Mechanical 7-Segment Display Uses A Single Motor

June 27, 2021 by Danie Conradie 29 Comments

Seven-segment displays have been around for a long time, and there is a seemingly endless number of ways to build them. The latest of is a mechanical seven-segment from a master of 3D printed mechanisms, [gzumwalt], and can use a single motor to cycle through all ten possible numbers.

The trick lies in a synchronized pair of rotating discs, one for the top four segments and another for the bottom three segments. Each disc has a series of concentric cam slots to drive followers that flip the red segments in and out of view. The display can cycle through all ten states in a single rotation of the discs, so the cam paths are divided in 36° increments. [gzumwalt] has shown us a completed physical version, but judging by CAD design and working prototype of a single segment, we are pretty confident it will. While it’s not shown in the design, we suspect it will be driven by a stepper motors and synchronized with a belt or intermediate gear.

Another 3D printed mechanical display we’ve seen recently is a DIY flip dot, array, which uses the same electromagnet system as the commercial versions. [gzumwalt] has a gift for designing fascinating mechanical automatons around a single motor, including an edge avoiding robot and a magnetic fridge crawler.

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Mechanically Multiplexed Flip-Dot

June 24, 2021 by Danie Conradie 11 Comments

Flip dots displays are timeless classics, but driving the large ones can quickly turn into a major challenge. The electromagnets require a lot of current to operate, and the driver circuits can get quite expensive. [James Bruton] wanted to build his own, but followed a bit of a different route, building a mechanically multiplexed flip dot (ball?) display.

Each of the dots on [James]’ 5×3 proof of concept is a bistable mechanical mechanism that can either show or hide a ping pong ball sized half sphere. Instead of using electromagnets, the dots are flipped by a row of micro servos mounted on a moving carriage behind the display. The mechanism is derived from one of [James]’ previous projects, a mechanical multiplexer. Each dot mechanism has a hook at the back of the mechanism for a servo to push or pull to flip the dot. A major disadvantage of this design is the fact that the servo horn must match the state of the dot before moving through the hook, otherwise it can crash and break something, which also reduces the speed at which the carriage can move.

This build was just to get a feel for the concept, and [James] already has several ideas for changes and improvements. The hook design can certainly change, and a belt drive would really speed things up. We think this mechanical display is a very interesting design challenge, and we are interested to hear how our readers would tackle it? Let us know in the comments below.

Recently we covered a 3D printed flip dot display for the first time. It’s still small and [Larry Builds] is working out the kinks, but we would love to see it eventually match the mesmerising effect of Breakfast’s large installations.

Piezo Pickup Makes Wax Records Easy To Digitize

June 23, 2021 by Dan Maloney 27 Comments

Sound recording and playback have come a long way in the last century or so, but it’s fair to say there’s still a lot of interesting stuff locked away on old recordings. Not having a way to play it back is partly to blame; finding an antique phonograph that plays old-timey cylinder recordings is pretty hard. But even then, how do you digitize the output of these fragile, scratchy old recordings?

As it happens, [Jan Derogee] is in a position to answer these questions, with an antique phonograph and a bunch of Edison-style wax cylinders with voices and music from a bygone era locked away on them. It would be easy enough to just use the “reproducer” he previously built and set up a microphone to record the sound directly from the phonograph’s trumpet, but [Jan] decided to engineer a better solution. By adding the piezo element from an electronic greeting card to his reproducer, potted with liberal quantities of epoxy and padded with cotton, the piezo pickup was attached to the phonograph arm in place of the original stylus and trumpet. The signal from the piezo element was strong enough to require a shunt resistor, allowing it to be plugged directly into the audio input jack on a computer. From there it’s just an Audacity exercise, plus dealing with the occasional skipped groove.

We appreciate [Jan]’s effort to preserve these recordings, as well as the chance to hear some voices from the past. We’re actually surprised the recording sound as good as they do after all this time — they must have been well cared for.

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Even With AC, Hazmat Suit Isn’t Really Cool

June 21, 2021 by Al Williams 30 Comments

We’ll admit that the coolness factor of an air conditioned faux spacesuit made out of a hazmat suit will largely depend on where you wear it. At your next chess club meeting, maybe a hit. On a blind date, probably not. [Saveitforparts] apparently doesn’t mind and the combination of very warm weather and the donation of an expired hazmat suit, spurred his imagination as you can see in the video below.

A battery pack, a blower, and a box full of frozen water bottles completes the ensemble. Wireless temperature sensors show the outside temperature as well as temperature inside different parts of the suit. Does it work? We guess it must, but the roar of the fan is deafening and we have doubts about the frozen water cooling system. On the other hand, if you’re shooting a low budget science fiction thriller, this might be just the thing.

Even [Saveitforparts] admits this isn’t really practical and, as we suspected, he decided to get out of it as the condensing water started to run down his legs. Turns out astronauts and tank drivers use an undergarment made with small tubes of flowing water to stay cool.

This project reminded us of the positive pressure suit we saw a bit ago. Not to mention the one that went full body.

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Rock-A-Bye Baby, On The Mechatronic Crib Shaker

June 20, 2021 by Dan Maloney 13 Comments

While an engineering mindset is a valuable tool most of the time, there are some situations where it just seems to be a bad fit. Solving problems within the family unit would seem to be one such area, but then again, this self-rocking mechatronic crib seems to be just the cure for sleepytime woes.

From the look of [Peter]’s creation, this has less of a rocking motion and more of a gentle back-and-forth swaying. Its purpose is plainly evident to anyone who has ever had to rock a child to sleep: putting a little gentle motion into the mix can help settle down a restless infant pretty quickly. Keeping the right rhythm can be a problem, though, as can endurance when a particularly truculent toddler is fighting the urge to sleep. [Peter]’s solution is a frame of aluminum extrusion with some nice linear bearings oriented across the short axis of the crib, which sits atop the whole thing.

A recirculating ball lead screw — nothing but the best for [Junior] — and a stepper drive the crib back and forth. [Peter] took care to mechanically isolate the drivetrain from the bed, and with the selection of the drive electronics and power supply, to make sure that noise would be minimal. Although thinking about it, we’ve been lulled to sleep by the whining steppers of our 3D printer more than once. Or perhaps it was the fumes.

Hats off to [Peter] for a setup that’s sure to win back a little of the new parent’s most precious and elusive commodity: sleep.

Check Soil Moisture At A Glance With This Useful Display

June 18, 2021 by Lewin Day 6 Comments

Keeping soil moist is key to keeping most plants happy. It can be a pain having to dip one’s fingers into dirty soil on the regular, so it’s desirable to have a tool to do the job instead. [Andrew Lamchenko] built a capable soil moisture monitor, and equipped it with an E-ink display for easy readings at a glance.

The device is built around the NRF52810 or other related NRF52 microcontrollers, which run the show. Rather than using an off-the-shelf sensor to determine soil conditions, an LMC555CMX timer chip is used, a variant of the classic 555 timer designed for low power consumption. Combined with the right PCB design, this can act as a moisture sensor by detecting capacitance changes in the soil. The sensor is also able to send data using the MySensor protocol, allowing it to be used as a part of a home automation system.

The soil is tested periodically with the moisture sensor, and displayed on the attached e-ink screen. Since the e-ink display requires no electricity except when rewriting the display, this allows the sensor to operate for long periods without using a lot of battery power. The soil can be checked, the display updated, and then the entire system can be put to sleep, using tiny amounts of power until it’s time to test the soil again.

It’s a great example of design for low power applications, where component selection really is everything. We’ve featured [Andrew]’s projects before; he’s long been a fan of using e-ink displays to create long-lasting, low power budget sensor platforms. Video after the break.

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Blowing A 5000 A Fuse Takes Some Doing

June 18, 2021 by Lewin Day 37 Comments

Fuses are generally there to stop excessive electrical currents from damaging equipment or people’s soft, fleshy bodies when faults occur. However, some people like to blow them just for fun, and [Photonicinduction] is just one of those people. He recently decided to push the boat out, setting his mind to the task of popping a 5000 A fuse in his own back yard. (Video, embedded below.)

The fuse looks quite haggard after the event

It’s not a job for the faint-hearted. The fuse is rated at 5,000 A — that’s the nominal rating for the currents at which it is intended to operate. Based on the datasheet, the part in question is capable of withstanding 30,000 A for up to five full seconds. To pop the fuse instantly takes something in the realm of 200,000 A.

To achieve this mighty current, a capacitor bank was built to dump a huge amount of energy through the fuse. Built out of ten individual capacitor units wired up in parallel, the total bank comes in at 10,000 μF, and is capable of delivering 200,000 A at 3000 V. (Just not for very long.) The bank was switched into circuit with the fuse via a pneumatic switch rated at just 12,000 A.

The results are ferocious, with both the fuse and switch contacts blasting out hot metal and flashes of light when the power is dumped. It’s a heck of a display. We’ve featured big capacitor banks before too, though they pale in comparison to what we’ve seen here today.

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