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.

A conceptual design of the S1-AU Mk1
An early sketch of the S1-AU

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:

The S1-AU Mk1 proof of concept
The S1-AU proof of concept

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.

A Diagram of the S1-AU Mk1 system
A diagram of the S1-AU system

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:

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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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