Once upon a time, for those who cracked open the pages of IEEE Spectrum you may 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 related potentiometers and op-amps to arrange representations of knotty differential equations and browse the options as various output voltages. But then digital computer systems conquered all, making analog computing as out of date as radio coherers, mechanical televisions, and punched playing cards. Almost.
Like different written-off applied sciences which have seen comebacks comparable to vinyl data, Nixie tubes, and airships, analog computer systems have their adherents striving for a revival. In 2017, Yannis Tsividis wrote a characteristic article for Spectrum describing his analysis at Columbia University into the prospects of digital-analog hybrid pc chips. The digital component provides ease of use, whereas the analog component gives energy-efficient options to many real-world varieties of issues.
When the article was revealed, I assumed it made some compelling factors, however as an informal experimenter I didn’t actually have a great on-ramp to analog computing. That modified final 12 months once I noticed that startup Anabrid was providing a brand-new analog machine, the US $513 THAT.
Anabrid’s primary gig is creating hybrid analog-digital chips of the type pioneered by Tsividis.
It’s THAT is meant to lift consciousness of the chances of recent analog computing. THAT is an acronym for The Analog Thing, 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. But the THAT is not only a cut-down toy. Multiple THATs may 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, comparable 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
Like the analog computer systems that after graced the ads in Spectrum, the THAT is programmed by wiring up components that carry out mathematical features with quick patch cables. You want to supply your individual solution to show the THAT’s output voltages—for me it felt solely applicable to hook up an previous 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. As it’s been a minute since I final took down Erwin Kreyszig’s Advanced Engineering Mathematics 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. Soon 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 previous analog oscilloscope I’d cadged from my older brother.
But I wished to check out the hybrid strategy. The pure selection was to construct on Anabrid’s demo patch for a lunar-lander recreation: beginning above the floor with a restricted quantity of gasoline, 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 gasoline runs out.
With an oscilloscope, the sport lacks a sure visible élan, with the gasoline and altitude readings displayed as two horizontal traces. And a essential component of any lunar-lander recreation can also be lacking—figuring out whether or not or not the spacecraft’s pace in the meanwhile of touchdown ends in a swish landing or a contemporary crater. But these deficiencies may very well be addressed digitally.
On the left are the differential equations that mannequin the flight of the lunar lander of their textbook type. On the proper is how they’re encoded into the weather supplied by the THAT, comparable 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 defend. The LCD show makes use of almost all of the pins on a daily Arduino Uno, however two analog inputs remained out there to learn the voltages representing altitude and gasoline.
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 gasoline degree find yourself approximated as numbers between 0 and 675. But 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 defend and a ribbon cable operating to the THAT’s hybrid port. It is feasible to exert some energetic management of the THAT through the hybrid port, for instance, commanding it to reset to its preliminary circumstances and fixing an equation. However, with solely two analog inputs out there after accommodating the LCD defend, 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 fashion. Fuel is displayed as a dwindling horizontal bar. Speed is computed and displayed by sampling the spacecraft’s altitude about 10 instances 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 informed in the event that they landed safely, broken their spacecraft, or have been destroyed on impression. The program then waits till the THAT is reset for an additional try.
Somewhat 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 talent with the throttle. As an intro to a type of computing now alien to just about all engineers, the THAT is about as effectively designed an on-ramp as you may want for. Now it’s time to take down Kreyszig and begin exploring my very own physics fashions!
This article seems within the January 2024 print difficulty as “A Brand New Analog Computer.”