As soon as upon a time, when you cracked open the pages of IEEE Spectrum you can spot full-page ads for analog computer systems, boasting of their ease of use and even—within the case of 1 mannequin constructed right into a cart with wheels—their portability. Engineers linked potentiometers and op-amps to arrange representations of knotty differential equations and browse the options as various output voltages. However then digital computer systems conquered all, making analog computing as out of date as radio coherers, mechanical televisions, and punched playing cards. Nearly.
Like different written-off applied sciences which have seen comebacks similar to vinyl data, Nixie tubes, and airships, analog computer systems have their adherents striving for a revival. In 2017, Yannis Tsividis wrote a function article for Spectrum describing his analysis at Columbia College into the potentialities of digital-analog hybrid pc chips. The digital factor gives ease of use, whereas the analog factor supplies energy-efficient options to many real-world sorts of issues.
When the article was printed, I believed it made some compelling factors, however as an off-the-cuff experimenter I didn’t actually have a superb on-ramp to analog computing. That modified final 12 months after I noticed that startup Anabrid was providing a brand-new analog machine, the US $513 THAT.
Anabrid’s fundamental gig is creating hybrid analog-digital chips of the kind pioneered by Tsividis.
It’s THAT is meant to lift consciousness of the probabilities of contemporary analog computing. THAT is an acronym for The Analog Factor, and it’s a small open-source machine composed largely of discrete op-amp built-in circuits.
The THAT is smaller than the industrial-grade machines of yore, with simply eight potentiometers for setting parameters and 5 integrators, together with a set of supporting summers, inverters, comparators and so forth. However the THAT isn’t just a cut-down toy. A number of THATs might be chained collectively if extra processing energy is required, and a hybrid connection port is supplied to make it simpler to interface a THAT with a digital pc.
The THAT analog pc [left] has sockets for connecting varied parts, similar to integrators, that correspond to mathematical operations. I displayed its outputs utilizing an LCD display screen [top right], protoboard interface [middle right] and Arduino Uno [bottom right].James Provost
Just like the analog computer systems that when graced the ads in Spectrum, the THAT is programmed by wiring up components that carry out mathematical features with brief patch cables. You could present your individual approach to show the THAT’s output voltages—for me it felt solely applicable to hook up an outdated analog oscilloscope that I’d cadged from my older brother a while in the past on normal rules.
It was time to strive some computing. Because it’s been a minute since I final took down Erwin Kreyszig’s Superior Engineering Arithmetic to ponder differential equations, I used to be glad to see that the THAT’s accompanying guide is chock-full of examples and patch diagrams. Quickly I used to be watching Euler spirals and simulations of neural spiking bloom into phosphorescent life, observing their evolution as I twisted potentiometers to regulate parameters.
It felt solely applicable to hook up an outdated analog oscilloscope I’d cadged from my older brother.
However I needed to check out the hybrid strategy. The pure selection was to construct on Anabrid’s demo patch for a lunar-lander sport: beginning above the floor with a restricted quantity of gas, a spacecraft is in grip of the moon’s gravity. The participant should management the spacecraft’s engine throttle by turning a potentiometer in order that the spacecraft lands earlier than the gas runs out.
With an oscilloscope, the sport lacks a sure visible élan, with the gas and altitude readings displayed as two horizontal strains. And a vital factor of any lunar-lander sport can also be lacking—figuring out whether or not or not the spacecraft’s pace in the meanwhile of touchdown leads to a sleek landing or a recent crater. However these deficiencies could possibly be addressed digitally.
On the left are the differential equations that mannequin the flight of the lunar lander of their textbook kind. On the fitting is how they’re encoded into the weather supplied by the THAT, similar to integrators and comparators. The numbers inside circles seek advice from the potentiometers used to set the values of parameters.James Provost
For my digital pc and graphics show, I dug out an Arduino Uno and a small LCD touchscreen protect. The LCD show makes use of practically all of the pins on a daily Arduino Uno, however two analog inputs remained accessible to learn the voltages representing altitude and gas.
This did entail sacrificing some precision. Internally, the THAT represents portions utilizing a spread between -10 and +10 volts. That full vary would curdle the analog-to-digital convertors constructed into most microcontroller boards, so the THAT compresses and shifts that vary for the hybrid port. There, voltages range between 0 V and three.3 V. The Arduino Uno operates at 5 V, and reads with 10-bit precision, so the altitude and gas stage find yourself approximated as numbers between 0 and 675. However that’s tolerable, on condition that my LCD has solely 320 vertical pixels at most to show the spacecraft’s location above the floor.
I made up an Arduino protoboard with connectors for the LCD protect and a ribbon cable working to the THAT’s hybrid port. It’s doable to exert some lively management of the THAT by way of the hybrid port, for instance, commanding it to reset to its preliminary situations and fixing an equation. Nevertheless, with solely two analog inputs accessible after accommodating the LCD protect, I used to be utilizing the Arduino as a purely passive show.
I wrote a program to show the lunar floor and the participant’s spacecraft in traditional vector-like model. Gasoline is displayed as a dwindling horizontal bar. Pace is computed and displayed by sampling the spacecraft’s altitude about 10 occasions per second and dividing the change in altitude by the point interval between measurements. When the altitude reaches zero, the pace is checked and the participant is advised in the event that they landed safely, broken their spacecraft, or have been destroyed on influence. This system then waits till the THAT is reset for one more try.
Considerably to my shock, my hybrid contraption labored easily. Spacecraft rose and fell on the show in accordance with the legal guidelines of physics encoded within the THAT’s nest of wiring, and lived or died relying on my ability with the throttle. As an intro to a type of computing now alien to almost all engineers, the THAT is about as nicely designed an on-ramp as you can want for. Now it’s time to take down Kreyszig and begin exploring my very own physics fashions!
This text seems within the January 2024 print concern as “A Model New Analog Pc.”