If you thought your home-brew project was taking a long time, [Jeroen Brinkman]’s MERCIA Relay Computer project probably has you beat. He began working on this impressive computer back in 2014, and has been at it ever since. In fact, the ongoing nature of the project is embedded into the name itself — the English translation of the acronym MERCIA is “My Simple Relay Computer Under Construction”. Being interested in old analog and relay computers from an early age, [Jeroen] took on this project to educate students about how computers work. The entire computer is build only using relays, diodes, and capacitors, not to mention color-coded wire based on signal functions. Using relays as the primary switching elements is at the core of his educational goal — anyone can understand how a relay works.
Understandably, this thing is big. But he has cleverly packaged it to visually show the major building blocks of a computer. While the exact size isn’t stated, we can estimate based on the photo of [Jeroen] standing next to the modules that these panels are about 1.5 m tall and perhaps 60 cm wide. The whole computer is nine panels wide, making it about 5 meters long. Except for the ROM assembly, pairs of panels are hinged together and they fold like a book and carried like a suitcases when being moved. If you enjoy the clickety-clack sound of relays, be sure to watch the relay longevity test in the video below and check out our article on the 1958 FACOM from last year.
This is a fascinating project, but unless you have a couple thousand relays laying around and a decade of free time, it’s probably better to just enjoy [Jeroen]’s work rather than build your own. We hope he releases schematics and other documentation once the project is finished. You can follow his Facebook build log if you want to keep track of the progress. Thanks to [David Gustafik] for the tip.
When it comes to understanding computers, sometimes it’s best to get a good understanding of the basics. How is data stored? How does the machine process this information? In order to answer these questions a bit more and start learning programming, [Nakazoto] built a 10-bit binary adder with relays.
The build is designed from the ground up, including the PCBs, which are milled using a CNC machine. There are six boards: the input board, sequencer board, 2 sum register boards, a carry register board and a 1-bit ALU board. The input board has 32 LEDs on it along with the switches to turn on each bit on or off. In total, 96 relays are used and you can hear them clacking on and off in the videos on the page. Finally, there is a separate switch that sets the adder into subtraction mode.
Usually, [Nakazoto]’s website is mostly about cars, but this is a nice diversion. The article has a lot of detail about both the design and build as well as the theory behind the adder. Other articles on binary adders on the site include this one which uses bigger relays, and this 2-bit adder which uses 555 timers.
Imagine having to program your computer by rewiring it. For a brief period of time around the mid-1940s, the first general-purpose electronic computers worked that way. Computers like ENIAC initially had no internal storage for code. Programming it involved manipulating thousands of switches and cables. The positions of those switches and cables were the program.
Kathleen Booth began working on computers just as the idea of storing the program internally was starting to permeate through the small set of people building computers. As a result, she was one of the first programmers to work on software and is credited with inventing assembly language. But she also got her hands dirty with the hardware, having built a large portion of the computers which she programmed. She also did some early work with natural language processing and neural networks. And this was all before 1962, making her truly a pioneer. This then is her tale.
The humble car alarm has been around almost as long as the car itself, first being developed by an unknown prisoner in Denver, circa 1913. To the security-conscious motorist, they make a lot of sense. The noise of a car alarm draws attention which is the last thing a would-be thief wants, and the in-built immobilizers generally stop the car being moved at all without a time-consuming workaround. Both are a great deterrent to theft.
It may then surprise you to know that I, dear readers, consider the aftermarket car alarm to be one of the most heinous devices ever fitted to the modern automobile. Combining the unholy trifecta of being poorly designed, cheaply made, and fitted by only the most untalented or uncaring people to wield a soldering iron, they are a blight that I myself refuse to accept.
It was my very own Mazda that suffered at the hands of a car alarm system. Two days after purchasing the car, the keyfob died, and thus the car would no longer start. My other car was already out of action due to bent valves, and I needed to get to work, so I figured as a competent hacker, I’d be able to quickly disable it.
Recently, [Manuel] did a post on making logic gates out of anything. He mentioned a site about relay logic. While it is true that you can build logic gates using switch logic (that is, two switches in series are an AND gate and two in parallel are an OR gate), it isn’t the only way. If you are wiring a large circuit, there’s some benefit to having regular modules. A lot of computers based on discrete switching elements worked this way: you had a PCB that contained some number of a basic gate (say, a two input NAND gate) and then the logic was all in how you wired them together. And in this context, the SPDT relay was used as a two input multiplexer (or mux).
In case you think the relay should be relegated to the historical curiosity bin, you should know there are still applications where they are the best tool for the job. If you’re not convinced by normal macroscopic relays, there is some work going on to make microscopic relays in ICs. And even if they don’t use relays to do it, some FPGAs use mux-based logic inside. So it’s worth your time to dig into the past and see how simply switching between two connections can make a computer.
How do you go from a two input mux to an arbitrary logic gate? Simple, if you paid attention to the banner image. (Or try it interactive). The mux symbols show the inputs to the left, the output to the right and the select input at the bottom. If the select is zero, the “0” input becomes the output. If the select is one, the “1” input routes to the output.
[Mark Gibson] probably has nothing against silicon. He just knows that a lot that can be done with simple switches, relays, and solenoids and wants to share that knowledge with the world. This was made abundantly clear to me during repeat visits to his expansive booth at Denver Mini Maker Faire last weekend.
In the sunlight-filled atrium of the Museum of Nature and Science, [Mark] sat behind several long tables covered with his creations made from mid-century pinball machines. There are about two dozen pieces in his interactive exhibit, which made its debut at the first-ever Northern Colorado Maker Faire in 2013. [Mark] was motivated to build these boards because he wanted to get people interested in the way things work through interaction and discovery of pinball mechanisms.
Most of the pieces he has built are single units and simple systems from pinball machines—flippers, chime units, targets, bumpers, and so on—that he affixed to wooden boards so that people can explore them without breaking anything. All of the units are operated using large and inviting push buttons that have been screwed down tight. Each of the systems also has a display card with an engineering drawing of the mechanism and a short explanation of how it works.
[Mark] also brought some of the original games he has created by combining several systems from different machines, like a horse derby and a baseball game. Both of these were built with education in mind; all of the guts including the original fabric-wrapped wires are prominently displayed. The derby game wasn’t working, but I managed to load the bases and get a grand slam in the baseball game. Probably couldn’t do that again in a million summers.
A PS-3 controller has an unbalanced motor inside that vibrates your hand whenever you crash a car into a wall or drive it off a cliff and hit the rocks below but [Rulof Maker] wanted that same feeling all over his body. So he added a serious unbalanced motor to his favorite gaming chair to make his whole body vibrate instead.
To do that he opened up the controller and found the wires going to the unbalanced motor. There he added a small relay, to be activated whenever the motor was energized. Wires from that relay go to a female connector mounted in the side of the controller, keeping the controller small and lightweight.
Next he needed to attach a much bigger unbalanced motor to the underside of his favorite gaming chair. For the unbalanced mass he poured concrete powder and molten lead into a tin can mold and attached the result to the motor’s shaft. Using a piece of wood he attached the motor to the chair’s underside.
All that was left was to power the motor and turn it on when needed. For that he wired up a bigger relay, with the relay’s coil wired to a male connector to plug into the PS-3 controller. Now when the PS-3 wants to vibrate, that relay is energized. All that was left was to wire the relay’s normally open switch, the motor and a power cord in series, plug it into the wall socket, and he was ready to shake.