial-to-parallel interface that I embarked on because I wanted to be able to use my decades-old Epson MX-80 F/T III dot matrix printer with a number of platforms that don’t have parallel interfaces, such as the Raspberry Pi…. Read more »

DottyMatrix software stack: PHP & Python messaging

On the Raspberry Pi that I’m using to control my DottyMatrix serial-to-parallel Centronics printer interface there are two main software components – a web-based PHP/JavaScript front-end UI and a back-end server programmed in Python. So these need to talk to each other. Here’s the overall architecture of the solution: The matrixSvr.py program is intended to run permanently on the RPi… Read more »

DottyMatrix software stack: the front end

It’s one thing building an interface – it’s quite another working out how to use it. My DottyMatrix serial-to-parallel device is designed to drive my venerable old Epson MX-80 F/T III dot matrix printer (although it should work with any printer using a Centronics parallel interface). So far, I’ve mostly spoken to it using a terminal, sending text directly from… Read more »

DottyMatrix: a simple solution?

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 »

DottyMatrix: A simple acknowledgement

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 »

DottyMatrix: Printing to an actual printer

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 »

DottyMatrix: It’s alive!

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My old, beloved Epson MX-80 F/T III dot matrix printer is back in the land of the living. For now. As you can see from some of my earlier posts, I’m designing a serial-to-parallel interface with Centronics compatible DB25 connector so that I can print to my Epson from anything with a TTL serial port, such as a Raspberry Pi…. Read more »

DottyMatrix: ghost of the typewriter and the curse of the carriage return

In designing my DottyMatrix serial-to-parallel printer interface, I had to decide how it would handle the incoming data stream. The purpose of the DottyMatrix is to connect my venerable Epson MX-80 F/T III dot matrix printer to (probably) a Raspberry Pi so that I can print out text files, such as program listings. Obviously, it would be good if it… Read more »

DottyMatrix and Virtual Printer – together at last

It’s great when a plan comes together. Having independently played around with my DottyMatrix serial-to-parallel printer interface and the Virtual Printer (designed to simulate my still-dead Epson MX-80 F/T III dot matrix printer), it was time to hook them together. And it worked! On the left is the DottyMatrix using my prototyping board for the ATMEGA328PB microcontroller. Its serial port… Read more »

Virtual printer & more fun with AVR interrupts

In building my AVR ATMEGA328P-based ‘virtual parallel printer‘, there were two signals that required special treatment. So it was time to revisit interrupts. On a Centronics-style parallel port, the host machine sends an ‘init’ or reset signal to the printer to tell it to flush its buffers and set itself to the default state. It also sends a ‘strobe’ signal… Read more »