How Do You Build a Relay CPU?

relay

The Hackaday tips line is always full of the coolest completed projects, but only rarely do we see people reaching out for help on their latest build. We’ll help when we can, but [Tim]’s relay-based CPU has us stumped.

[Tim] already has the design of his relay CPU completed with a 12-bit program counter, sequencer, ALU, and a transistor-based ROM. The problem he’s having deals with the mechanics and layout of his homebuilt CPU. Right now, all the relays (PC pin, we guess) are glued top-down to a piece of cardboard. This allows him to easily solder the wires up and change out the inevitable mistakes. This comes with a drawback, though: he’s dealing with a lot of ‘cable salad’ and it’s not exactly the prettiest project ever.

The ideal solution, [Tim] says, would be a PCB with through-hole plating, but this isn’t easy or cheap for the home fab lab. We’d suggest some sort of wire wrap setup, but proper wire wrap sockets and protoboards are for some reason unreasonably expensive.

If you have an idea on how to do the mechanical layout and connections of a relay-based computer, drop a note in the comments. [Tim] has a very cool project here, and it would be a shame if he were to give up on it due to a lack of tools.

Video below, and if you’re having a problem with a project, feel free to send it in.

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Rotary phone museum exhibit

dial-telephone-museum-exhibit[David Burroughs] wrote in to share this dial telephone museum exhibit he built and we’re glad he did because we love interactive museum hacks. He mentions that it’s not really tied to the theme of the Roads and Rails Museum in which it’s installed. But when we think of railroad history we also think of telegraph. And that’s just a hop, skip, and a jump from telephones.

The display allows museum goers to play with the rotary dial on the phone. The box next two it contains a 10-position relay increment switch. So each pulse from the dial increments the switch. There’s a satisfying click, a moving arm, and different colored LEDs which highlight the inner workings. An Arduino board monitors the phone, displaying the dialed number on a seven segment display then incrementing the relay.

We figure the interesting part is to see that telephony used to use mechanical switching like this. But the video below includes a story about the kid who asked how you carried this phone around. This brings to mind the phrase “hang up the phone”, which doesn’t have the same literal meaning it used to.

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Water heater controller automates garage doors

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The black box mounted between two garage doors is actually a water heater controller. The entire assembly is a conglomeration of hacks which [Simon] added to his garage over the last four years. We’ll give you a quick rundown, but the entire story is told in his blog post.

Back when the house was built [Simon] was approached by the contractor who offered to throw in remote control for the garage door rollers for just 1500 Australian Dollars (about $1350 with today’s rates). That sounded quite steep to him. He managed to add his own remote control for about a third of the price. But there were a few missing features. Notably, a lack of a light that comes on when the doors open. He also didn’t like that the button inside the garage was on the motor, which is mounted quite high.

Years later his water heater controller needed a firmware upgrade from the manufacturer. Check this out: they replaced the entire controller rather than flashing the PIC 18F2321 inside. What a waste! But in this case [Simon] snagged the old unit, which included several mains rated relays. He connected one up to a light socket seen above, and outfitted several illuminated buttons on its original enclosure. Now he has the satisfaction of a light that comes on with when the door opens,  and shuts itself off after a preset delay.

Now his daughter wants smartphone control. But that’s as easy as hacking a Bluetooth headset.

Complicated iPhone garage door opener

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The round-about way this iPhone garage door opener was put together borders on Rube Goldberg. But it does indeed get the job done so who are we to judge? Plus you have to consider that the Apple products aren’t quite as hacker friendly as, say, Android phones — so this may have been the easiest non-Jailbreak way.

The main components that went into it are the iPhone, a Wemo WiFi outlet, and a 110V rated mechanical relay. But wait, surely it can’t be that simple? You’re correct, just for added subterfuge [Tall-drinks] rolled IFTTT into the mix.

You may remember hearing about If This Then That from the Alert Tube project. It’s a web-based natural language scripting service. Throw everything together and it works like this: The iPhone sends a text message which IFTTT converts to a Wemo command. A power cord connects the Wemo outlet to the 110V electrodes on the relay. The normally open connection of the relay is attached to the same screw terminals of the garage door opener as the push button that operates it. When the relay closes, the garage door goes up or down.

The biggest problem we have with this is the inability to know if your garage door is open or closed.

ATX Raspi is a smart power source for Raspberry Pi

One aspect of the Raspberry Pi that has always challenged us is the power supply. It was a great idea to power the board from a standard micro-USB port because economy of scale makes phone chargers (even in the 1A range necessary for stable operation of the RPi) cheap and easy to acquire. The thing we miss is the ability to power the device on and off using the built-in hardware. The quandary has given rise to many different solutions, and the ATX Raspbi smart PSU is one of the better ones we’ve come across. It’s a nicely packaged take on the PIC-based version we saw earlier in the year.

The device is a small PCB that acts bridge between the micro-USB power supply and the RPi board. It offers several breakout headers, one of which is used for a power button. The button is monitored by a microcontroller that switches the on-board relay accordingly. But it won’t just kill the power when you want to shut down. It first signals one of the RPi GPIO pins, causing the OS to execute a shutdown script. It then monitors the RPi for the shutdown tasks to finish before cutting the power.

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Rattle generator is a new type of dynamo for a bicycle

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This project is in one of our favorite categories; the kind where asking “why?” is the wrong question. [Berto A.] built the device after observing some power generation by placing a large magnet next to a mechanical relay coil and quickly clicking the relay’s lever. From this humble beginning he built up the RattleGen, a bicycle spoke driven generator.

To get the most power possible he searched around for a massive relay and found one which was originally meant for telephone exchanges. He cut the case open and strapped a big bar magnet to the side of the coil. Next he fabricated an arm which will press against the relay’s lever. To that he added a small wheel which is pressed each time a spoke from the bicycle passes by it. This repeated clicking of the relay lever generates a current (and a rattling sound) that is harvested by the joule thief circuit built on some protoboard. An LED is illuminated, with excess current stored in the capacitor bank. Don’t miss the build and demonstration video after the break.

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Network-controlled fireworks launcher

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[Thomas] and his friends wanted to ring in the new year by setting off some fireworks. To keep a safe distance and have a little fun they built this network controller launcher (translated).

the image on the left shows the build in its unused and pristine state. But by the end of the celebration it look a bit melted and burnt. Still, for the first revision of the system it ended up working pretty well.

We’ve seen several remote fireworks launchers that burn up resistors to light the fuses. But this system is much more reusable. The image on the right shows the heating elements which light the fuses. Younger readers might have no idea what they’re looking at, but every automobile used to come with at least one of these electric cigarette lighters. Just drive 12V through them and they get burning hot relatively quickly. That’s where the car battery on the base comes into play. It is connected to the lighters using some mechanical relays.

In the food container attached to the side of the launcher you’ll find a Raspberry Pi which provides the web connection for the system. [Thomas] wrote code which uses a webpage with some bomb icons as buttons. Check out the video after the break to see him demonstrate how fast one of these lighters will glow red after pressing a button on his smart phone.

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