Hackaday Podcast 040: 3D Printed Everything, Strength V Toughness, Blades Of Fiber, And What Can’t Coffee Do?

Hackaday Editors Mike Szczys and Elliot Williams opine on the coolest hacks we saw this week. This episode is heavy with 3D printing as Prusa released a new, smaller printer, printed gearboxes continue to impress us with their power and design, hoverboards are turned into tanks, and researchers suggest you pour used coffee grounds into your prints. Don’t throw out those “toy” computers, they may be hiding vintage processors. And we have a pair of fantastic articles that cover the rise and fall of forest fire watchtowers, and raise the question of where all those wind turbine blades will go when we’re done with them.

Take a look at the links below if you want to follow along, and as always tell us what you think about this episode in the comments!

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Not All 7-Segment Displays Are Electronic

There are a variety of means by which numbers can be displayed from an electronic circuit, and probably the most ubiquitous remains the seven-segment display. Take seven LEDs, lamps, LCDs, VFD segments or mechanical flip-dot style units in the familiar rectangular figure eight, and your microcontroller or similar can display numbers. There are a variety of different interfaces, but at most all that is needed is a level shifter and a driver.

Sometimes though we encounter a completely novel 7-segment display, and such is the case with [Fhuable]’s all mechanical single digit display. It bears a superficial resemblance to a flipdot display, but instead of a magnetic actuator, it instead uses a complex system of gears and cams to flip the segments sequentially from the turning of a small crank. It appears to be the same mechanism he’s used in his subscription counter project whose video we’ve placed below the break, and it is truly a thing of beauty. We’re not entirely certain how useful it would be as a general-purpose display in its current form, however, we can see it being adapted with relative ease. A clock might, for example, be an eye-catching project.

Most displays that make it here have some electrical components, so it’s unusual to see an entirely mechanical one. But that’s not necessarily always the case.

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Measure Your YouTube Importance

How do you hack your motivation? Do you put red marker Xs on a paper calendar every day you exercise? Do you use an egg timer to sprint through dozens of emails? Do you lock all the doors and shut off your data to write some bulletproof code? If you are [Hulk], you build a YouTube Desktop Notifier showing his YouTube subscribers and views. This is his ticket to getting off the couch to make a video about just such a device. There is something poetic about building a mechanism to monitor its own success making a feedback loop of sorts. The Hackaday.io page follows the video, so anyone who wants to build their own doesn’t have to scribble notes while pausing the video which is also posted below the break.

The hardware list is logical, starting with a NodeMCU module programmed through the Arduino IDE. Addressable 7-segment displays show the statistics in red, but you can sub in your preferred color with the back-lighting LEDs. It should be possible to share the CLK pins on the displays if you are important enough to need more digits. [Hulk] already outlined a list of improvements including switching to addressable backlights and adding daily and monthly tracking.

Monitoring online values without a computer monitor is satisfying on a level because it shows what motivates us, whether that is Bitcoin or the weather.

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Tiny Two-Digit Thermometer Has Long Battery Life

Like most of his work, this tiny two-digit thermometer shows that [David Johnson-Davies] has a knack for projects that make efficient use of hardware. No pin is left unused between the DS18B20 temperature sensor, the surface mount seven-segment LED displays, and the ATtiny84 driving it all. With the temperature flashing every 24 seconds and the unit spending the rest of the time in a deep sleep, a good CR2032 coin cell should power the device for nearly a year. The board itself measures only about an inch square.

You may think that a display that flashes only once every 24 seconds might be difficult to actually read in practice, and you’d be right. [David] found that it was indeed impractical to watch the display, waiting an unknown amount of time to read some briefly-flashed surprise numbers. To solve this problem, the decimal points flash shortly before the temperature appears. This countdown alerts the viewer to an incoming display, at the cost of a virtually negligible increase to the current consumption.

[David]’s project write-up explains how everything functions. He also steps through the different parts of the source code to explain how everything works, including the low power mode. The GitHub repository holds all the source files, and the board can also be ordered direct from OSH Park via their handy shared projects feature.

Low power consumption adds complexity to projects, but the payoffs can easily be worth the time spent implementing them. We covered a detailed look into low power WiFi microcontrollers that is still relevant, and projects like this weather station demonstrate practical low power design work.

7-Segment Display Is 3D Printed And Hand Cranked

[Peter Lehnér] has designed a brilliant 7-segment flip-segment display that doesn’t really flip. In fact, it doesn’t use electromagnets at all. This one is 3D printed and hand cranked. It’s a clever use of a cam system to set the segments for each digit (0-9) makes it a perfect entry in the Hackaday 3D Printed Gears, Pulleys, and Cams contest.

We find the nomenclature of these displays to be a bit confusing so let’s do a quick rundown. You may be most familiar with flip-dot displays, basically a dot-matrix grid of physical pixels that are black on one side and brightly colored (usually chartreuse) on the other. We saw a giant flip-dot display at CES four years ago. Akin to flip-dots are flip-segment displays which do the same thing but with segments of a digit rather than dots. We featured a 3D printed version of these last week. The common aspect of most flip displays is an electromagnet used to change the state of the dot or segment.

The version [Peter] designed gets rid of the magnets and coils, replacing them with mechanical logic instead. Each segment sits in a track on the frame of the digit. When slid to one position it is hidden by the bezel, in the other position it slides into view. A cleverly designed set of cams move the segments at each of 10 positions. The animated graphic here shows three cams which are responsible for moving just two of the segments. More cams are added to complete assembly, a process shown in the second half of the demo video found below.

We’re delighted to see this as an entry in the contest and can’t wait to see what kind of gear, cam, or pully scheme is built into your projects!

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Hot Glue Makes These Segments Glow

It’s safe to say that hot-melt glue is a staple of the projects we see here at Hackaday. There won’t be many readers who don’t have a glue gun, and a blob of the sticky stuff will secure many a project. But it’s not so often we see it used as an integral component for a property other than its stickiness, so [DusteD]’s reaction timer project is interesting for having hot glue as a translucent light guide and diffuser for its LED seven-segment display.

The timer is simple enough, being driven by an Arduino board, while the display is pre-formed into the 3D-printed case. The hot glue fills the enclosures behind each segment, and after several experiments it was found that the best filling method was from behind against a piece of Kapton tape. The LEDs were wired into a common cathode array, and along with the arcade-style button and the Arduino the whole fitted neatly in the box. You can see the result in action in the video below the break.

Of course, this display is unusual for its use of hot glue, but not unique. We’ve seen a different take on a hot glue light pipe display before.

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Electromagnetic 7-Segment Display Easy On The Eyes AND The Ears

We love electromagnetic displays: take the modern look of a digital readout, combine with the low-tech coil mechanism that you theoretically could create yourself, add a dash of random clacking sounds, and what’s not to like? Evidently, [Nicolas Kruse] shares our affection for these displays, because he’s taken it beyond theory and created a 7-segment magnetically-actuated display from scratch.

The display is 3D-printed, as you would expect these days. Each segment contains a small neodymium magnet, and each coil a 1 mm iron core for flux concentration. The coils are driven with a 1.6 A peak current, causing the segments to flip in less than 10 ms. [Nicolas] provides STL files for the display base, segments, and spools so you can print your own display. He’s also released the schematics and code for the driver, which uses an ATtiny44 to drive the coils through N- and P-channel MOSFETs. Initially designed to drive a passive 4×7 matrix of displays, the driver couldn’t quite manage to flip one segment without affecting its neighbors. However, for a single display, the driver works fine. We hope he figures out the matrix issue soon, because we really want to see a clock made with these displays.

You can see (and hear) a short video of the display in action after the break. The clacking does not disappoint!

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