Mechanical Seven-Segment Display Really Sticks Out From The Pack

July 27, 2020 by Dan Maloney 20 Comments

We’ve been displaying numbers using segmented displays for almost 120 years now, an invention that predates the LEDs that usually power the ubiquitous devices by a half-dozen decades or so. But LEDs are far from the only way to run a seven-segment display — check out this mechanical seven-segment display for proof of that.

We’ve been seeing a lot of mechanical seven-segment displays lately, and when we first spotted [indoorgeek]’s build, we thought it would be a variation on the common “flip-dot” mechanism. But this one is different; to form each numeral, the necessary segments protrude from the face of the display slightly. Everything is 3D-printed from white filament, yielding a clean look when the retracted but casting a sharp shadow when extended. Each segment carries a small magnet on the back which snuggles up against the steel core of a custom-wound electromagnet, which repels the magnet when energized and extends the segment. We thought for sure it would be loud, but the video below shows that it’s really quiet.

While we like the subtle contrast of the display, it might not be enough for some users, especially where side-lighting is impractical. In that case, they might want to look at this earlier similar display and try contrasting colors on the sides of each segment.

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Experimenting With Vibratory Wind Generators

June 30, 2020 by Tom Nardi 42 Comments

We’ve all got a pretty good mental image of the traditional wind-powered generator: essentially a big propeller on a stick. Some might also be familiar with vertical wind turbines, which can operate no matter which way the wind is blowing. In either case, they use some form of rotating structure to harness the wind’s energy.

But as demonstrated by [Robert Murray-Smith], it’s possible to generate electrical power from wind without any moving parts. With simple components, he shows how you can build a device capable of harnessing the wind with nothing more than vibrations. Alright, so we suppose that means the parts are technically moving, but you get the idea.

In the video after the break, [Robert] shows two different devices that operate under the same basic principle. For the first, he cuts the cone out of a standard speaker and glues a flat stick to the voice coil. As the stick moves back and forth in the wind, the coil inside of the magnet’s field and produces a measurable voltage. This proves the idea has merit and can be thrown together easily, but isn’t terribly elegant.

For the revised version, he glues a coil to a small piece of neoprene rubber, which in turn is glued to a slat taken from a Venetian blind. On the opposite side of the coil, he glues a magnet. When the blind slat starts vibrating in the wind, the oscillation of the magnet relative to the coil is enough to produce a current. It’s tiny, of course. But if you had hundreds or even thousands of these electric “blades of grass”, you could potentially build up quite a bit of energy.

If this all sounds a bit too theoretical for your tastes, you can always 3D print yourself a more traditional wind turbine. We’ve even seen them in vertical form, if you want to get fancy.

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Flipdots, Without The Electronics

June 13, 2020 by Jenny List 14 Comments

We are used to flipdots, single mechanical pixels that are brightly colored on one side and black on the other, flipped over by a magnetic field. Driving the little electromagnets that make them work is a regular challenge in our community. [Johan] however has a new take on the flipdot, and it’s one we’ve never seen before. Instead of making a magnetic field to flip his dots he’s doing without the electronics entirely, and just using a magnet.

The project is a level indicator for a water tank, which contains a magnet floating in a plastic bottle. This has previously been used to trigger a reed switch that controls the refill pump. To those reed switches he adds a row of flipdots, but these aren’t the commercial dots you might once have seen adorning the front of your local bus. Instead, they’re custom dots made from washers, suspended in pivots by means of a spot weld and mounted in a frame inside a clear tube to keep dirt at bay. As you can see in the video below the break, when the magnet floats past inside the tank it flips them over one way, and on its return journey if flips them back the other. The result is a fully serviceable flipdot display, completely lacking the normal electronics, and we rather like it.

(It may be the first electronic-free flipdot we’ve shown you, but it’s not the first homemade one.)

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Simple Demo Shows The Potential Of Magnetic Gears

April 13, 2020 by Dan Maloney 27 Comments

We’ve probably all used gears in our projects at one time or another, and even if we’re not familiar with the engineering details, the principles of transmitting torque through meshed teeth are pretty easy to understand. Magnetic gears, though, are a little less intuitive, which is why we appreciated stumbling upon this magnetic gear drivetrain demonstration project.

[William Fraser]’s demo may be simple, but it’s a great introduction to magnetic gearing. The stator is a block of wood with twelve bolts to act as pole pieces, closely spaced in a circle around a shaft. Both ends of the shaft have rotors, one with eleven pairs of neodymium magnets arranged in a circle with alternating polarity, and a pinion on the other side of the stator with a single pair of magnets. When the pinion is spun, the magnetic flux across the pole pieces forces the rotor to revolve in the opposite direction at a 12:1 ratio.

Watching the video below, it would be easy to assume such an arrangement would only work for low torque applications, but [William] demonstrated that the system could take a significant load before clutching out. That could even be a feature for some applications. We’ve got an “Ask Hackaday” article on magnetic gears if you want to dive a little deeper and see what these interesting mechanisms are good for.

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Fail Of The Week: How Not To Die Of Boredom During Isolation

April 1, 2020 by Dan Maloney 26 Comments

They say you can’t actually die from boredom, but put a billion or so people into self-isolation, and someone is bound to say, “Hold my beer and watch this.” [Daniel Reardon]’s brush with failure, in the form of getting magnets stuck up his nose while trying to invent a facial touch reminder, probably wasn’t directly life-threatening, but it does underscore the need to be especially careful these days.

The story begins with good intentions and a small stack of neodymium magnets. [Daniel]’s idea for a sensor to warn one of impending face touches was solid: a necklace with magnetic sensors and wristbands studded with magnets. Sounds reasonable enough; one can easily see a compact system that sounds an alarm when a hand subconsciously crosses into the Danger Zone while going in for a scratch. Lacking any experience in circuits, though, [Daniel] was unable to get the thing working, so he started playing with the magnets instead. One thing led to another, and magnets were soon adorning his earlobes, and then his nostrils. Unfortunately, two magnets became locked on either side of his septum, as did two others meant to neutralize the pull of the first pair. So off [Daniel] went to the emergency department for a magnetectomy.

Of course it’s easy to laugh at someone’s misfortune, especially when self-inflicted. And the now-degaussed [Daniel] seems to be a good sport about the whole thing. But the important thing here is that we all do dumb things, and hackers need to be especially careful these days. We often work with sharp, pointy, sparky, toxic, or flammable things, and if we don’t keep our wits about us, we could easily end up in an ER somewhere. Not only does that risk unnecessary exposure to COVID-19, but it also takes medical resources away from people who need it more than you do.

By all means, we should be hacking away these idle hours. Even if it’s not in support of COVID-19 solutions, continuing to do what we do is key to our mental health and well-being. But we also need to be careful, to not stretch dangerously beyond our abilities, and to remember that the safety net that’s normally there to catch us is full of holes now.

Thanks to [gir.st] for the tip — you actually were the only one to send this in.

Inverse Kinematics Robot Arm Magna-Doodles The Time For You

March 24, 2020 by Erin Pinheiro 8 Comments

Following a surge of creativity fueled by the current lockdown, [Diglo] writes in with his tabletop clock driven by a robotic arm drawing on a Magna Doodle tablet. And if you have one of those still lying around with some old toys and don’t mind cannibalizing it for the project, you too can follow along the source files to build your own.

The clock works by exploiting the principle that Magna Doodle tablets work by being drawn on with a magnetic stylus. That way, to draw on one of them you don’t need to add a point of articulation to bring the pen up and down, [Diglo] simply attached a controllable electromagnet to the end of a two-dimensional SCARA arm. In total, the whole build uses three stepper motors, two to control the movement of the arm, and one on the back of the tablet to sweep a magnetic bar which “erases” it.

This clock is similar to another we’ve featured a few years ago, which also used a Magna Doodle, but greatly improves on the idea. If a Magna Doodle seems too childish to build a magnetic clock however, there’s always ferrofluidic displays to try to dip your fingers into, but we really think you should watch this one in action after the break first.

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A Tin Can Phone, But With Magnets

February 29, 2020 by Brian McEvoy 17 Comments

The tin can phone is a staple of longitudinal wave demonstrations wherein a human voice vibrates the bottom of a soup can, and compression waves travel along a string to reproduce the speaker in another can at the other end. All the parts in this electrical demonstration are different, but the concept is the same.

Speakers are sound transducers that turn electrical impulses into air vibrations, but they generate electricity when their coil vibrates. Copper wires carry those impulses from one cup to another. We haven’t heard of anyone making a tin can phone amplifier, but the strictly passive route wasn’t working, so an op-amp does some messy boosting. The link and video demonstrate the parts and purposes inside these sound transducers in an approachable way. Each component is constructed in sequence so you can understand what is happening and make sense of the results.

Can someone make a tin can ~~amplifier~~ transformer? We’d like to see that. In another twist of dual-purpose electronics, did you know that LEDs can sense light?

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