Analog computer, past present and future.  - Page 1
Forum section: electronics / general

author: munorc
author_rank: Regular Contributor
timestamp: March 07, 2025, 05:09:30 pm
content: There is another topic alongside this regarding Analog electronics in general. I thought I would start this specific to analog computers.I have been in the computer realm for most of my life, supporting fairly large scale HPC installations. My engineering career started just at the twilight of analog computing, and I started in the realm of punch cards and FORTRAN on big mainframes in the early 80'sI recall the room sized analog computers that we had in the engineering departments. They were mostly mothballed and waiting to be hauled out.I started off as a lab support scientist at the University where I still work. We had a couple of Analog computers shoved in the corner. These were student training units, small scale desktop type units. A Vacuum tube based Donner 3500 and a solid state EAI 180. I have kept these, along with many other examples of old engineering tools, in my office for 30 years now. I had also kept a PC board assembly since it had some old 12AX7 tubes on it. One day I decided to figure out what it was and determined it is a Philbrick GAP/R tube based operational amplifier dating back to the late 50's. That raised my interest in these old analog computers I have kept all these years.The Donner 3500 has a compliment of five dual chopper stabilized amplifiers. Each amplifier can serve as a summer and an integrator giving 5/10 summer channels or 5 summer+integrator. The main difference is the circuitry to present the initial condition and operational control.I brough the unit up with all the amplifiers removed to verify the power supply. It has a +420V/-310V power supply, alongside the 6.3V filament supply. In contrast, the Philbirck GAP/R board needs stabilized +/-300V supply. Everything check out so I started testing the amplifier channels. Overall they are functional.Both of these designs have a working voltage of +/-100V and have an open loop gain of 10^7, pretty impressive for a vacuum tube design from the 50's.The EAI 180 has a working voltage of +/-10V.Now that these have caught my attention, it is interesting to see how much interest there is in preserving these. There are also entities that are developing new implementations and working on ways of integrating them in to the modern HPC computing world.

author: TimFox
author_rank: Super Contributor
timestamp: March 07, 2025, 05:14:13 pm
content: Does the GAP/R need +/- 600 V?I thought it was 300 V, which should be enough to get +/- 100 V output.That EAI unit is beautiful!

author: schmitt trigger
author_rank: Super Contributor
timestamp: March 07, 2025, 05:17:13 pm
content: I believe that it is very safe to say that there will be significant interest in these devices, specifically because they look so well preserved.Keep them!OTOH, If you can’t afford to keep them, there are several computer museums which I believe would gladly take them.

author: schmitt trigger
author_rank: Super Contributor
timestamp: March 07, 2025, 05:19:12 pm
content: Difficult to see from the picture, but does the EAI unit have a digital display??

author: TimFox
author_rank: Super Contributor
timestamp: March 07, 2025, 05:34:27 pm
content: I have posted this previously.Before retirement, I visited a Boeing facility numerous times, and often read their monthly newsletter to look at historical photos of cool aircraft. One month, they had a photo, ca. 1950, of an engineer (white shirt and tie) seated between a tall 19 inch rack cabinet (analog computer) and a blackboard (identifying equation terms with computer pots). The caption read “the computer generated so much heat that 400 vacuum tubes were required to remove it”. Next month’s issue had letters from employees older than that writer.

author: munorc
author_rank: Regular Contributor
timestamp: March 07, 2025, 05:42:10 pm
content: Quote from: schmitt trigger on March 07, 2025, 05:17:13 pmYou are correct. I corrected it above.

author: munorc
author_rank: Regular Contributor
timestamp: March 07, 2025, 05:44:44 pm
content: Quote from: TimFox on March 07, 2025, 05:34:27 pmInteresting, I now run computers that are 75kW per rack, and are water cooled.

author: munorc
author_rank: Regular Contributor
timestamp: March 07, 2025, 05:46:34 pm
content: Quote from: schmitt trigger on March 07, 2025, 05:19:12 pmThis model was the basis of their hybrid computer. The lower portion would be the digital section, which this unit lacks.The readout is a DMM.

author: munorc
author_rank: Regular Contributor
timestamp: March 07, 2025, 05:50:58 pm
content: Here is the GAP/R USA-3 Universal Stabilized Amplifier.Like the Donner amplifier boards, it uses an electromechanical chopper (Airpax A-175) to stabilize.

author: munorc
author_rank: Regular Contributor
timestamp: March 07, 2025, 05:52:36 pm
content: Here is the Donner 3013 dual channel stabilized amplifier.They are plug in boards, with the base unit having a backplane of "blue ribbon" edge connectors.

author: coppercone2
author_rank: Super Contributor
timestamp: March 07, 2025, 05:56:41 pm
content: how good would a analog computer need to be to get close to a modern PC at solving somerthing?Like analog computer parts with 32 bit resolution with 2 ohm impedance running at ghz, run in the coldhttps://ieeexplore.ieee.org/document/9199260

author: munorc
author_rank: Regular Contributor
timestamp: March 07, 2025, 06:09:08 pm
content: The entire solution paradigm differs. Analog computers are inherently parallel and operate in the continuous versus discrete realm.As complexity increases in the problem size, that requires an increase in the number of functional components, e.g. summers, integrators, multipliers. The solution time is not affected.Anabrid is currently producing highly integrated analog computer designs that implement all patching dynamically. The intent is to marry them to HPC deployments, letting the portion of the problem that is better solved in the analog realm assigned to that portion. This similar to how quantum computing qbits are currently utilized.

author: coppercone2
author_rank: Super Contributor
timestamp: March 07, 2025, 06:10:20 pm
content: But for accuracy right now a digital computer far outpassses a analog one. what would it take to make the analog one like similar?

author: munorc
author_rank: Regular Contributor
timestamp: March 07, 2025, 06:18:13 pm
content: The accuracy is highly dependent on the accuracy of the components. In the heyday, precision models had thermally stabilized components, and much higher tolerance on parts.In the digital realm, it is dependent on the number of bits. GPU's were fast, but they were only 16 and 32 bit. Now they have evolved moved to 64 bit floating point on modern GPUS'sIt is a similar hybrid world. We run GPU's in our HPC systems, but some problems run better on the CPU, some do very well on a GPU. This is for engineering type problems where we need 64 bit floating point.

author: TimFox
author_rank: Super Contributor
timestamp: March 07, 2025, 06:26:35 pm
content: The old rule of thumb was that analog computers were slow to program, but returned a result “immediately”.Since they often output to a mechanical pen recorder, they often were set up to run in real time at a rate much slower than the process being calculated.When Shure Bros. introduced their V15-II phono cartridges in 1966, they advertised them as “computer designed”. They meant that they had simulated the response of the resonant electromechanical system with an analog computer, optimizing the tuning to get a desired response by tweaking the parameters.

author: munorc
author_rank: Regular Contributor
timestamp: March 07, 2025, 06:52:55 pm
content: Analog computer modeling always required scaling. Amplitude has to be scaled in to the machine unit range, e.g. +/-100V, +/-10V. Same goes for time scaling. It needs to fit in to what is observable. This could mean compression or expansion of time scale, depending on what is being modeled. As you mention, if using a pen recorder, it needs to be slow enough to not exceed the mechanical constraints, e.g. accelerating the mass of the pen. If we want to observe on an oscilloscope, then it is desirable to have shorter time span and run in repeat mode to get observable traces. This can be modified by changing the feedback parameters of the capacitors and resistors employed in the compute elements.With modern hybrid approaches, we can use a digital interface to "patch" the problem through a crossbar, and capture the output through a ADC. Time scale is not as relevant.

author: Kleinstein
author_rank: Super Contributor
timestamp: March 07, 2025, 07:09:43 pm
content: Quote from: coppercone2 on March 07, 2025, 06:10:20 pmThe accuracy for analog computing is limited. Already 16 bit needs quite some effort (e.g. high end audio). The extra effort goes up a lot for very high accuracy. There is essentially no way for an analog computer to reach 32 bit resolution. For some problems intermediate results may need much higher resolution than the final result - so it is not that easy to tell how much accuracy is actually needed. A few problems are especially bad and may be ill posed problems. Some parts just have limitations not just in the accucy of the computer, but also the starting values to enter.To a certain degree quantum computers can be similar to analog computers. However there are extra aspects that allow some kind of error correction and this way overcomming the noise problems, though at the cost of needing significant extra Qbits and maybe reduced speed.

author: NE666
author_rank: Frequent Contributor
timestamp: March 07, 2025, 07:12:38 pm
content: As fascinating as these devices are, I really can't see analog 'computing' making a significant return.If we're talking about the capacity for massively parallel operations and low latency calculations, that's been addressed very successfully in the digital domain in the past decades. What we already have is keeping pace with our aerospace, manufacturing, construction and communication ambitions, and is driving forward AI/ML, scientific discovery and the 'technologies of tomorrow' at a sometimes alarming rate. Apart from wanting to read our neighbor's encrypted messages, Mr Moore's law hasn't really stymied us yet.What do analog techniques offer us today, that isn't really just an interesting niche solution in search of a problem? Companies in this area, on the surface, all seem to be early stage startups with no clear statements of the 'USP' i.e. *what* are the problem sets that it would make sense to invest in analog solutions for, rather than existing digital or ASIC ones? And what's the cost benefit, given the millions of person-hours of experience and re-usable assets invested in the latter?

author: TimFox
author_rank: Super Contributor
timestamp: March 07, 2025, 07:25:41 pm
content: Quote from: munorc on March 07, 2025, 06:52:55 pmWith appropriate time scaling, using an analog computer with CRO readout, for a task analogous to the Shure phono cartridge design, can be similar to adjusting an RF filter using a swept-frequency spectrum analyzer. Of course, it’s hard to compete with brute-force digital computation on modern machines. In 1966, Shure’s task would’ve required Hollerith cards.

author: Analog Kid
author_rank: Super Contributor
timestamp: March 07, 2025, 08:21:22 pm
content: Pardon my coming late to the party with an observation that may or may not be relevant:Would it be accurate to characterize analog computers as more like a slide rule compared to the digital computer's digital calculator?And as a more general question, what would you say are the possible applications of analog computing going forward? what would it be good at? what could it accomplish as a supplement to digital computing?BTW, I love that this discussion is taking place. (Well, given my "handle" ...)

author: tggzzz
author_rank: Super Contributor
timestamp: March 07, 2025, 08:22:44 pm
content: Quote from: TimFox on March 07, 2025, 07:25:41 pmI first saw a bookcase sized analogue computer solving differential equations during a maths class trip to a local university, c1973. The analogue computer had clear attractions compared with the alternatives, but my maths teacher had a strong suspicion that digital would win in this application.She was right.Analogue computing has a future under a limited number of circumstances, lower power and/or lower latency being the principal requirements.

author: tggzzz
author_rank: Super Contributor
timestamp: March 07, 2025, 08:29:14 pm
content: Quote from: Analog Kid on March 07, 2025, 08:21:22 pmNo. Slide rules don't solve differential equations.QuoteNot much, unless the system power is lower or frequency higher.Analogue processing OTOH, it still under appreciated.

author: coppercone2
author_rank: Super Contributor
timestamp: March 07, 2025, 09:29:55 pm
content: Quote from: Kleinstein on March 07, 2025, 07:09:43 pmThere must be a way, but its probably obscene. Everything would need to run in low impedance to keep down the noise? Opamps with miliohm dividers and such? 5000 amp super conductive power rails? Placed some where in between solar systems?I often wondered if they noticed any 'quirks' in the voyager telemetry reduce when it got further from us. Like less noise because of solar activity and things like that, or glitches that went away. Like muon radiation and things like that.I imagine if you setup some equipment on the moon, like a spectrum analyzer, you might see some of those spurs go away... could lose the 60hz notch filter maybe?I guess most of the noise would be intrinsic to the parts @ their bias levels, but its still interesting to think about.

author: brucehoult
author_rank: Super Contributor
timestamp: March 07, 2025, 10:24:46 pm
content: Quote from: Kleinstein on March 07, 2025, 07:09:43 pmIt seems quite unlikely to me that any analogue system of any complexity, including hi fi audio, actually has accuracy comparable to a 16 bit linear digital system. Maybe it's possible to detect that size of incremental change, especially near to 0, but at the limits? And with perfect linearity? And with what frequency response and limits?Maybe I'm wrong and if so I'd love to see real references.Better than 8 bit, sure, I can believe that.Given good enough ADCs  a single $0.10 PY32F002A Cortex-M0 with 48 MHz single-cycle 32x32 multiply and 3 KB RAM is going to beat any analogue computing component costing far more. Multiple GFLOPS chips are available for under $5.Of course it is very good to preserve history, but it making a comeback seems silly. I don't know whether or not the built in ones are, but add on SPI/I2C ones will be

author: rstofer
author_rank: Super Contributor
timestamp: March 08, 2025, 01:57:38 pm
content: If you are using an analog computer to model an Atlas missile at launch, how much accuracy is required? Gimballed rocket nozzles are pretty blunt actuators.Today, the hot setup is MATLAB and Simulink.

author: jonpaul
author_rank: Super Contributor
timestamp: March 08, 2025, 02:25:26 pm
content: Bonjour:In 1950s made a 3 dial bridge like this Edmond, won 1st prize in a Science Fair in Manhattan:By 1964 had the LAST analog computer lab at CCNY, the EAI PACE 231 machine filled an entire air conditioned room, with Burr Brown 12AX7 tube (valve) op amps and pen plotters.a fine museum site....https://www.analogmuseum.org/english/impressions/index.htmlYour thoughts appreciated!Enjoy,Jon

author: munorc
author_rank: Regular Contributor
timestamp: March 08, 2025, 03:08:43 pm
content: Quote from: rstofer on March 08, 2025, 01:57:38 pmInteresting, using a discrete digital approach, simulating an analog system, utilizing a $7k piece of software.This is something that requires a handful of op-amps to model on an analog computer directly.SIMULINK itself is inherently single threaded, although with effort, the problem can be broken up by tasks. Analog computing is inherently parallel.

author: munorc
author_rank: Regular Contributor
timestamp: March 08, 2025, 05:29:10 pm
content: Interestingly, there are many studies and research papers that consider analog computing versus digital computing power efficiency. The estimates are that modern implementations of analog computers are 1000x more power efficient as compared to digital.We are hitting a power density issue in the digital computer realm. I run systems that are high core count systems, e.g. one system is 240 CPU's, 15,000+ cores, 46TB RAM, 2 racks, 150kW. The only way to do this is that we are back to using liquid cooling, DLC (direct liquid cooling). GPU systems are running well over 100Kw/rack. Even with DLC, we are hitting a barrier. Much of the HPC world is nowlooking at single and multi-phase immersion cooling. Each of those CPU's has 90 billion transistors, 10^13 transistors over all.I think the prospect of an analog coprocessor married to an HPC system is quite interesting.

author: rstofer
author_rank: Super Contributor
timestamp: March 08, 2025, 05:49:54 pm
content: Quote from: munorc on March 08, 2025, 03:08:43 pmThe Home (non-commercial, non-academic) version is about $149 for MATLAB and $45 for Simulink. A single copy of MATLAB plays in a lot of domains including Linear Algebra and Machine Learning. But, yes, a couple of quad op-amps will do the job for the Mass-Spring-Damper example.I have a pair of Comdyna GP-6 computers as well as a home-built Vogel computer.https://oldcomputermuseum.com/comdyna_gp6.htmlhttps://www.analogmuseum.org/english/homebrew/vogel/Differential equations are a lot more fun on an analog computer.

author: munorc
author_rank: Regular Contributor
timestamp: March 08, 2025, 06:05:59 pm
content: Quote from: rstofer on March 08, 2025, 05:49:54 pmFrom an Engineers point of view, I agree. In building the analogy/problem, it keeps you closer to the physical system, rather than numerical approaches to integration and solutions to DEQ's.I think they would be valuable as a learning tool as well.

author: munorc
author_rank: Regular Contributor
timestamp: March 08, 2025, 06:14:51 pm
content: Quote from: rstofer on March 08, 2025, 05:49:54 pmI am looking at it more from the realm of Academic and Commercial pricing, since that is the cost to the people that are using it in the real world.In our engineering academic realm, Matlab is one of the largest used application suites across many disciplines.

author: munorc
author_rank: Regular Contributor
timestamp: March 08, 2025, 06:32:02 pm
content: I started off with the past, and we have discussed some aspects of present and future.Living in the present realm. we have THAT.https://the-analog-thing.org/

author: coppercone2
author_rank: Super Contributor
timestamp: March 08, 2025, 06:40:30 pm
content: What is the lowest noise analog computer ever made?For instance one question I have, is why do they use unshielded jumpers.I want to know how much of a improvement could be made if you used the current lowest noise technologies (perhaps modified to work on higher voltage) and heavy spending on shielding.I know its science fiction but I need to know, damnitIf we can do a 100 trillion dollar spending program to get rid of error prompts, we should do it.For instance the LT1028.. low impedance low noise op amp. It gets interesting because of thermal noise from resistors, they do feedback networks like 10 and 50 ohms, instead of like 10k and 5k for a 'conventional' op amp. I thought what if there was stable voltage dividers for really monsterous op-amps that do like miliohm dividers, in the same sense of the lt1028 lower impedance = lower noise.It goes opposite to where we want to bring AC right now (that is, power saving), but I still want to know.The technology is kind of feasible, after all we have op-amps that work as buffers for high resolution ADC's (because of differential to single ended conversion)I often wondered what would happen if you tried to make a op-amp that runs at really low impedance, with like heavy copper and heat sinks, voltage dividers made of power shunts (metal strip bus bar things). I guess that is kind of what Kepco is, in one sense. But, they still apply sanity to like divider network impedance. what would happen if you dropped that requirement?Similar concept to high power shunt regulators. Its absolutely wasteful but it IS a theoretical design choice. I noticed some other non electric systems DO seem to model well as the 'insane shunt equivalent circuit' to common electrical circuits (the problem being massive heat generation)

author: Grandchuck
author_rank: Super Contributor
timestamp: March 08, 2025, 07:20:39 pm
content: Heathkit offered them:https://t-lcarchive.org/heathkit-es-400/I think I saw one at a university a long time ago. I think it was running the bouncing ball demo.

author: Analog Kid
author_rank: Super Contributor
timestamp: March 08, 2025, 08:33:37 pm
content: Quote from: rstofer on March 08, 2025, 01:57:38 pmAnd besides, it worked just fine in the 1960s, so should still work today.

author: TimFox
author_rank: Super Contributor
timestamp: March 08, 2025, 09:42:04 pm
content: Quote from: coppercone2 on March 08, 2025, 06:40:30 pmPerhaps you should use AC, as in WW II servo amplifiers, with transformer or capacitive feedback, avoiding thermal noise in the feedback networks.

author: coppercone2
author_rank: Super Contributor
timestamp: March 08, 2025, 10:12:01 pm
content: did any computers do this?Like benchtop analog computers (general purpose)

author: TimFox
author_rank: Super Contributor
timestamp: March 08, 2025, 10:15:09 pm
content: Quote from: coppercone2 on March 08, 2025, 10:12:01 pmProbably not. Precision pots are much cheaper than ratio transformers, as used in 400 Hz servo systems. Those ratio transformers are very accurate and stable, however.

author: coppercone2
author_rank: Super Contributor
timestamp: March 09, 2025, 12:23:48 am
content: I have one beer size ratio transformerForgot who made it, its concentric dialsa dekatranhow many do you need to make a basic computer system?

author: munorc
author_rank: Regular Contributor
timestamp: March 09, 2025, 01:45:59 am
content: Quote from: coppercone2 on March 09, 2025, 12:23:48 amTegam? ESI?I think ESI was the original, and sold the line to Tegam. IET bought the rights to the resistive dividers, e.g. Dekapot.https://www.tegam.com/wp-content/uploads/2015/10/DT1145-Datasheet.pdf

author: coppercone2
author_rank: Super Contributor
timestamp: March 09, 2025, 02:08:15 am
content: ESII never did much with it because it needs like a enclosure or to be put in a system, it has solder point so its not a benchtop thing. I would need to put it in a boxThen you wonder should it have BNC, Banana or something else connectors and how it can connect to other stuff in lab.oI thought it might be useful as a attenuator for testing homodyne stuff. But making a computer out of it is very interesting

author: rstofer
author_rank: Super Contributor
timestamp: March 09, 2025, 05:37:22 pm
content: With the limited exposure I have to general purpose analog computers, I see that the integrators (low pass filters) tend to have a Tau of 1 second. I don't think a reasonable amount of random noise is going to have much of an effect. There probably aren't any sharp transitions so I wouldn't expect high frequency effects requiring shielded cables. Noise is the reason we use integrators rather than differentiators (high pass filters).Of course, there are always exceptions and we haven't even started talking about component tolerances.I don't expect to get an analytic 'answer' to a DE by way of an analog computer. What I am looking for is how the system responds to various initial conditions and gain settings. Does it converge (damp down toward 0), diverge (ramp up toward 1) or oscillate. I just want to get a sense of what is happening.Vector fields (MATLAB) can provide a better visualization.

author: coppercone2
author_rank: Super Contributor
timestamp: March 09, 2025, 08:17:02 pm
content: we should not give up on efforts to kill the digital computer

author: Andree Henkel
author_rank: Regular Contributor
timestamp: March 10, 2025, 02:47:43 pm
content: the noise of the resistors and computing circuits is usually (my guess) not the limiting factor for achievable accuracy.more important is limited accuracy / tolerance and linearity of Resistors / potentiometers and capacitors to set the systems parameter and starting conditions.0.01% for fixed resistors (about 13Bit) and 1% for fixed capacitors (about 7Bit) is realistic with precision components.Resolution 0.1%, linearity 0.1% requires expensiv 10turn pot.

author: TimFox
author_rank: Super Contributor
timestamp: March 10, 2025, 02:59:08 pm
content: Capacitors above, say, 1 nF are available with better than 1% tolerance.0.1% linearity on 10 turn pots is a practical limit; 40 turn pots can be better, but are now rare.Laser-trimmed resistors can be matched to better tolerance than their absolute tolerance.All of this is expensive, compared with adding bits to a digital system

author: coppercone2
author_rank: Super Contributor
timestamp: March 10, 2025, 09:43:47 pm
content: it could be a generic hybrid you put under a laser to program itlaser trim caps maybe a thing too. Like lets say you make a hole in the PCB and then put a sideways SLCC (single layer) capacitor. Theoretically you can trim it with a laser from both sides even.If you put the cap upright, then its a problem to trim. But if you put it in a hole that goes through the board, it would trim just like the resistors get trimmed. and flip it to do the other side tooDo all the ratiometric trimming when the components are on the PCB, then jumper them with tiny bridges when its all done (very carefully, so no heat is applied to any of the treated parts).. if its high enough impedance then there should be no problem using little bumps of gallium solder to connect it to make sure you minimize thermal ingressSo you can have all the R's and C's within a few percent then put it under a laser with lots of test equipment to match everything, then connect it all together.And there might be tools better then a laser, not sure, thats the easy one. They have ion mills and stuff too.I wonder how good it could get. It depends on how good your laser and test equipment (used to measure the parts) is? I mean theoretically you can add gold atoms one by one to balance the circuit.....?

author: rstofer
author_rank: Super Contributor
timestamp: March 11, 2025, 04:24:37 pm
content: I don't see the day when an analog computer can do textual substitution in a Word document. I rather imagine that spreadsheets are out of the question.The earliest applications for digital computers was calculating artillery trajectories. Analog computers were working fine but digital computers added precision. I still have to wonder, how accurate was the powder charge weight and burn rate? Extra digits doesn't really help a system where ingredients are measured in 'cups' or 'gallons' or 'fill to the line'.It takes some serious math to make a digital computer 'solve' a differential equation. ODE45 is one method, there are others. Why so many? Turns out that digiital computers have problems with DEs. It's worth exploring Google for 'ode45'.