4-bit Adder Built from Mechanical Relays


Would you consider this to be doing math the old-fashioned way? Instead of going with silicon-based switching (ie: transistors) this 4-bit adder uses mechanical relays. We like it for its mess of wires (don’t miss the “assembly” page which is arguably the juiciest part of the project). We like it for the neat and tidy finished product. And we like it for the clicky-goodness which surely must bloom from its operation; but alas, we didn’t find a video to stand as testament to this hypothesis.

The larger of the two images seen above is from the register memory stage of the build. The black relay in the bottom right is joined by a ring of siblings that are added around the perimeter of the larger relays before the entire thing is planted in the project box.

Sure, simulators are a great way to understand building blocks of logic structures like an adder. But there’s no better way to fully grip the abstraction of silicon logic than to build one from scratch. Still hovering on our list of “someday” projects is this wooden adder.

[Thanks Alex]


Wireless AC Control With The Raspberry Pi

We’ve seen some of [Connor]’s work before, and it looks like he’s now turning to product design. He’s come up with an adapter for the Raspberry Pi to control a few wireless wall socket relays, allowing anyone with a Pi to control lights, coffee makers, TVs, and anything else that falls under the very broad home automation banner.

The system uses a 315MHz radio breakout board for a Raspberry Pi to control the relays in one of three wall socket adapters. There’s a script running on the Pi with a very nice GUI to turn the lights on and off.

[Connor]’s product is extremely similar to a certain WiFi-enabled wall-plug relay system controlled by a smartphone, and to that end, he’s decided to call his device the Belchin’ Emo Switch. The name might need work, but he’s selling three Raspberry Pi-controlled wall plugs for the same price of one wall plug from Brand A.

Below you’ll find [Connor]’s videos for his device. You can also check out this reddit thread where he shows off just how open source he can be; there are part suppliers and even how he’s packaging this system for shipment.

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Meltinator 9000 Fuses Glass by Degrees

kiln[Richard]’s wife scored an Evenheat glass-fusing kiln, but the 20-year-old temperature controller was broken. He could have simply ordered a replacement controller, but that kind of problem solving doesn’t get you on Hack a Day. His wife wanted more control over the kiln and he convinced her that building their own was the way to go. Thus, the Meltinator 9000 was born.

[Richard]’s design uses an Arduino Uno and an Adafruit display shield, protoshield, and thermocouple reader board. He built a simple relay driver with a resistor, BJT, and a diode and connected it to pin 13 and its built-in indicator. To [Richard]’s delight, all of this fit in the original enclosure.

[Richard]’s software provides 25 fusing schedules with ten steps apiece. Each step has a target temperature,  rate of temperature change, and a hold time which can be increased on the fly. He ran a test program that heated the kiln to 1500°F at a rate of 2550°F/hour. He then cooled it to 500°F at a rate of 1000°F/hour, which took longer than he thought. The good news is that the kiln is well-insulated!  [Richard] has the software available on his GitHub.

Don’t have a glass kiln? Prefer to control beer-related temperatures? You could always hack your stove in the name of homebrewing.

How to Stop Grandma’s Wheelchair If She Goes Out of RC Range

Okay, so he doesn’t have Grandma riding in it that we know of, but [zim] recently decided to turn a Jazzy mobility chair into “a radio-controlled platform for mischief”. RC offers more range than wifi or bluetooth, and he was able to find a reasonably priced secondhand radio on Craigslist. However, he found out that in the event of signal loss, the receiver keeps sending the last commands to the speed controller. [zim] didn’t want his 150 lb (68kg) mischief platform getting loose, so he devised a fail-safe that cuts power to the motor when the signal is lost.

[zim] discovered that the receiver returns channel 3 (the throttle) to a preset condition whenever the signal is lost. He used a 24V HVAC relay controlled by an Arduino Nano to sample the PW on channel 3 and shut it off when either the throttle or the signal are cut.

If Grandma is feisty, you could build this caged-in version with a shopping cart.

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A Simple LED Flashlight Composed of a Relay and a Magnet

In our tips line we sometimes receive hacks that are amazing just because of their ingenuity. This relay-powered flashlight is definitely one of them. It has been named RattleGen by its creator [Berto], who apparently often makes simple hacks used in his everyday life (have a look at his YouTube channel).

To understand this hack, you first need to know (in case you didn’t already) that a magnet moving near a conductor (here a coil) induces a voltage at its terminals. This is called electromagnetic induction. In the picture you see above, you may distinguish a disassembled relay with a magnet located on the lever’s end. As a ferromagnetic metal is already placed inside the coil, the lever is by default ‘stuck’ in this position. By continuously pressing the latter on its other end, important voltage spikes are created at the coils terminals. [Berto] therefore used a bridge rectifier to transform the AC into DC, and a 1000uF capacitor to smooth the power sent to his super bright LED. A video of the system in action is embedded after the break.

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Recliner Sofa Given the Power of the Pi


If you go to buy a sofa these days you’ll not only be greeted with the option of one or more reclining positions, but a fully modern unit comes with motorized reclining. That simply wasn’t convenient enough for [Nicki] and [Kevin] who wanted to control the feature from a smartphone rather than a physical interface (buttons) on the side of the furniture. What resulted is the PiSofa, a Raspberry Pi connected to the furniture’s electronics with the help of a relay board.

This is most certainly a hack, but no doubt one with a lot of finesse. Check out that white PCB. That’s right, it’s a factory spun board to keep things nice and neat. They went with one of our favorite tricks by housing everything inside of a food storage container. After some Ruby coding the Pi now has complete control of the sofa. We’re not overstating this. It literally is the only way to control it because the original buttons no longer work. But that’s okay, turns out not only does it work with their smartphones, but with a [Kevin’s] Pebble watch as well.

We can’t think of any past hacks that specifically targeted the couch. But here’s a hammock that you can drive down the street.

Hackaday Links: December 8, 2013


Let’s start off with some high voltage. Here’s a sweet Jacob’s Ladder build from [Robert]. The site hosting his short writeup has been up and down for us so here’s a cache link.

Speaking of high voltage, if you want to switch mains with your project [Tom] has a breakout board for cheap mechanical relays. [via Dangerous Prototypes]

[Dario] made his own version of an electronic Advent calendar [translated]. There are no numbers, you must solve the mystery of the flashing LEDs to figure out which package goes with each day.

If you ever work with lighted arcade buttons here’s a guide for swapping out the light for an RGB LED. This hack uses through-hole LEDs. We’ve actually seen a surface mount hack that includes a PCB to mimic the old bulbs.

Next time you stay overnight at an event you can give yourself the best view in the campground. This tiny little camper was mounted on a scissor lift! That first step on the way to the Porta Potty is a doozy! [via Adafruit]

[Žiga] was nice enough to demonstrate this smart-watch hack by displaying our name and logo (we love pandering!). It features the MSP-WDS430 which is a surprisingly stylish offering from Texas Instruments. In addition to analog clock hands it has an OLED display driven by the MSP430 inside.

Here’s a quick PIC-based metal detector which [Nicholas] built.

And finally, [Chet] saw the oil tank level sensor we featured this week. He built a nearly identical system earlier this year. The oil level sensor works in conjunction with the custom thermostat he built around an Android tablet.