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# S1-AU Mk1: a 4-bit arithmetic unit

The S1-AU Mk1 is a 4-bit arithmetic unit, designed to help you explore the guts of computing.

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The S1-AU Mk1 is a beautifully engineered DIY electronic kit designed with classic 7400 series ICs. The kit works as an operational 4-bit arithmetic unit, similar to what was found in early computers. It can perform 4-bit binary addition, subtraction, accumulation and comparison.

Using ultra-bright LEDs the board shows you the state of each operation, step by step, so you can actually see and understand how a computer really works!

I started designing the ARITH-MATIC S1-AU Mk1 in late 2016 after a visit to the Museum of Computing in Swindon, England. Inspired by the computational objects on display, I sat down at a kitchen table late one evening and started building a 4-bit arithmetic unit from spare 7400 series ICs.

My idea was to design and build a mechanism which visually and aesthetically showed computation in the simplest form possible.

After creating a relatively unwieldy breadboard proof of concept (as you do in all great hardware projects), I've started developing a prototype PCB. You can read more about this here: http://arith-matic.com/the-soul-of-a-new-pcb

The S1-AU performs 4-bit binary addition, subtraction and accumulation using 74HC173 registers for temporary data storage and a 74HC283 full adder for binary calculations. A 74HC157 multiplexer is used to enable accumulation. The board also shows the result of logical operations (A=B, A>B, A<B) via the onboard flags. The flags and binary data used within the calculations are represented visually through onboard LEDs.

I started the ARITH-MATIC S1-AU project in 2016 and since then it has taken on a life of its own. Next is preparation for a crowdfunding campaign to release the S1-AU as a DIY hardware kit. I thought I'd share details of the board and progress on this page - as there is still a long way to go!

Here's a clip of the latest PCB prototype working in 'accumulation' mode:

• ### New ARITH-MATIC Kit Launch: S1-MU Mk1

Hello all.

Thanks to the success of the S1-AU Mk1 project, I'm excited to announce the launch of the second ARITH-MATIC kit: S1-MU Mk1.

The S1-MU Mk1 is an 8-bit memory unit, using the (excellent) LY62256PL SRAM IC and, of course, a few 7400 series ICs too!!

You can discover more about the kit here: https://arith-matic.com/products/electronic-kits/s1-mu-mk1

The S1-MU and S1-AU are both available via the ARITH-MATIC website, with shipping to the UK, EU, USA & Canada!

Finally, a bit thank you to everybody who has supported the project, either by sharing with others, providing feedback, or by purchasing one of the kits.

Cheers,

Richard

• ### ARITH-MATIC S1-AU Mk1: A belated update!

Hi all.

It has been a while since I've updated this project page. This has been for numerous reasons but mainly because turning a kitchen table project into an actual product is seriously hard work!

I'm really proud, however, that the S1-AU Mk1 has been successfully launched and is now available via our new website: https://arith-matic.com/kits

I'm currently writing a (rather long) post about this experience - everything I've learnt, the trials and tribulations of launching a maker product, the strange world of compliance testing, the brilliant people I've met on route and the continuous inspiration I have found from other TTL-esque projects - I'll link to it from this page when it's ready!

In the mean time, if you'd like to find out more about the S1-AU Mk1, or arithmetic units in general, why not check the latest ARITH-MATIC note: Arithmetic Logic Units (ALU): An Introduction.

• ### The colour of Blinkenlights, take 2.

Now the red LEDs have arrived, here's a fairer comparison. Yellow or Red?.. ( Yellow is winning in other places I've asked :).

• ### The colour of Blinkenlights

Thinking of shipping the S1-AU Mk1 kits with yellow LEDs - PDP-8/I style - rather than red... What does everybody think?

• ### S1-AU Mk1: Prototype Solderlapse

Soldered together the latest revision this afternoon (number 7!), and thought I'd experiment with my GoPro's timelapse mode.

• ### DIY Hardware: The Soul of a New PCB

Here's the second post I wrote for the ARITH-MATIC project: http://arith-matic.com/notebook/the-soul-of-a-new-pcb

• ### The Maker Spirit: From Kitchen Table to Micro Startup

Here's an introduction I wrote to the ARITH-MATIC project: http://arith-matic.com/notebook/the-maker-spirit

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## Discussions

Dr. Cockroach wrote 02/17/2018 at 21:14 point

Looks great and neat layout :-) I'll be watching and learning.

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ARITH-MATIC wrote 02/17/2018 at 13:10 point

Great - thanks for the comment Dave!

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Dave's Dev Lab wrote 02/16/2018 at 19:09 point

Great looking design and implementation! I will be looking for the kickstarter!

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