Tag Archives: parallel

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: 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 »

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: 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: 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 »

Getting to grips with the parallel interface

The Centronics interface seemed such an intrinsic part of a computer’s architecture that, to those of us whose computing coming-of-age was in the 1970s or 1980s, it seemed unimaginable that it would all but disappear. Who knew that serial interfaces would one day reign supreme? There’s something still very satisfying about hooking up a parallel connection, with fat cables and… Read more »