Electronic engineers (like what I am) tend to partition the world into two views: analog and digital. Analog systems represent information as continuous signals that can take on any value within a range. For example, think of a dimmer switch for a light or the smooth sweep of a needle on a gauge. These systems mimic the real world, where quantities like sound, temperature, or voltage change smoothly over time.

Digital systems, by contrast, represent information using discrete steps or values, which are typically represented in binary form as 0s and 1s. Instead of a smooth curve, you get a staircase of distinct levels. For example, think of a light switch that’s either on or off, or a digital clock that jumps from 12:00 to 12:01.

These days, we are surrounded by digital systems to such an extent that even young adults may struggle to tell the time using an analog clock. (And don’t even get me started about that famous YouTube video showing two 17-year-olds trying to use a rotary dial telephone.)

On a related note, when most people hear the term “calculator,” they tend to think of an electronic digital implementation. However, long before electronic calculators arrived on the scene, engineers predominantly used mechanical analog calculators known as slide rules.

Similarly, when most people hear the term “computer,” they tend to think of electronic digital implementations, such as microprocessor-based tablets, notepads, laptops, towers, and servers. Things weren’t always this way. As usual, the ancients (by which I mean anyone older than me) had more than a few tricks up their sleeves (or hidden in the folds of their robes).

For example, the term “perpetual calendar” refers to a calendar that’s valid for many years (as opposed to one that is discarded at the end of the current year). These are typically designed to determine the day of the week for a given date in the past or future. It’s challenging enough to devise a program that can accomplish this using a digital computer. So, it’s amazing to me that circa 1831–1835, the Italian astronomer and mathematician Giovanni Plana managed to devise a mechanical analog computer out of pulleys and cylinders that could implement a perpetual calendar. This little scamp (the computer, not Giovanni) could calculate the day of the week for any given date from 1 to 4000 AD (CE), while accounting for leap years and the irregularities of the Gregorian and Julian calendars.

How about the fact that Sir William Thomson (Lord Kelvin) created a mechanical analog computer in 1872 that could be used to predict the tides? This little rascal (the computer, not William) used a system of pulleys and wires to automatically calculate predicted tide levels for a set period at a particular location. Your knee-jerk reaction might be “How hard can this be — don’t tides simply rise and fall twice a day because of the Moon’s gravity?” I’m glad you asked. The short answer is “No.” The longer answer is that there are multiple influences that need to be accounted for and considered simultaneously. Gravity is just one of these, and even that’s not simple. The relative positions of the Earth, Moon, and Sun constantly change, and their influences combine through many overlapping cycles with different periods (diurnal, semi-diurnal, fortnightly, monthly, annual, and longer).

You can see an example of how William’s wonderful widget worked in this brilliant Veritasium video on YouTube. This offering also showcases a marvelous mechanical mechanism that can perform integration in such a cunning way that it brings a tear of joy to my eye.

Are you familiar with the Discworld novels by Terry Pratchett? These are set on a flat, circular world balanced on the backs of four giant elephants, which themselves stand on the shell of Great A’Tuin, a colossal spacefaring turtle slowly swimming through the cosmos. Within this setting, Pratchett explores every aspect of life — magic, politics, religion, science, and human nature — through biting satire coupled with warm humor. The stories parody our own world while developing their own rich mythology, cultures, and history.

In Making Money, one of the characters builds a mechanism to model the circulation of money. This creation is something that we would recognize as a fluidic (water-based) analog computer. When I first read this, I thought it was a splendidly silly idea. It was much later that I discovered Terry had based this machine on the round-world (i.e., real-world) MONIAC (Monetary National Income Analogue Computer), which was created in 1949 by the New Zealand economist Bill Phillips.

The reason I mention all this is that I graduated from high school and entered Sheffield Polytechnic (now Sheffield Hallam University) in England in the summer of 1975. At that time, the only computer in the Engineering Department’s building was a massive analog machine similar to the one shown below. (We did have access to a digital mainframe; however, that was located in a separate building. We created programs for that machine in FORTRAN on decks of punched cards, but that’s a story for another day.)

Analog computing machine at the Lewis Flight Propulsion Laboratory circa 1949 (📷: Wikipedia/NASA)

These analog computers consisted of numerous independent modules, including amplifiers, adders, subtractors, integrators, differentiators, comparators, and other components. The inputs and outputs of these modules were connected using patch cords to configure specific computational setups, which could be used to perform different calculations and simulations.

Although many people today tend to “turn up their noses” at the thought of analog computers, they were a fantastic solution in their time. It’s essential to recall that analog techniques were well understood at that time, whereas digital methods were still a mystery to most engineers.

Furthermore, performing any meaningful digital signal processing (DSP) typically requires a substantial number of digital components, and these were costly at the time. By contrast, remarkably sophisticated analog processing can be achieved with just a handful of analog components.

I just ran across a photo of the Heathkit EC-1 (see below). This was a truly iconic machine in the history of educational computing. It was one of the earliest analog computers designed for teaching and demonstration purposes. The EC-1 was based on operational amplifiers (op-amps) implemented using vacuum tubes (see also Vunderful Vacuum Tubes). It offered hobbyists and students in the late 1950s and early 1960s a hands-on way to understand how continuous systems could be modeled and solved electronically.

Heathkit EC-1 educational analog computer (📷: Wikipedia/Michael Holley)

As usual, writing this column has reminded me how much fun I had working with analog computers when I wore a younger man’s clothes. In turn, this reminded me of THE ANALOG THING (THAT), which is, as they say on their website, “[…] a modern, high-quality, low-cost, open-source, and not-for-profit cutting-edge analog computer.” I have to say that I would love to play with one of these little beauties. Sad to relate, funds are short, but one day...

But wait, there’s more! At the same time that analog computers were being introduced into classrooms and laboratories during the late 1950s and early 1960s, a parallel revolution was unfolding in music studios. Engineers realized that the same voltage-controlled amplifiers, filters, and oscillators used in analog computation could also be employed to generate and sculpt sound, thereby leading to the development of the analog synthesizer.

These devices generate audio signals directly as electrical waveforms. Such signals — typically in the audio frequency range (20 Hz to 20 kHz) — are shaped by voltage-controlled circuits to form musical tones. In this case, the main building blocks are Voltage-Controlled Oscillators (VCOs) that generate raw waveforms (sine, triangle, sawtooth, square, pulse…), Voltage-Controlled Filters (VCFs) that shape the harmonic content of the sound by cutting or emphasizing frequencies, Envelope Generators (EGs) that produce time-varying control voltages that describe how sounds evolve in terms of Attack, Decay, Sustain, and Release (ADSR), Low-Frequency Oscillators (LFOs) that generate slow periodic modulation signals (below ~20 Hz) used for vibrato, tremolo, filter sweeps, etc., and Voltage-Controlled Amplifiers (VCAs) that dynamically control the loudness (i.e., shape the amplitude) of the sound using control signals (e.g., from an envelope generator).

All I know is that, if money were no object, then I would soon be found drooling over a Moog One 16‑Voice Polyphonic Analog Synthesizer. Sad to relate, I won’t be investing in one of these bodacious beauties anytime soon, but at least I can dream about it.

How about you? Have you had any experiences with analog computers or synthesizers that you’d care to share with the rest of us? As always, I welcome your captivating comments, querulous questions, and sagacious suggestions, all of which you can share on Hackster’s Throwback ThursdaysDiscord channel. I look forward to seeing you there.

P.S. Don’t forget that you are only a click away from perusing and pondering all of my Throwback Thursdayscolumns in one place.

P.P.S. Please feel free to email me at max@clivemaxfield.com if you have any questions about this column or if you have any requests or suggestions for future articles.

Clive “Max” Maxfield

I began my career as a designer of CPUs for mainframe computers. Now I’m a freelance technical consultant and writer.