Series 1 · Arithmetic Unit
Our pre-production S1-AU PCB

What is an arithmetic unit?

An arithmetic unit enables computers to perform binary arithmetic. It is one of the most important parts of a CPU (Central Processing Unit). An arithmetic unit which also performs bitwise logical operations is commonly referred to as an ALU (Arithmetic and Logic Unit).

Introducing the ARITH-MATIC S1-AU Mk1:

The S1-AU Mk1 is a beautifully crafted DIY electronic kit designed with 7400 series logic chips. It enables you to build a simple 4-bit arithmetic unit and manually perform simple binary operations.

The kit is a pragmatic introduction to computational hardware and an excellent soldering exercise for computing enthusiasts, hobbyists and makers.

Using 74HC173 registers for temporary data storage, a 74HC283 full adder for binary calculations, and a 74HC85 comparator for logical comparisons, the assembled board enables an operator to perform 4-bit addition, subtraction, accumulation and comparison.

Functional Diagram of the ARITH-MATIC S1-AU Mk1
Functional Diagram of the ARITH-MATIC S1-AU Mk1

Input into the unit is performed manually through an array of push button switches and binary operations can be traced through a series of on-board ultra bright LEDs.

The S1-AU Mk1 is powered via a USB mini cable, however it is not programmable - it requires manual operation through on-board switches. The USB cable is only used to deliver power to the unit, so you don't need to rely on batteries.

The kit contains all the through-hole components you’ll need to build your own 4-bit arithmetic unit and includes:

Kit Contents

  • S1-AU Mk1 Mainboard PCB
  • Backplate PCB (with screws and nuts for mounting)
  • Electronic Components Kit
  • USB Mini Cable (for power only)
  • Operator's Technical Manual (downloadable .pdf - English language only)

The kit is supplied with our 'Operator's Technical Manual' (as a downloadable .pdf - English language only) which describes in detail what the arithmetic unit is and how ALUs are used more generally in computational architecture. The manual also explains how to fully construct and operate the S1-AU Mk1 and gives a primer on binary operations (addition, subtraction & twos complement) for those who may not be familiar with binary arithmetic. Our mainboard PCB has been carefully crafted to complement the manual and aid construction.

The S1-AU Mk1 is recommended for ages 16+. Some soldering experience is required to construct the kit.

The ARITH-MATIC S1-AU Mk1 performing 4-bit accumulation

RRP: £49.95 (ex delivery).
Get 10% off* with code OCT10

Shipping to UK / EU / US only.
Shipping & Returns Policy

*Offer lasts until 31st October. Excludes shipping.

Spare Parts and Volume Purchases

We can supply a range of spare parts kits for the S1-AU Mk1, from individual components through to replacements packs. For more information and prices please email:

If you are interested in purchasing ARITH-MATIC products in larger quantities, you may be entitled to discounts. Please email for a no-fuss quotation.