[HN Gopher] A 1961 Relay Computer Running in the Browser
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A 1961 Relay Computer Running in the Browser
Author : vaibhavsagar
Score : 133 points
Date : 2025-11-17 02:36 UTC (20 hours ago)
(HTM) web link (minivac.greg.technology)
(TXT) w3m dump (minivac.greg.technology)
| etaioinshrdlu wrote:
| "Before microchips existed, computers were built with mechanical
| relays." Should probably say something about vacuum tubes as
| well!
| analog31 wrote:
| 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.
| hbrav wrote:
| And before that with gears! (With limited success.)
| analog31 wrote:
| 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.
| JKCalhoun wrote:
| 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.)
| aebtebeten wrote:
| I like how the 1937 "Model K" adder is literally on a
| breadboard.
|
| (are those knife switches in the upper right?)
| JKCalhoun wrote:
| 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#Lo
| gic...
| ebruchez wrote:
| 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.
|
| https://computerhistory.org/exhibits/ibm1401/
| don-bright wrote:
| 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.
| gregsadetsky wrote:
| 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-/
|
| [1] https://www.instagram.com/reel/C6qqCdhJbM2/
|
| [2] https://www.youtube.com/watch?v=ue-1JoJQaEgm
| ljsprague wrote:
| I imagine it would be easier for me to build the simulator than
| to make it do anything of interest.
| gregsadetsky wrote:
| 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...
| JKCalhoun wrote:
| 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).
| gregsadetsky wrote:
| 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!
|
| [0] https://news.ycombinator.com/item?id=45945762
|
| [1] https://spinningnumbers.org/a/circuit-sandbox.html
| JKCalhoun wrote:
| 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.
| gregsadetsky wrote:
| 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 :)
| JKCalhoun wrote:
| 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?
| gregsadetsky wrote:
| 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%2F1
| C%2...
| mrandish wrote:
| 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.
| mrandish wrote:
| 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.
| zkmon wrote:
| 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.
| adrian_b wrote:
| 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.
| djmips wrote:
| 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?
| CamperBob2 wrote:
| Do NOT overlook the manual .PDFs. They are crazy awesome. These
| people cared about what they were doing.
| saharasara wrote:
| Relay computers must have been pretty loud with all those
| clacking mechanical switches.
| cluckindan wrote:
| They were, and some are still in use in legacy traffic control
| systems.
|
| https://youtu.be/YDU47MxfHnQ
| anonzzzies wrote:
| 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).
| gregsadetsky wrote:
| 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
| anonzzzies wrote:
| I am currently on vacation, but when back I will contact you.
| suckow wrote:
| 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.
| bolangi wrote:
| Here's a demonstration of a 1958 relay computer.
|
| https://youtu.be/_j544ELauus?t=373
| gregsadetsky wrote:
| 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!
|
| https://en.wikipedia.org/wiki/Z3_(computer)
| adrian_b wrote:
| 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.
|
| https://en.wikipedia.org/wiki/IBM_SSEC
| artemonster wrote:
| shameless plug https://github.com/artemonster/relay-cpu a great
| and useless hobby project :) 10/10 would do again
| retrac wrote:
| 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.
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