Analogue to Digital

There are two kinds of electronic signals: analogue and digital. An electronic signal is used to receive or send information between devices. How has this technology been used over time? Find out below...

By The National Museum of Computing

Image courtesy of Bedford Aeronautical Heritage Group (BAHG).

Analogue Signal Graph (2020) by The National Museum of ComputingThe National Museum of Computing

Voltage against time: Analogue signal

An analogue signal is a continuous current. When demonstrated on a graph, with the voltage value plotted against time passed, an analogue signal is smooth, uniform and continuous. 

Digital Signal Graph (2020) by The National Museum of ComputingThe National Museum of Computing

Voltage against time: Digital signal

In contrast, a digital signal is broken up into separate chunks. Thus, when demonstrated on a graph, a digital signal appears as jagged square waves or ‘steps’, which result from approximated rather than precise values. 

How do these signals relate to the real world?

The real world closely mirrors the analogue world; humans use their senses to process analogue information in a continuous stream with infinite possibilities. The digital realm is defined by a finite number of possibilities; it is a numerical representation of the real world.

Analogue to Digital Pictogram (2020) by The National Museum of ComputingThe National Museum of Computing

A practical example

A digital value can be represented as a number of items, for example: three pears. When the pears are weighed on a set of scales, the force produced is a continuous output value which is the analogue representation of the three pears. 

Solartron Minispace (1958) by SolartronThe National Museum of Computing

Analogue computers

In the early 20th century, many manufacturers were developing analogue computers to execute mathematical calculations. They used circuitry based on amplifiers which were capable of transforming a weak input signal into a much stronger output signal. 

Mechanical Calculator (20th Century) by The Muldivo Calcultaing Machine Co. Ltd.The National Museum of Computing

Examples of early non-electronic analogue computers

The earliest analogue computers were built for specific tasks, such as predicting tides. A key characteristic of analogue computers is they are used to simulate real world actions as mathematical problems; analogue computing actually predates electronic circuits.

Antikythera Mechanism (Ancient Greek civilisation, exact date unknown.) by Ancient Greek scientistsThe National Museum of Computing

Antikythera Mechanism - Ancient Greece (60/205 BC)

The Antikythera Mechanism has been described as the world’s first analogue computer. The device is thought to be a mechanical model of the solar system which was used to predict motions of planets, moons and other astronomical phenomena. 

Slide Rule (Circa 1620) by William OughtredThe National Museum of Computing

Slide rule - 17th century

The slide rule was an analogue device used for logarithmic calculations, multiplication and division. Although only accurate to two decimal places, it was essential to the work of scientists, engineers and mathematicians for several decades.    

Planimeter (1814) by Johann Martin HermannThe National Museum of Computing

Planimeter - Early 19th century

A planimeter can measure the area of a 2D shape. A mechanical planimeter is an example of a simple differential analyser - an analogue computer capable solving differential equations using mathematical integration, performed by wheel-and-disc mechanisms. 

Meccano Differential Analyser - Dr Maurice Wilkes (Right) (1934) by Manchester UniversityThe National Museum of Computing

Meccano Differential Analyser - 20th century

Differential analysers were one of the first advanced computing devices used operationally. The Meccano differential analyser, built at Manchester University in 1934, was actually constructed using Meccano parts taken from a 19th century children’s model construction kit. 

EDSAC (Electronic Delay Storage Automatic Calculator) (1949) by Sir Maurice WilkesThe National Museum of Computing

Where did this innovation lead?

The Meccano Differential Analyser was also used at Cambridge University, at one point supervised by Maurice Wilkes. Wilkes went on to invent EDSAC, the world’s first practical general purpose stored program electronic computer, an operational replica of which is housed at TNMOC.

Comet 3B (XP915) Aircraft (1968/1977) by Bedford Aeronautical Heritage Group (BAHG)The National Museum of Computing

Electronic analogue computers

Analogue computers are ideally suited to problems that can be solved using equations. Applications dealt with by analogue computers include: planetary, satellite orbits, nuclear weapons, navigation and guidance systems (for ships and aircraft) and pilot simulators.     

Solartron Minispace (1958) by SolartronThe National Museum of Computing

The Solartron Minispace Computer (1958)

The Solartron Minispace is an electronic analogue calculator which uses ten amplifiers in a circuit to complete mathematical processes. These calculations were used to understand and simulate physical systems, for example, aerodynamics in a guided weapon control system. 

PACE TR48 Installed on the Comet 3B (XP915) Aircraft (1968/1977) by Bedford Aeronautical Heritage Group (BAHG)The National Museum of Computing

The PACE TR48 Computer (1961)

The PACE TR48, a solid-state transistorised analogue computer, was built by Electronics Associates Incorporated (EAI). Despite an impressive capability to solve most engineering problems, the TR48 was still compact enough to sit on a laboratory desk.   

BA 1-11 (XX105) Aircraft in Flight (1972/1977) by Bedford Aeronautical Heritage Group (BAHG)The National Museum of Computing

Application at the Royal Aircraft Establishment (RAE)

Between 1968 and 1977, PACE TR48 computers were used to aid research into the first automatic approach and landing systems for aircraft at the RAE (Bedford). A modified version of a TR48 was installed on a Comet 3B (XP915) aircraft by the Blind Landing Experimental Unit (BLEU). 

Laboratory at the Royal Aircraft Establishment (RAE) Bedford (1968/1977) by Bedford Aeronautical Heritage Group (BAHG)The National Museum of Computing

In the laboratory

Two PACE TR48 computers were located at the RAE laboratory. During research, one TR48 would be programmed with a new aircraft control system design, whilst the second would simulate conditions such as aircraft aerodynamics and atmospheric disturbances. 

Scientists Operating the PACE TR48 Onboard the Comet 3B (XP915) Aircraft (1968/1977) by Bedford Aeronautical Heritage Group (BAHG)The National Museum of Computing

Onboard the aircraft

Having passed laboratory tests, new programs would undergo a real-world test flight using the modified PACE TR48 on the Comet 3B aircraft. The TR48 could automatically operate elements of the flight control system; it became known as the ‘versatile autopilot.’ 

PACE TR48 Installed on the BAC 1-11 (XX105) Aircraft (1972/1977) by Bedford Aeronautical Heritage Group (BAHG)The National Museum of Computing

In the 'Flying Laboratory'

In 1972, the modified PACE TR48 was transferred from the Comet 3B to the BAC 1-11 (XX105) aircraft, which had recently been acquired by the BLEU and was essentially kitted out as a ‘flying laboratory’.  

PACE TR48 Analogue Computer (1961) by Electronics Associates Incorporated (EAI)The National Museum of Computing

At The National Museum of Computing (TNMOC)

At TNMOC, visitors can see a PACE TR48 programmed to simulate a car suspension system travelling over a bump. TNMOC boasts several volunteers who used the TR48 in their computing careers. One, a rocket scientist, used the TR48 to run a simulation model for rocket trajectories. 

EAI 180 Analogue Computer (1972) by Electronics Associates Incorporated (EAI)The National Museum of Computing

The EAI 180 Computer (1972)

The EAI 180 analogue computer combines mechanical and electrical components to simulate reasonably complex  problems. Adaptable, compact and affordable, they were used by students at Sydney University to mathematically model and solve engineering problems.       

Amstrad Mega PC (1993) by AmstradThe National Museum of Computing

Digital computers

Analogue and digital signals can be understood as two different languages; some electronic devices are able to ‘speak’ both languages, while others can only communicate in one. Digital computers are not capable of processing analogue data in the same way that humans can.   

Binary Counter (2021) by The National Museum of ComputingThe National Museum of Computing

Digital signals and binary code

Any data that a modern computer needs to process must be converted into a digital signal made up of binary digits. Binary is a number system used by computers that has just two possible values, 1 and 0. These binary digits, called ‘bits’, are used to store data. 

Binary Counter Demonstration (2021) by The National Museum of ComputingThe National Museum of Computing

Demonstration of counting using binary numbers

GEC Electronic Tube (Thermionic Valve/Vacuum Tube) (First introduced in 1956) by General Electric Company (GEC)The National Museum of Computing

Computer processing using electronic switches

Simply, a computer processor is a collection of switches in an ‘on’ or ‘off’ position, represented by the binary digits 1 or 0.  A computer processes data by turning the switches on or off in sequence. A valve (pictured) is an example of an electronic switch.     

Colossus Rebuild (2008) by Tony SaleThe National Museum of Computing

The first entirely digital semi-programmable computer

A computer processes information using devices such as valves, relays or transistors; a valve or a transistor is an electronic switch and amplifier. The revolutionary WWII codebreaking machine Colossus, the first all-digital semi-programmable computer, has over 2,500 valves. 

PACE TR48 Analogue Computer (1961) by Electronics Associates Incorporated (EAI)The National Museum of Computing

Analogue circuits

Most of the essential components that make up an electronic circuit are analogue. Typically, analogue circuits are a complex combination of components, which makes them more challenging to design compared to the equivalent digital application. 

Raspberry Pi 3 Computer (2016) by Raspberry PiThe National Museum of Computing

Digital circuits

Easier to design than their analogue counterparts, digital circuits are more expensive to build; ordinarily consisting of logic gates, transistors and microchips. Generally, a digital signal will use two values, one high voltage and one low voltage; a binary form of signalling. 

Mini-ITX Printed Circuit Board/Motherboard (2000s) by IntelThe National Museum of Computing

Modern day information processing

Today, computer processors use billions of transistors etched onto a silicon chip, which are activated when they receive an electronic signal. It is not unusual to have a circuit that uses both analogue and digital components, operated using an analogue to digital converter.   

Credits: Story

With thanks to Bedford Aeronautical Heritage Group (BAHG) who so kindly provided information and photographs concerning the application of the PACE TR48 analogue computer at the Royal Aircraft Establishment (RAE), Bedford. 

Credits: All media
The story featured may in some cases have been created by an independent third party and may not always represent the views of the institutions, listed below, who have supplied the content.
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