A Lawnmower That Looks Where You’re Going

October 15, 2020 by Matthew Carlson 21 Comments

As a kid, one of the stories my dad told me was about mowing a fairly large field of grass on the farm with a gas-powered push mower. One day, some sort of farm tool was left in the field and the old industrial mower shredded it, sending a large piece of sharp metal hurtling toward his leg. Luckily for my dad, the large plastic wheel managed to stop the piece of metal, destroying the wheel. My grandfather was frustrated that he needed to repair the lawnmower but was grateful that my dad still had both feet attached.

Of course, this story was used as a lesson for me not to gripe about having to mow the lawn when it was my turn, but there was also the lesson that lawnmowers can be dangerous. [DuctTape Mechanic] took it upon himself to see if he could prevent that sort of accident altogether and has created an automatic safety shutdown mechanism for his family lawnmower. (Video embedded below.)

This uses an inductive sensor that can detect metal before it gets sucked into the mower itself. The sensor trips a relay which forcibly shuts the mower down by grounding the ignition coil. While it doesn’t physically stop the blade like other safety mechanisms, it does prevent a situation from escalating by turning off power to the blade as soon as possible. Getting to the ignition coil wasn’t easy as it required getting deep into the engine itself, but now [DuctTape Mechanic] has a mower that could be expanded further with things such as with a capacitive sensor or more smarts to determine if it is detecting underground or above ground metal.

Someday we’ll have robotic mowers, but until then, we laud the efforts of hackers out there trying to make the world a little safer.

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Air Cannon Serves Up A Blast Of Ferrocerium Sparks

October 15, 2020 by Dan Maloney 25 Comments

OK, looks like we have a new way to entertain the kids and wreak havoc in the neighborhood, if this spark-shooting ferrocerium cannon is as easy to build as it looks.

This one comes to us by well-known purveyor of eyebrow-singing projects [NightHawkInLight], whose propane torch never seems to get a break. The idea here is a large scale version of an apparently popular trick where the “flints” from lighters, which are actually rods of ferrocerium, an aptly named alloy of iron and cerium, are heated to a nearly molten state and dropped onto a hard surface. The molten alloy thence explodes in a shower of sparks, to the mirth and merriment of those in attendance.

[NightHawkInLight]’s version of the trick scales everything up. Rather than lighter flints, he uses ferrocerium rods from firestarters of the type used for camping. The rod is stuffed into a barrel formed from steel brake line which is connected to the output of a PVC air chamber. His ominpresent propane torch is attached in such a way as the flame plays upon the loaded pyrophoric plug, heating it to a molten state before the air is released from the chamber. The massive display of sparks seen in the video below is pretty impressive, but we’re getting tired of gender reveal parties and forest fires. We just hope he had fire extinguishers on hand.

Seriously, be careful with stuff like this. [NightHawkInLight] has a lot of experience working with these kinds of projects, from his plasma-propelled soda bottles to making synthetic rubies with an arc welder. We’re sure he wouldn’t want to see anyone get hurt.

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Homebrew Pulsejet Uses Carbon Fiber To Great Effect

October 14, 2020 by Zoe Skyforest 21 Comments

Jet engines are undeniably awesome, but their inherent complexity prevents many from experimenting with the technology at home. Perhaps the most accessible design is the pulsejet; in valveless form, it can be built relatively easily without needing a lot of precision spinning parts. [Integza] decided to try building his own, facing many hurdles along the way. (Video, embedded below.)

Despite eschewing turbines and compressors, and consisting of just an intake, exhaust and a combustion chamber, the pulsejet still presents many challenges to the home gamer. Primary concerns are sustaining combustion without the jet flaming out, and building the jet out of suitable materials that won’t simply melt into a gooey puddle on the floor.

[Integza]’s design process began with many 3D-printed attempts. While the geometry was on point, none of these designs could run for more than a few seconds without melting and falling apart. Determined to avoid the typical welded-steel approach, [Integza] instead resolved to go left-of-field with carbon fibre mat combined with high-temperature sealant. With the help of a 3D-printed mold, he was able to produce a working engine that could stand up to the high temperatures and produce that glorious pulsejet sound.

It’s come a long way from [Integza]’s earlier experiments, and we look forward to seeing where it goes next – whether that be on a plane or perhaps even a go-kart. Video after the break.

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Making A Servo Tester Just A Bit Better

October 13, 2020 by Zoe Skyforest 9 Comments

Servo testers are useful devices to have on hand, allowing one to quickly check a given part for proper operation. However, cheaper models can be quite limited, and may not output signals suitable for testing the full range of servos out there. [Buttim] had a few testers laying around, and wanted to see if they could be modified to do more.

Initial experiments with the cheapest model on hand came to naught, revealing nothing but a small IC with its markings scrubbed off. However, going a few more dollars upmarket, [buttim] found a servo tester packing a Nuvoton N75E003. An unfamiliar name to the hobbyist, Nuvoton microcontrollers are often found in mass-production designs due to their low cost.

The N75E003 is a 8051-based device, and [buttim] was able to source a programmer and tutorial resources on how to work with the chip. Armed with the right hardware and knowledge, the servo tester was first programmed with a basic blink sketch. With everything confirmed to be working as expected, [buttim] set about programming a custom firmware for the servo tester that would output a broader range of PWM signals to suit their needs.

It’s a great example of the learning possibilities available by simply cracking open the case of commodity hardware and diving in. Of course, if you need something even more capable, you can always build your own from scratch!

DIY Braille Embosser Is Really Impressive

October 10, 2020 by Kristina Panos 21 Comments

We weren’t surprised to learn that Braille tools are quite expensive. But it’s interesting to hear that there’s another class of tools altogether, and they are very cheap and imprecise. In devising the Braille Embossing Experience, aka BEE, [alatorre] sought to find an open-source middle ground. We think they succeeded marvelously.

Another surprising thing — while handheld embossers do exist, there is no system for filling out an A4 sheet of paper, say, to write a letter.

For Braille to be readable, the characters and lines must be properly spaced, and this requires some kind of moveable type-like device to correctly register the characters onto paper. BEE fills this void as well. The amazing thing is, there’s not much more to it than a marked-up piece of aluminum and some clever 3D printing.

There are two parts to this system — the positioning rail, which includes a landing box for the embosser with six holes in the bottom. The other part is a pair of embossers, one for letters A-M, and another for letters N-Z. To use BEE, just slide the rail to the right and start embossing letters right to left, then flip the paper over when finished.

Need to create something more permanent? Make a Braille PCB.

Fat Bottomed-Keebs, You Make The Clackin’ World Go Round

October 9, 2020 by Kristina Panos 24 Comments

Depending on the circles you run in, it can seem like the mechanical keyboard community is all about reduced layouts, and keebs without ten-keys are about as big as it gets. But trust us, there’s plenty of love out there for the bigger ‘boards like [Ben]’s tasty fat-bottomed keyboard. Man oh man, what a delicious slab of throwback to the days when keyboards doubled as melee weapons.

More specifically, this is a 199-key modified Sun Type 5 layout. It runs on two Teensy 2.0s — one for the keyboard matrix, and one for everything else. [Ben] made the metal enclosure entirely by hand without a CNC or laser cutter. While I don’t personally care for linear switches, I have mad respect for these, which are vintage Cherry Blacks pulled from various 1980s AT/XT boards. That 10-key island on the left is dedicated to elementary macros like undo/redo, cut/copy/paste, and open/close/save.

We absolutely love the gigantic rotary encoders, which give it a bit of a boombox look. There’s even reuse involved here, because the encoder knobs are made from jam jar lids that are stuffed with homemade Sugru. [Ben] can use them to play PONG on the LCD and other games not yet implemented on the everything-else Teensy.

Here’s another Sun-inspired keeb, but this one has a reverse 10-key layout that matches the DTMF phone dial.

Tiny Trash Can Repels Trash Pandas, Medium-Sized Cats

October 9, 2020 by Kristina Panos 16 Comments

Are you tired of cats and other wildlife relieving themselves in your outdoor plant pots? As if accidental neglect won’t kill them fast enough. [TecnoProfesor] has a solution, and it doesn’t even involve a microcontroller. It detects the presence of approaching animals and then blasts them with annoying sounds and a couple of bright green LEDs to drive them away.

Thanks to a couple of modules, the circuit is really pretty simple. There’s a PIR to detect the animals, a buzzer, and a 555-based pulse generator to play tones through the buzzer. This circuit can run 24/7 on a pair of 6V solar panels that charge up a battery. We particularly like the desk trash can enclosure, though we have to wonder how waterproof this system is. Check out the brief demo after the break.

For all of you satisfied with the 555 implementation here, your reward is this giant functioning 555. If you’re a 555 naysayer, how would you have done it better?

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