Thank you so much everyone, this is something I've worked on for a few years on and off -- I posted about it here in a Show HN a few hours ago [0]
The biggest unlock was finding Willy McAllister's excellent Circuit Sandbox [1], which provides the Minivac Simulator's underlying electrical math. I tried so many approaches to simulate electricity (a doomed DIY approach, Falstad, Spice...) but Circuit Sandbox's DC analysis did the job perfectly.
Ping me for questions, and would love to read your feedback!
Thanks for making this! Love the manuals too. It reminds me of the Radio Shack 150-in-one electronics kit I had as a kid.
Super cool. And thanks for links to the original manuals for those that want to take a deep dive.
Feature request: I was wanting for a bit more sound… I mean, when I see "relay computer", I'm heading there for lots of soft clicks.
More…?! :)
I totally feel you - the one reservation is that I’m using (gasp) not the original Minivac Relay sound. I need to go to a Computer Museum that will let me record one to offer a more authentic simulated experience.
So tldr - let me get a clean real sound and then we can come back to this question :)
You may not need to get a museum's cooperation. After a quick search it seems these come up for sale from time to time. I saw one on the Vintage Computer Federation forums offered in 2021 for $500. You may be able to find a collector online who has one and will record the relays for you. A lot of folks have pretty high-quality USB mics for conferencing/podcasting these days.
An alternative might be going to a regional VCF show where one will be (possibly by pre-arrangement with a collector). There are five or six shows held around the country every year. Unlike a museum almost all the devices there are available for hands-on interaction.
I heard some clicks. I thought they were just the sounds of the switches I was toggling. Are there other (relay) sounds I somehow missed?
Just to make sure I'm not misunderstanding:
The relay click sound you're hearing should only happen when a relay turns on, and when it turns off. There is no sound when a button is pressed - you can check this by loading an empty simulator and pressing any of the buttons at the bottom (the simulator won't make any sound):
https://minivac.greg.technology/simulator/
((Once/if I get to see a Minivac in real life, I may learn that buttons do make sounds..))
When a relay turns on and off, a sound is played. In the following circuit, check this by pressing and releasing the button 1:
https://minivac.greg.technology/simulator/#wires=1%2B%2F1C%2...
Do NOT overlook the manual .PDFs. They are crazy awesome. These people cared about what they were doing.
well the fact that you can wire the Rotary Switch to power and the thing physically rotates --- that's definitely Haptic Feedback that i dont ever recall seeing in a computer. lol.
that manual is wild too. entire section on games.
reminds me a lot of those old radioshack "build your own circuit" boards. the wires to components especially but also the manual, the way it just builds up dozens of examples from simple to complex, so if you really wanted to, a child could work their way through it slowly and understand everything.
looks like the inflation adjusted cost would be around 900 bucks today.
The Rotary Switch - which is both input and output in the real Minivac - is absolutely wild yeah.
One of the crucial things I didn't get to yet is making that wheel controllable - some circuits in the manuals do require you to turn it. That's high in the todo list (with mobile support).
I also really want to share all of the videos I've been collecting of similar "wheels" - in (modern-ish) elevators [0] and light shows [1]... And also pinball machines! [2]
Re: RadioShack boards, I did have the "300 in 1" kit growing up, so yes... it's full circle for me. :-)
[0] https://www.instagram.com/reel/C3dk5GkJni6/ and https://www.instagram.com/reel/CzuHXKRpuN-/
"Before microchips existed, computers were built with mechanical relays." Should probably say something about vacuum tubes as well!
And discrete transistors. Now that my curiosity is piqued, I found this nice timeline:
https://www.computerhistory.org/timeline/computers/
It looks like transistorized computers were dominant at the point when integrated circuits were introduced.
Interesting: the entry for the Apollo Guidance Computer (AGC) indicates it used integrated circuits—I had remembered hearing it used RTL (resistor-transistor logic).
It turns out both are true [1]. The "integrated circuits" were sort of "flat-packs" of RTL circuits. I had forgotten that early IC's were not quite what we envision today. Regardless I suppose ICs were RTL before they were TTL (before they were CMOS, etc.).
[1] https://en.wikipedia.org/wiki/Apollo_Guidance_Computer#Logic...
In particular, the IBM 1401 (two of them actually) that you can see demonstrated at the Computer History Museum in Mountain View are transistor-based and were very successful computers.
And before that with gears! (With limited success.)
Indeed, my dad was a research scientist at a large chemical company, and every scientist had a Friden mechanical calculator, which was capable of multiplying and dividing. But it was not a programmable computer.
When the HP 35 came out, it was cheaper than the annual maintenance contract for the Friden. They bought one, and passed it around to try out for a week, then all of the Fridens went into the dumpster. Of course he brought one home, and we got to play with it.
Ha ha, the rich kids when I was in high school Physics had these calculators. It was the first I had seen them. At over $100 (as I recall) they were completely out of reach for me and half the class.
(Ands they had to either have an extra set of batteries handy or access to an outlet to plug in the cord since the possibility of the batteries dying during a test was a real likelihood.)
[dead]
I like how the 1937 "Model K" adder is literally on a breadboard.
(are those knife switches in the upper right?)
U-type flat spring, see fig 2, precursor to transistor
https://www.calling315.com/relay-logic
The user facing switches are 'A' & 'B'
When you attach a name as inventor of something, it sounds as if the whole concept was borne by them, which is not true. All "inventors" and "great leaders" are only carriers of incremental change, which sometimes marks a milestone for a series of changes done by their predecessors or the context.
Steam engine concepts were already there before Jame Watt, logic by electrical circuits was already there before Shannon. People provide incremental guidance for the change, like river banks do to the flow of the river. No single part of the river brought the river upto that point.
There are many cases when the incremental change that is due to an individual inventor is very clearly defined, so it is known precisely which is the contribution beyond what was inherited from the predecessors.
For that incremental change, the name of its inventor is appropriate.
However, you are right that too frequently people fail to distinguish what was new and what was old in an invention, and they misleadingly attach the name of the inventor/discoverer to the entire big system or theory, not to the small features that are truly new.
The inventors or discoverers are frequently guilty of this themselves, by failing to properly acknowledge their sources and by making exaggerated patent claims, which nowadays are too frequently accepted by patent offices that do not perform an adequate search of prior art.
It says, "Designed by Claude Shannon" (at least now it does) - did it formally say invented or what's put the bee in your bonnet?
shameless plug https://github.com/artemonster/relay-cpu a great and useless hobby project :) 10/10 would do again
Very cool. I've been sketching out a relay computer myself. Mostly unbuilt but I have tested a variety of circuits implementing gates, latches, oscillators, flip flops, counters, registers all using only SPST reed relays.
I'm fixated on speed. I connected some reed relays in a 3 stage ring oscillator and it ran at 1.8 kHz. That has me thinking that with a pipeline 100 instructions a second might be attainable. Reed relay logic seems to be fast enough for a UART at 50 baud. Teletype interactivity is a stretch goal.
My program counter is also 12 bits! And I've also been using Digital to simulate parts of it. Great tool for that.
The current design is RISC-like with a 12 bit word requiring 4 cycles for most instructions. I have an old version of the design specified in gate level Verilog. I should publish that. Though I'm forever tinkering with the control such that it'll probably never be done. Karnaugh maps are like Sudoku.
Oscillator can go high, but real logic is complex and requires realiability. and the fact that cheap relays are absolute crap with a ton toff spread between 3ms to 18ms! The actual clock frequency you can hope for is around 10-15 hz :(
It's almost hard to believe this is possible now in a modern web browser. It's a really sublime thing and I'm glad someone figured out a way to do this. I remember Web 1.0 before the days of JavaScript and P.H.P. allowed interactive websites... Indeed, it's entirely different now.
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Here's a demonstration of a 1958 relay computer.
Thanks!
The Enigma-cracking Bombe (on display at the extraordinary Bletchley Museum of Computing) also used relays
https://www.tnmoc.org/bh-10-bombe-description
And the Z3 as well!
IBM SSEC, which has started operation at the beginning of 1948, has been for a few years the fastest and most versatile computer in the world (unlike the special-purpose ENIAC) and it has solved a great number of important problems of scientific and technological interest.
It was a hybrid electronic-relay computer, containing more than twenty thousand electromechanical relays and more than ten thousand vacuum tubes.
This is likely the biggest and most complex relay computer ever made, though its main arithmetic part and its fastest registers were made with vacuum tubes, for increased speed in comparison with a pure relay computer.
Relay computers must have been pretty loud with all those clacking mechanical switches.
They were, and some are still in use in legacy traffic control systems.
Ah yes, I have a stack of these; lovely things for kids to learn some basic stuff. They are the oldest systems I own and they still work (they are fairly easy to fix).
Amazing! I don’t think I’ve heard of anyone owning many..!
1) Are any of them for sale? :)
2) Would you be open to recording a clean sound of one of its relays turning on and off? And helping me figure out some specifics about the motor wheel (its speed and whether it experiences any speed up)
Thank you! My email is:
hi at greg.technology
I am currently on vacation, but when back I will contact you.
I imagine it would be easier for me to build the simulator than to make it do anything of interest.
While snarky, I see where you're coming from. Sometimes a lot of the fun is in the building of a thing to understand how it works. Learning how a thing works from the user-facing side of the control panel is, for some of us, less rewarding.
If anything though, I want to go build a physical relay computer mechanism myself now (if even just a 4-bit adder or something).
Ha, I really get the sentiment! I do recommend perusing the Book 1 manual [0], towards the end there are a number of small problems (on page 30). They're worth tinkering with :-)
[0] https://minivac.greg.technology/manuals/1961-minivac601-book...