[HN Gopher] Now you're thinking with relays
___________________________________________________________________
Now you're thinking with relays
Author : zdw
Score : 174 points
Date : 2023-11-01 19:30 UTC (1 days ago)
(HTM) web link (lcamtuf.substack.com)
(TXT) w3m dump (lcamtuf.substack.com)
| dekhn wrote:
| lcamtuf, or as I like to call him "imposter syndrome as a
| service" (that's not totally fair; I've caught up to him in many
| ways over the past few years).
|
| Now that I know what a relay is, I can't unhear it. When I plug
| in my EV for charging, I hear the solid click of a (probably
| quite large) relay. When my coffee maker cycles on or off, I hear
| a relay. I don't particularly like it.
| 082349872349872 wrote:
| When I was small, my parents got me a Fischertechnik kit that
| included relays. I still remember the day I discovered that by
| hooking the output of a relay to its input, one could either
| produce stable or instable (cf the Y combinator?) behaviour,
| and the latter produced a relay clicking like mad, as fast as
| its time constants allowed it...
| jacquesm wrote:
| Bonus points for mechanically tuning the relay to give you
| the highest frequency possible. A little screw set into the
| top of the relay casing that pushes down on the arm can make
| the relay substantially quicker (at the price of some more
| contact bounce but that's fine).
| eichin wrote:
| Oooh, flashback to early TRS-80 days - there was an on-
| motherboard relay to control the tapedeck (pause/continue
| transport, you still had to have the buttons pushed down.)
| You could instead drive it fast enough to make (very
| grating) tones, probably damaging it over time (your
| limiting factor was "everyone in earshot trying to make you
| stop", by "grating" I mean "small metal box full of bees"
| :-)
| actionfromafar wrote:
| MSX had the same thing. I played with it a bit but
| worried I might break it :-)
| frabert wrote:
| What you're hearing when your coffee maker cycles on and off
| may actually be a bimetallic strip used as temperature control
| so technically not a relay
| byhemechi wrote:
| Bimetallic strips are pretty slow, I can't imagine them being
| audible. I'd guess what you're hearing is almost certainly a
| relay, very likely driven by the bimetallic strip
|
| edit: Replies have pointed out that they sometimes do "snap",
| so i guess i'm wrong there. I'm still pretty sure anything in
| a kettle/coffee pot/toaster etc would be a relay to avoid
| arcing
|
| edit 2: i'm just going to shut up now
| frabert wrote:
| It's totally possible to shape a bimetallic strip in a way
| that makes it bistable, thus clicking between the two
| states, just like an electrical switch which uses springs
| inside which are normally not noisy either.
| HeyLaughingBoy wrote:
| This is actually the only type that I've ever seen.
| bagels wrote:
| They used to use a coiled strip with a mercury switch on
| the end of it.
| HeyLaughingBoy wrote:
| Right!!! In the old thermostats. I forgot about those.
| aidenn0 wrote:
| One construction I've seen is with a permanent magnet for
| hysteresis; the strip jumps to the magnet when it gets
| close, and then requires extra tension to release. The
| thermostat in my first apartment worked this way (and it
| looked to me like the strip was actually carrying the
| current to operate the gas heater; presumably a NC
| valve).
| quickthrowman wrote:
| Indeed, this is how (non semi-conductor) motor overload
| relays (aka 'heaters') work, a simple bimetallic strip
| with two states.
|
| https://www.c3controls.com/white-paper/what-is-overload-
| prot...
| tgv wrote:
| Also not great for higher voltages and power.
| idiotsecant wrote:
| You can in fact purchase right this very moment
| bimetallic temperature switches for nearly arbitrary
| voltage / current combinations.
| Turing_Machine wrote:
| Right.
|
| Mouser (a general electric/electronic component
| distributor in the USA) has 'em on the shelf rated for
| 600 V, 50 A.
|
| I'm sure that specialty distributors offer a much wider
| range.
| Pathogen-David wrote:
| I've opened up my water kettle before and it uses a
| little bimetalic strip to shut itself off once the water
| is boiling. According to the label it sucks 1500 watts
| and it's just shoving mains voltage through the heating
| coil.
| quickthrowman wrote:
| Bimetallic strips are how motor overload relays work, the
| older ones that are not semiconductors.
|
| This Allen Bradley starter has bimetallic strips capable
| of switching ~600A @ 480v. There are probably bimetallic
| strips that handle even more current:
| https://www.electrical.com/Products/Motor-Control-Allen-
| Brad...
|
| 600A at 480v 3-phase is 500kW
| rcxdude wrote:
| It depends on the kind: a lot of bimetallic strips are
| designed to have hysteresis, so they snap to a different
| shape at one temperature and then stay like that until the
| cool down further (at which point they snap back), and this
| can produce a click.
| sarchertech wrote:
| A bimetallic strip making a noise when it flexes is the
| origin of the original blinker noise. Cars these days just
| emulate the sound, but that's where it came from.
| rjmunro wrote:
| Technology connections covered them as part of this
| video: https://youtu.be/2z5A-COlDPk?t=330
| jacquesm wrote:
| > I'm still pretty sure anything in a kettle/coffee
| pot/toaster etc would be a relay to avoid arcing
|
| You'd be wrong again. The Bi-Metal strip switches the
| current directly.
| byhemechi wrote:
| ahh well, guess i should probably just stop saying
| anything at this point
| dekhn wrote:
| Interesting; I always thought of bimetallic strips as being
| continuous, and silent. I'd open the machine up but
| unfortunately, it's my production coffee maker and the users
| would not be happy if there was downtime.
| dekhn wrote:
| I opened it up, causing a production outage that was noticed
| by the users. Anyway, the relevant part seems to be a Univen
| T250 XB thermostat, but I can't figure out what the
| technology inside is.
| bqmjjx0kac wrote:
| I follow lcamtuf on Mastodon and I am convinced he's made of
| different stuff than I am. A full-time job is enough for me, I
| can't imagine starting (and completing) so many cool side
| projects. To that point, right before this relay madness, he
| wrote up an article in a playable embedded Tetris clone:
| <https://lcamtuf.substack.com/p/mcu-land-part-10-blocks-
| all-t...>.
| dragontamer wrote:
| That PCB mildly triggers me for some reason.
|
| No small 100nF capacitors. Only a bulk 1uF and 10uF capacitor
| inches away. Very inefficient layout. Is that just a 10 Ohm
| resistor connected to a physical switch to control the
| backlight? DC-DC module? He's got a PCB on there already, it
| shouldn't be that much harder to slap down a Buck converter
| himself.
|
| What size components are those? Far larger than 0805, they
| might actually be like 2012 (inch) components.
|
| Good grief. I guess Microchip / Atmel chips are legendary for
| this reason: they always were considered braindead easy to
| boot. But this is the higher-end Cortex-M7 series chips, I'd
| imagine that you'd need at least a _bit_ more care with
| regards to decoupling and power-delivery to achieve
| reliability than what he did here!
|
| No seriously. A 300MHz processor with _NO_ local decoupling
| capacitors? Is he mad?
|
| ------------
|
| But then again, I guess there's something to be said about
| making a board "easier" and through less effort. I guess
| there's no reason to be a masochist with 0603 (or smaller)
| parts when prototyping.
| dekhn wrote:
| He explains all his decisions for PCB design
| (https://lcamtuf.substack.com/p/designing-your-own-pcbs)
| and note this is a small-run device mainly intended for
| pedagogical reasons.
|
| Also the device worked even when it was on a breadboard,
| suggesting he made reasonable technical decisions regarding
| placebo capacitors.
| dragontamer wrote:
| AVR DB is a 24MHz computer though.
|
| This other post (https://lcamtuf.substack.com/p/mcu-land-
| part-3-baby-steps-wi...) has more information with his
| experiments with SAMS70, suggesting experimentation with
| a breakout board. So same same overall but...
|
| He's upgraded to the SAMS70 which is 300MHz. Its a
| totally different class of processor.
|
| > Also the device worked even when it was on a
| breadboard, suggesting he made reasonable technical
| decisions regarding placebo capacitors.
|
| I dunno. PDN (power-delivery network) issues are really
| complex. You solve a lot of headaches with a 1-penny
| 100nF capacitor here and there.
|
| I'm very curious what the SAMS70's onboard capacitance
| is. I'm wondering if Microchip/Atmel goes overboard on
| onboard capacitance or something.
|
| In any case: the documentation from Microchip is clear
| about this. 100nF capacitors on every input pin. I don't
| see any reason to stray from this, its not like 100nF
| capacitors are expensive, or even difficult to solder.
| PumpkinSpice wrote:
| Are you looking at the same thing? There clearly are
| decoupling caps not far from the chip. There's no rule to
| say you need to use 10 x 100 nF capacitors in 0603. They
| are more cost-efficient, but they're more work to solder by
| hand.
|
| The DC-DC module also seems like a sensible choice for hand
| assembly. These things cost about a buck or two these days.
|
| This board is clearly meant to display the electronic
| components in plain view and be easy to solder at home.
| dragontamer wrote:
| > There's no rule to say you need to use 10x 0603 100 nF
| capacitors.
|
| The Microchip documentation for the SAMS70 literally
| recommends 15x 100nF capacitors, as well as a 4.7uF
| capacitor for the buck converter, and a second 4.7uF bulk
| decoupling capacitor.
|
| That's 17x capacitors if you're just following the
| manufacturer's recommendation.
|
| https://onlinedocs.microchip.com/oxy/GUID-174CB4CE-C435-4
| 9E8...
|
| The board as shown in that blog has ZERO of them.
| Madness. Each 100nF capacitor "should" be directly
| adjacent to the power-pin its decoupling, fractions of a
| mm away. And to make sure there's enough room for
| everything to go on (fractions of a mm is very small),
| you want to use 0603, or 0402, or smaller parts just for
| convenience.
|
| But 0603 is already troublesome for hand-placing IMO.
| (though the even smaller 0402 is still possible in my
| experience). So as I said, it starts to get masochistic
| with these sizes IMO. But still, I'd personally try to
| get at least a decoupling capacitor on each power-pin as
| the documents recommend (even if its a larger 0805 or
| bigger).
|
| In any case, the ~4 capacitors that he places is very
| much on the low-end compared to the ~17 recommended.
|
| -------------
|
| > They are more cost-efficient, but they're more work to
| solder by hand.
|
| These are all surface mount parts, which means you're
| soldering using frying-pan and/or toaster-oven at this
| point.
|
| Or at least, you _SHOULD_ be doing that (or maybe get a
| real hotplate, lol. But my pancake electric griddle works
| perfect). Its way more convenient.
|
| You apply the solder paste. Then you drop the capacitor
| into place with tweezers, and the solder-paste is sticky
| enough to "grab" the capacitor. You then place all other
| components. Easy-peasy.
|
| Heat the entire board to 330F (assuming low-melt lead-
| free solder) using the frying pan for 10-seconds and
| done. Some people like adding a 1/4" aluminum plate to
| make the heat more consistently applied.
|
| Components are designed for 500F for 10 seconds btw (aka:
| standard lead-free solder). So you have a lot of leeway
| with regards to the frying pan method in practice. But
| you should keep a strict timer as some parts are really
| sensitive to that "for 10 seconds" requirement. A proper
| reflow oven and/or hotplate obviously does the job better
| with automatic controls, but this is all slow enough that
| you can do it by hand by just turning the dial up/down
| with a stopwatch in your hands.
| Pathogen-David wrote:
| In an EV charger, it's more likely to be a contactor, which is
| similar to a relay but can better deal with high amounts of
| current. (Technology Connections has a video on the differences
| https://youtu.be/VsNHrAzx5_w)
|
| If you want more household relays to notice, it's common to
| find them in digital thermostats for central HVAC control
| signaling. I've also found them inside of ovens, and cars also
| have lots of them for things like the starter and headlights
| (although maybe not the latter in newer cars.)
| dekhn wrote:
| I hadn't heard of contactor but that looks like it's just a
| subtype of relay? And I notice that it says contactors are
| used where relays start to top out, around 15A. Which is
| interesting because the max current I can configure my RAV4
| Prime to is ... 14A. Either way I'm not opening up the little
| portable box that makes this noise. It's clear there's
| something physical clacking in there, not solid state.
| HeyLaughingBoy wrote:
| Yes, the big deal with contactors is that they're designed
| to switch high-current inductive loads. Smaller relays may
| have problems with the arcing caused by a load like a motor
| welding the contacts together.
|
| So, they have bigger contacts to handle the current and
| strong springs and a powerful solenoid to open/close the
| contacts quickly and extinguish an arc before it has time
| to melt anything.
|
| The noise you're hearing is from the contacts opening and
| closing.
| throttlebody wrote:
| Relays and contractors are the same. It's a coil physically
| movin some contacts together to allow current to flow. I got
| no idea why, where or how the naming came about or who
| decides. But i guess its the same as creeks and rivers, when
| does a creek become a river
| matheusmoreira wrote:
| > digital thermostats for central HVAC control signaling
|
| Now I'll never be able to unhear it either!
| scrlk wrote:
| Relay computing taking to the max:
|
| 1958 FACOM 128B Japanese Relay Computer -
| https://www.youtube.com/watch?v=_j544ELauus
| ge96 wrote:
| Nice, Curious Marc has some really good videos like the Apollo
| guidance computer getting taken apart.
|
| The sound of that relay computer churning away dang
| artemonster wrote:
| I have an 8bit relay cpu with 4k word code memory and 256
| register file with banking, this thing clocks at about 20 hz and
| my main problem is looking (and not finding) for interesting
| stuff what I can code on this thing. Even a simple snake game
| with 8x8 dot display is painfully slow, tetris will be
| unplayable. What else? Calculator? A 16bit multiplication runs
| longer that I can count in my head :/
| Aardwolf wrote:
| Sounds interesting, got more info on this cpu? Can one buy it
| or are schematics available?
|
| I wonder if optical or solid state relays can speed it up, at
| least if normally closed ones exist
| 4gotunameagain wrote:
| If you go that way (the non clicky way), might as well use
| transistors :)
| artemonster wrote:
| The point of using relays was for the sound. Reed relays dont
| make loud enough clack and going solid state is pointless,
| you can go directly with transistors then. Regarding more
| info I am very lazy at doing writups and schematics are all
| hand drawn, so its highly unlikely I will ever publish
| anything about it. It has 280 relays, based off two clocks
| with 4 phases (typical latch design from 80s), 12 bit PC, 8
| bit ACC, zero and carry flags, immediate, direct and indirect
| adressing modes. Loud, noisy and totally useless. Memory
| interface is emulated via attached MCU
| gus_massa wrote:
| Posting about this looks like easy karma. I understand that
| writing about the projects takes a lot of time, but if you
| ever have time to do it, my guess is that it will be well
| received here. (Remember to include a video. The first
| thing I did in the current post was to play the video the
| heard the clicks.)
| Aardwolf wrote:
| Well, I think the 16-bit multiplication that takes longer
| than multiplying in your head, at least must sound very
| satisfying then!
|
| So the 4K memory is on a chip, right? (understandable!)
| artemonster wrote:
| Yes, there are two memory IF, one for program (12 addr,
| 16 data) and one for data (8 bit addr, 8 data) and this
| is directly attached to an IO board where MCU emulates
| both rom/ram chips. Additionally, MCU interprets the code
| and checks for expected signals. The added bonus is that
| you can easily add memory mapped io, i.e dot matrix
| display and mcu intercepts reads/writes to certain
| adresses and makes an action (ie toggle led, halt, or
| switch page)
| 4gotunameagain wrote:
| Bitcoin mining ?
|
| Just kidding. Maybe Game of Life ? Minimal arithmetic
| jacquesm wrote:
| Oh neat! How is the memory made, is that using relays as well?
|
| You could make an awesome sorting demonstrator with it where
| the data items themselves move around in the memory.
| ryukoposting wrote:
| When I was in college, I interned with a great German industrial
| automation company. I specifically remember that the programming
| environment we sold to customers included support for "condition-
| coil" logic, AKA "ladder logic." Basically just simulated relays.
|
| For controls guys who had dealt with relays for most of their
| professional lives, that relay-oriented logic flow made sense. A
| typical computer science student's idea of boolean logic gates
| and procedural control flow just wasn't part of their lexicon.
|
| We also offered a graphical, procedural programming language
| (imagine Scratch except it controls part of a factory). You could
| teach it to them, and they'd understand it, but many of them
| never used it. They just wanted relays.
| Tomte wrote:
| > I specifically remember that the programming environment we
| sold to customers included support for "condition-coil" logic,
| AKA "ladder logic."
|
| Yes, the IEC 61131 languages. AWL is a crippled assembler
| language, ST is a crippled Pascal.
|
| Industrial automation is for masochists. The usual explanation
| is that the PLCs need to be programmed by electricians without
| any college degree, but (a) are electricians not stupid and (b)
| would better languages not need to be more complicated.
| contingencies wrote:
| Literally trawling through patents related to electrical
| cabinets right now...
| ryukoposting wrote:
| 61131! I haven't thought about that number in years. Couldn't
| agree with your evaluation more. The sad thing about ST is
| that it was probably the least shitty of the IEC 61131
| languages.
|
| Despite the masochism, it was a fun field to work in for a
| time. Since the industry demands these shitty esoteric
| programming languages, you end up with all these small
| companies writing their own compilers and runtimes. It's a
| unique opportunity to do real-life compiler development from
| the ground up.
| spieswl wrote:
| Some of us even have it on our resumes!
| electroly wrote:
| It was so much worse before 61131. My career in industrial
| automation was on PLCs that predate 61131's existence and had
| no structured text language of any kind. Ladder only. I
| helped write a toolchain that compiles languages similar to
| 61131 (but, again, predating it) down to ladder. I've seen an
| implementation of bitwise floating-point math in ladder that
| no mortal human could possibly understand.
|
| Our experience was not that companies think electricians are
| stupid, but that _they 're electricians_: they know
| electrical stuff, not computer programming. A ladder diagram
| is immediately recognizable to an electrician or technician
| who needs to diagnose an equipment failure and wasn't
| involved in writing the program.
| vvanders wrote:
| You see similar things in HLD languages, from my external
| observation building hardware/gates has a very different
| mental model.
|
| FWIW if you're building something at a certain small scope
| ladder is perfectly serviceable.
| spieswl wrote:
| 61131 has ladder logic, function block, and structured text,
| which is a pretty eclectic group of programming
| representations. I think about 99% of the PLC programs I saw
| were ladder logic, with the exceptions being Siemens pushing
| structured text with a C-like look-and-feel.
|
| Anywho, cool, robust, reliable things still got made, you
| just had to think differently. It was very interesting to
| think about those programs and their relative programming
| simplicity when compared to complex, modern C++ that is
| running in other codebases I've seen since then.
| JoshMcguigan wrote:
| For anyone interested in trying out ladder logic, I run a web
| app that includes a ladder logic simulator in the browser.
| There is a small set of lessons too.
|
| http://www.plcfiddle.com
|
| Sorry it's desktop only for now. I never got around to figuring
| out how to make the drag and drop interface work well on mobile
| screens, although I'd love to.
| MisterTea wrote:
| > For controls guys who had dealt with relays for most of their
| professional lives, that relay-oriented logic flow made sense.
|
| Ladder logic is based on ladder control schematics. They were
| used for machine control circuits to present the circuit as a
| series of rungs running from left to right, the left side
| representing a connection to the control power supply hot or
| positive line and the right represented the control power
| supply return or negative. Each rung is a circuit that handles
| some logic. eg you have a laser machine with three doors and
| two access panels each holding a normally open switch closed to
| complete the circuit - when all the doors are closed the output
| is signal is high which you can use to ensure the doors are
| closed so no one gets melted. The sequence reads top to bottom
| so when you trouble shoot you walk down the steps checking each
| right hand output device and if it didn't work, work your ways
| backwards through the rung with a volt meter.
|
| Way back I got to fix an old Marvell power feed metal cutting
| band saw. All relay logic and the saw would run one cycle,
| retract and do nothing. So I grabbed a meter and the ladder
| diagram and worked my way down until I found a rung with no
| output. Turns out the saw carriage return limit switch bracket
| came loose and the return switch was never pressed which would
| reset another rung to restart the cycle again.
|
| > A typical computer science student's idea of boolean logic
| gates and procedural control flow just wasn't part of their
| lexicon.
|
| Nonsense. I was exposed to industrial automation in high school
| where I was preparing to become an electrician via a robotic
| manufacturing system from eshed robotec. I really liked
| computers but was never interested in programming them at that
| point even though I knew some gw basic and the robots were
| programmed in basic. Then I wound up taking an AP c++
| programming class and it clicked.
|
| To me ladder is a great language and perfect for representing
| the boolean data flow through sensors and switches to visually
| group functions into rungs. It's so much faster to visually
| parse a rung vs a block of text. It's the default on every
| controller for a reason.
|
| Though I'll say this: automation software sucks shit through a
| straw. So much of it was designed on Windows while riding the
| 90s OOP hype train. And the design by committee with languages
| and standards baked into iec/iso standards is depressing.
| 61131-3 defines a crappy Pascal like language called
| "structured text" but everyone bolts on their own oop
| extensions to the language in various proprietary ways. And you
| don't want to begin to fuck with the absolute dog shit
| Byzantine garbage fires that are PLC IDEs. They're so invasive
| that everyone in the biz runs then in VMs so they don't bork
| the OS.
| spieswl wrote:
| Another thing to note is that, depending on the standards
| (e.g. NFPA vs IEC), your control diagrams would be in
| horizontal [0] or vertical [1] format. So the typical left-
| right ladder flow you might see in RSLogix or something
| worked really well with drawings produced to NFPA standards,
| but the mapping broke when given "waterfall"-like schematics
| from a European shop.
|
| You are 100% correct about the tooling being crap and ladder
| representation being useful as a visual mapping.
|
| [0] https://library.automationdirect.com/wp-
| content/uploads/2013...
|
| [1] https://multilinedesigns.com/wp-
| content/uploads/2018/02/IEC-...
| shizcakes wrote:
| Technology Connections very recently put out a walkthrough of
| relay-based logic as it applied to a pinball machine:
| https://youtu.be/ue-1JoJQaEg?si=0iAPDzg5ZHes7Lg4
| andrepd wrote:
| Amazing channel!
| jacquesm wrote:
| This is the real thing:
|
| https://www.youtube.com/watch?v=n3wPBcmSb2U
| Pathogen-David wrote:
| This is dangerous project inspiration...
|
| Also just so nobody misses it in the description, there's a
| whole page with many photos and an additional 1 hour video
| going into more details than the video on YouTube:
| http://web.cecs.pdx.edu/~harry/Relay/index.html
| jacquesm wrote:
| Links should have a 'nerdsniping advisory' tag.
| XorNot wrote:
| Seriously: I was watching that feeling myself get the "of
| course I should have this on a wall in my house..." feeling.
| jacquesm wrote:
| It's a good thing the only blank wall in my work room
| doesn't have any outlets near it.
| Scene_Cast2 wrote:
| Slightly off topic, but would anyone know how to make PCB routing
| look smooth and curved like that? The screenshot looks like it's
| the 3D KiCad viz, but KiCad doesn't have that functionality by
| default.
| thousandknives wrote:
| https://github.com/mitxela/kicad-round-tracks
| Workaccount2 wrote:
| Wow, I essentially did this same project a number of years ago,
| but never finished it. My ship ran aground debugging division
| since it becomes long and convoluted to do it, especially when
| also dealing with negative numbers and decimals.
|
| I also added an LED board that was an array of LEDs, one LED per
| relay, attached to it's coil. This way you could see the states
| of the calculator flash by as it computed, akin to those old
| blinking button boards of retro sci-fi. Really neat project!
| mikewarot wrote:
| 4PDT relays might seem exotic now, but they are quite common when
| you're working on old radios, etc. As for carrying through
| complementary signals, that's a good hack.
|
| There is a type of logic using Micromachined Silicon cantilever
| switches, operated by static voltages, capable of operation for
| sustained periods. They don't seem to have achieved fully non-
| volatile operation, but you can spend a lot of money to have a
| relay of this type, if you want.[1]
|
| At one point I was hopeful this would replace relay logic, and be
| even lower power than CMOS.
|
| [1] https://www.qorvo.com/products/p/CMD235C4
| xw3090 wrote:
| They're still in use.
|
| i.e. https://www.digikey.com/en/products/filter/signal-relays-
| up-... has 811 hits.
|
| According to the datasheets:
|
| Typical applications Industrial sewing/stitching machines,
| fitness, elevators, pumps, robotics, solar panels
| zug_zug wrote:
| If you think this is fun you might enjoy MHRD - a game about
| building a gradually building up to functioning CPU using only
| logic gates (i.e. transistors/relays).
|
| You can have all the puzzley fun of it without any soldering etc.
| Graziano_M wrote:
| Also nandgame.com which is basically a game version of the
| excellent nand2tetris game.
| HeyLaughingBoy wrote:
| I was in my mid 20's when I was sent by my company to give a
| short training course to a civilian group that worked for the US
| Army Signal Corps at Fort Gordon. These guys built simulators of
| the big field radios that the signalmen carried around and
| _everything_ was done with relay logic. This was the mid 90 's
| and it blew my mind: I'd heard of relay logic in some EE course
| or the other, but I'd never actually seen it in operation. It's
| one thing to understand what's theoretically possible; quite
| another to actually see combinatorial and timing logic executed
| by loudly clacking relays. But it worked!
|
| They used relay logic because it's what they knew: some of them
| had backgrounds in industrial control. The small company I worked
| for sold single board computers and the group leader knew that
| there had to be a better, more modern method of building their
| simulators, so they asked to have someone sent down to educate
| them. That someone was me. I probably did a piss-poor job of it
| (no experience or aptitude for training at the time) but I hope
| it at least set them on the right path.
| chrisdhoover wrote:
| I had the good fortune to go inside a Pac Bell switch. Inside
| was an entire floor of 2-post relay racks housing... wait for
| it... relays. The click clacking was music to my ears. Phone
| system switching predated transistors and computers.
|
| Weren't early MIT based SWE also model railroaders? I think
| there is some connection there between model railroad
| switching, relays and logic.
| eichin wrote:
| http://tmrc.mit.edu/history/ has model trains, relays, and
| PDP-11s :-)
| pugworthy wrote:
| I love that sound. It makes me think of mechanical keyboards and
| "hacking" terminals in the Fallout games.
| nielsbot wrote:
| I should find my schematics--
|
| When I was younger straight out of college I designed a digital
| clock that was relay-based. I made a 0-16 counter circuit on one
| board and a 10-reset circuit on another board. I didn't have 4
| pole relays, just 2 pole, but I did try to make use of a mix of
| normally open (N.O.) and normally closed (N.C.) to keep the parts
| count low. The binary-to-7 segment logic was to be implemented
| using a diode ROM.
|
| I had the same idea about using clear relays--so you could see
| the parts working, but I couldn't find those at the local
| electrics shop, so I instead just took the plastic housings off
| of standard relays.
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