Today, I’ve had an eventful day – not only have I received my small, test order from RS Components, I have also received the Nixie tubes and power supply boards. We chose to order 16 Nixie tubes – five for each 8-bit input register and six for the output register. Separate flyback boost converters are needed for the Nixie tubes as they operate at 120V which we are unable to supply directly.
I have yet to power up the tubes, but I’ll be sure to post some pictures when I do – they should give the TwitALU that vintage feel that we’ve been after. Continue reading →
Now that we have a Twitter Arithmetic Logic Unit, we can begin the fun stuff! Although 7400 logic is a classic platform for logic circuits, there is still an air of mystery about what goes on inside those little black chips. The advantage of 7400 logic is that it’s incredibly easy to use and the variant that we’ve chosen (74HCT) is super speedy.
But don’t worry, the Twittithmetic Logic Unit (TLU) isn’t just a PCB with a few black boxes. The core aim of the TwitALU project is to make computing rhythmically audible and visually entertaining. This is where the adder module comes into its own.
Musical references aside my time has, since building as much of the actual system on breadboard as was needed and ordering PCBs, been spent mostly on finding a suitable Python 3 compatible Twitter library and getting it to work.
Job number 1 was finding one I liked the look of. Truth be told, this extended as far as some Googling and finding a list of popular libraries. Then choosing one that was actively maintained, worked with Python 3 and introduced the least interfering with data between me and the actual Twitter REST API 1.1.
Since software has been a major focus while the PCBs have been in production we will give you a sneak peek into how we’re designing and keeping track of things.
Work in progress system class diagram
Above is our UML (Unified Modelling Language) class diagram for the software that is being developed on the Raspberry Pi. With a project as complicated as ours, it was very important to plan the software. This allowed us to break up the overall goal into smaller, more manageable modules. These modules could then be programmed in parallel as the requirements of each piece of code was predetermined. Continue reading →
Back in March 2013 a house-mate, Jeremy and I took part in the Bristol Mini Maker Faire representing Hack Kids where we had the task of using our skills to produce an interactive electronics project that would inspire young people to enter the world of electronics.
After investigating the 6502, Jeremy and I discovered that this ancient processor was still a complex beast of a machine with lots of constituent components and some quirky ways of implementing some features (like the extensive use of gated registers on the output of each combination logic block). The complexity of the 6502’s ALU means that implementing it entirely in large relays is unrealistic. It would be large, costly and the power requirements would be immense.
7400 logic NAND
Instead, we have decided to do what many other 6502 replica makers have done and construct the processor in 7400 logic first. Continue reading →
Before I tell you about the juicy guts of the 6502 microprocessor, let me introduce myself and tell you a bit about the people behind the project.
My name is Jaimesh Mistry and I am a fourth year Electronics and Communications Engineering student, studying at the University of Bristol. I’ve been ripping apart electronics and changing the way they work ever since I got my first RC car and went exploring in my dad’s crazy toolbox. These days I’m building all sorts of wacky projects with the skills I’ve gained at university – from autonomous robots to central heating systems that you can control from your smart phone. Hacking consumer tech is one of my passions, so a project like this where we mix a range of technologies from a range of eras in computing is right up my street.
Jeremy Dalton completes our duo and is also an Electronic and Electrical engineer in training at the University of Bristol. Like me, he is into all sorts of software and hardware hacking, has ‘tweaked’ many a working thing until it stops working and we’ve successfully collaborated on a good few projects in the past. However, one of his growing passions is in dirty great power electronics and motor drives, which recently landed him on an episode of Channel 5’s Motor Morphers where he helped convert a two-tonne milk float into a rubber burning dragster!
Anyway, enough about us. As promised, I’ll walk you through the MOS Technology 6502, why we chose it over other classic processors and our simplified design for implementation in 7400/relay logic. Continue reading →