solenoid

140 Articles

Internals of ding-dong doorbell.

Wireless Doorbell Extension Features Home-Wound Coil

May 16, 2025 by 12 Comments

Today in the it’s-surprising-that-it-works department we have a ding dong doorbell extension from [Ajoy Raman].

What [Ajoy] wanted to do was to extend the range of his existing doorbell so that he could hear it in his workshop. His plan of attack was to buy a new wireless doorbell and then interface its transmitter with his existing doorbell. But his approach is something others might not have considered if they had have been tasked with this job, and it’s surprising to learn that it works!

What he’s done is wrap a new coil around the ding dong doorbell’s solenoid. When the solenoid activates, a small voltage is induced into the coil. This then gets run into the wireless doorbell transmitter power supply (instead of its battery) via a rectifier diode and a filter capacitor. The wireless doorbell transmitter — having also had its push-button shorted out — operates for long enough from this induced electrical pulse to transmit the signal to the receiver. To be clear: the wireless transmitter is fully powered by the pulse from the coil around the solenoid. Brilliant! Nice hack!

We weren’t sure how reliable the transmitter would be when taken out of the lab and installed in the house so we checked in with [Ajoy] to find out. It’s in production now and operating well at a distance of around 50 feet!

Of course we’ve published heaps of doorbell hacks here on Hackaday before, such as this Bluetooth Low Energy (BLE) doorbell and this light-flashing doorbell. Have you hacked your own doorbell? Let us know on the tips line!

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Dozens Of Solenoids Turn Vintage Typewriter Into A Printer

April 8, 2025 by 16 Comments

An electric typewriter is a rare and wonderful thrift store find, and even better if it still works. Unfortunately, there’s not as much use for these electromechanical beauties, so if you find one, why not follow [Konstantin Schauwecker]’s lead and turn it into a printer?

The portable typewriter [Konstantin] found, a Silver Reed 2200 CR, looks like a model from the early 1980s, just before PCs and word processing software would sound the death knell for typewriters. This machine has short-throw mechanical keys, meaning that a physical press of each key would be needed rather than electrically shorting contacts. Cue the order for 50 low-voltage solenoids, which are arranged in rows using 3D printed holders and aluminum brackets, which serve as heat sinks to keep the coils cool. The solenoids are organized into a matrix with MOSFET drivers for the rows and columns, with snubber diodes to prevent voltage spikes across the coils, of course. A Raspberry Pi takes care of translating an input PDF file into text and sending the right combination of GPIO signals to press each key.

The action of the space bar is a little unreliable, so page formatting can be a bit off, but other than that, the results are pretty good. [Konstantin] even managed to hook the printer up to his typewriter keyboard, which is pretty cool, too.

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Piano Gets An Arduino Implant

February 16, 2025 by 18 Comments

[Paul] likes his piano, but he doesn’t know how to play it. The obvious answer: program an Arduino to do it. Some aluminum extrusion and solenoids later, and it was working. Well, perhaps not quite that easy — making music on a piano is more than just pushing the keys. You have to push multiple keys together and control the power behind each strike to make the music sound natural.

The project is massive since he chose to put solenoids over each key. Honestly, we might have been tempted to model ten fingers and move the solenoids around in two groups of five. True, the way it is, it can play things that would not be humanly possible, but ten solenoids, ten drivers, and two motors might have been a little easier and cheaper.

The results, however, speak for themselves. He did have one problem with the first play, though. The solenoids have a noticeable click when they actuate. The answer turned out to be orthodontic rubber bands installed on the solenoids. We aren’t sure we would have thought of that.

Player pianos, of course, are nothing new. And, yes, you can even make one with a 555. If a piano isn’t your thing, maybe try a xylophone instead.

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Cool Kinetic Sculpture Has Tooling Secrets To Share

January 29, 2025 by 8 Comments

Occasionally, we get a tip for a project that is so compelling that we just have to write it up despite lacking details on how and why it was built. Alternatively, there are other projects where the finished product is cool, but the tooling or methods used to get there are the real treat. “Homeokinesis,” a kinetic art installation by [Ricardo Weissenberg], ticks off both those boxes in a big way.

First, the project itself. Judging by the brief video clip in the reddit post below, Homeokinesis is a wall-mounted array of electromagnetically actuated cards. The cards are hinged so that solenoids behind them flip the card out a bit, making interesting patterns of shadow and light, along with a subtle and pleasing clicking sound. The mechanism appears to be largely custom-made, with ample use of 3D printed parts to make the frame and the armatures for each unit of the panel.

Now for the fun part. Rather than relying on commercial solenoids, [Ricardo] decided to roll his own, and built a really cool CNC machine to do it. The machine has a spindle that can hold at least eleven coil forms, which appear to be 3D printed. Blank coil forms have a pair of DuPont-style terminal pins pressed into them before mounting on the spindle, a job facilitated by another custom tool that we’d love more details on. Once the spindle is loaded up with forms, magnet wire feeds through a small mandrel mounted on a motorized carriage and wraps around one terminal pin by a combination of carriage and spindle movements. The spindle then neatly wraps the wire on the form before making the connection to the other terminal and moving on to the next form.

The coil winder is brilliant to watch in action — however briefly — in the video below. We’ve reached out to [Ricardo] for more information, which we’ll be sure to pass along. For now, there are a lot of great ideas here, both on the fabrication side and with the art piece itself, and we tip our hats to [Ricardo] for sharing this.

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How Crane Games Are Playing Claw Games With The Player

January 4, 2025 by 42 Comments

Fresh from AliExpress, [Big Clive] got another fascinating item to tear down: a crane claw, as used in those all too familiar carnival games. These games feature a claw the player moves into position above a pile of toys or other items. Lower the claw gently down in the hopes that it grabs the target item. In a perfect world, the claw will move your prize and deposit it, via a chute, into your waiting hands. Of course, everyone knows that these games are rigged and rely less on skill or luck than the way that they are programmed, but the way that this works is quite subtle, as you can see in the video below.

Despite how complex these crane claws may appear, they are simply solenoids, with the metal rod inside providing the claw action. The weight of the rod and claw section opens the claw via gravity. The strength of the claw is thus fully dependent on how strongly the solenoid is being driven, which, as [Clive] demonstrates, depends on the voltage and the duty cycle. At only 12V, the target plushie will easily slip away again as the claw barely has any strength, while at 24V, it’s pretty solid.

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Player Ukulele Pulls Your Strings

September 13, 2024 by 6 Comments

Automated musical instruments aren’t a new idea. From water chimes to player pianos, they’ve been around for a while. But we can’t remember the last time we saw a player ukulele. [Zeroshot] shows us one, though, and it uses an Arduino. You can see and hear it in the video below.

Honestly, with all the stepper motors, linear rails, and belts, we thought it looked like a 3D printer, at least up at the business end. [Zeroshot] thought it would be easier to build a robot than to actually learn to play the instrument. We aren’t sure we agree.

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Custom Pneumatic Cylinders Lock This Monitor Arm In Place

August 9, 2024 by 8 Comments

Few consumer-grade PCs are what you’d categorize as built to last. Most office-grade machines are as likely as not to give up the ghost after ingesting a few too many dust bunnies, and the average laptop can barely handle a few drops of latte and some muffin crumbs before croaking. Sticking a machine like that in the shop, especially a metal shop, is pretty much a death sentence.

And yet, computers are so useful in the shop that [Lucas] from “Cranktown City” built this neat industrial-strength monitor arm. His design will look familiar to anyone with a swing-arm mic or desk light, although his home-brew parallelogram arm is far sturdier thanks to the weight of the monitor and sheet-metal enclosure it supports. All that weight exceeded the ability of the springs [Lucas] had on hand, which led to the most interesting aspect of the build — a pair of pneumatic locks. These were turned from a scrap of aluminum rod and an old flange-head bolt; when air pressure is applied, the bolt is drawn into the cylinder, which locks the arm in place. To make it easy to unlock the arm, a pneumatic solenoid releases the pressure on the system at the touch of a button. The video below has a full explanation and demonstration.

While we love the idea, there are a few potential problems with the design. The first is that this isn’t a fail-safe design, since pressure is needed to keep the arm locked. That means if the air pressure drops the arm could unlock, letting gravity do a number on your nice monitor. Second is the more serious problem [Lucas] alluded to when he mentioned not wanting to be in the line of fire of those locks should something fail and the piston comes flying out under pressure. That could be fixed with a slight design change to retain the piston in the event of a catastrophic failure.

Problems aside, this was a great build, and we always love [Lucas]’ seat-of-the-pants engineering and his obvious gift for fabrication, of which his wall-mount plasma cutter is a perfect example.

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