How TTY Opened Up The Phones For The Hard Of Hearing

April 30, 2026 by Zoe Skyforest 16 Comments

The telephone was an invention that revolutionized human communication. No more did you have to physically courier a letter from one place to another, or send a telegram, or have a runner carry the message for you. Instead, you could have a direct conversation with another person a great distance away. All well and good if you can speak and hear, of course, but rather useless if you happen to be deaf.

Those hard of hearing were not left entirely out of the communication revolution, however. Well before IP switched networks and the Internet became a thing, there was already a way for the deaf to communicate over the plain old telephone network—thanks to the teletypewriter!

Over The Wires

The teletypewriter (TTY) has been around for a long time. The first device came into being in 1964, developed by James C. Marsters and Robert Weitbrecht, both deaf. Their idea was to create a method for deaf individuals to communicate over the phone network in a textual manner. To this end, the group sourced teleprinters formerly used by the US Department of Defense, and hooked them up with acoustic couplers that would allow them to mate with the then-ubiquitous AT&T Model 500 telephone. Thus, the TTY was born. A user could dial another TTY machine, and key in a message, which would print out at the other end. The receiving user could then respond in turn in the same manner.

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Bicycle Tubes Aren’t Just Made Of Rubber Anymore

April 29, 2026 by Zoe Skyforest 47 Comments

For the average rider, inner tubes have been one of the most enduring and unchanging parts of bicycle design over the decades. They’re made of rubber, they have a Schrader or Presta valve, and they generally do an okay job at cushioning the ride.

However, if you’re an above-average rider, or just obsessive about your gear, you might consider butyl rubber tubes rather old hat. Today, there are far fancier—and more expensive—options on the market if you’re looking to squeeze every drip of performance out of your bike.

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An ultrasonic transducer with two wires attached to it by alligator clips floats very slightly suspended over a glass surface.

A Different Kind Of Ultrasonic Levitation

April 27, 2026 by Aaron Beckendorf 3 Comments

Ultrasonic levitation is by now a familiar trick: one or more ultrasonic transducers create a standing wave, and small objects can be held in the nodes of this standing wave. With a sufficiently large array of transducers, it’s even possible to control the movement of the object. This isn’t the only form of ultrasonic levitation, however, as [Steve Mould] demonstrated with his ultrasonic air hockey table.

This less familiar form of levitation was discovered by [Bob Collins] while working on torpedo guidance systems: when he tried to place a glass lens on an ultrasonic transducer it immediately slid off. He found during further experimentation that an ultrasonic transducer would levitate over any sufficiently flat and smooth surface. It works by trapping a very thin layer of air between the transducer and the smooth surface. When the transducer moves sharply toward the surface, it compresses a layer of air in between, and forces some air out, and the reverse happens while pulling back. However, during the downstroke, the gap through which air can escape is narrower than during the upstroke, and there is more surface-induced drag, meaning that the inflow and outflow of air through a narrow gap isn’t completely equal. At a certain distance, inflow and outflow balance, and the transducer floats on a thin layer of air. Continue reading “A Different Kind Of Ultrasonic Levitation” →

A Solar Powered Plant Monitor That Almost Works

April 23, 2026 by Zoe Skyforest 7 Comments

Keeping plants alive is easy if you’re diligent and never forget to check on your green friends. However, a little electronic help never hurts. To that end, [Narrow Studios] built a simple solar powered monitor to assist in plant maintenance, and it mostly does the job.

An ESP32-C3 development board serves as the brains of the operation. It’s set up with a capacitive soil moisture sensor, a great choice because they tend to last longer than other types. Power is courtesy of a small lithium-polymer battery and a solar panel, which keeps everything running off the juice from interior lighting alone. SK6812 addressable LEDs are used to show current soil moisture status. To avoid excessively draining the batteries with the limited power available, a HCSR505 PIR motion sensor is used to only light the status LEDs if the device detects someone in the vicinity.

There were some issues in the build. The voltage regulator doesn’t supply enough current to enable the ESP32 to jump on WiFi, so soil dryness indication is via LED only. The solar setup is a little weak, too. Still, the project was a great learning experience and with a few mods, would be even more capable.

We’ve featured some great plant monitors over the years, like this Hackaday Prize entry from 2023.

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Making A Bronze Mirror From Scratch

April 17, 2026 by Maya Posch 18 Comments

Although modern-day silvered glass mirrors have pretty much destroyed the market for bronze mirrors, these highly polished pieces of metal once were the pinnacle of mirror technology. Due to the laborious process required these mirrors saw use essentially only by the affluent. That said, how hard would it be to make a bronze mirror today with all of the modern technologies that even a hobbyist can acquire for their shed? Cue [Lundgren Bronze Studios] giving it a shot, starting by casting something flat-ish to start polishing.

Just getting that initial shape to start polishing is a chore, with hammering out the shape possibly being also a viable method. When casting metal it’s tricky to avoid having air bubbles and other defects forming, though using a sand mold seems to help a lot.

After you have the rough shape, polishing using power tools seems like cheating, but as you can see in the video even going from 50 to 8000 grit with a rotating disc left countless scratches. Amusingly, hand sanding did a much better job of removing the worst scratches, following which a polishing compound helped to bring out that literal mirror finish.

A quick glance at the Wikipedia entry for bronze mirrors shows that a tin-bronze alloy like speculum metal was used for thousands of years as it was much easier to polish to a good mirror finish. The metallurgy of what may seem like just a vanity item clearly goes deeper than just polishing up a metal surface.

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Hacking Fermentation For Infinite Pickles From Pass-thru Bioreactor

April 15, 2026 by Tyler August 36 Comments

Home-fermented foods are great– they’re healthier, more flavourful, and cheaper than store-bought alternatives. What they aren’t is convenient: you need to prep a big batch of veggies, let it sit, and then you have to store the excess pickles. If you’re not careful, you end up with ancient, over-fermented pickles at the bottom of the crock, or worse– run out of pickles! Surely a fate worse than death. [Cody] at Cody’s Lab has a solution: a continous-flow fermentation process that keeps just the right supply of pickles coming at all times. Our grandmothers who kept a crock for months in the cold room or root cellar might be confused, but this hack brings pickles into the Just-In-Time framework of the 21st century.

Specifically this is for lactic acid fermentation, the type that gets you kosher dills, saurkraut and kimchi along with a whole mess of other tangy, tasty vegetable treats. Vinegar pickles are a whole other thing. It’s done in a brine, as the lactic acid bacteria are salt tolerant in a way that most things that would rot your food and/or make you sick would not. You can reuse the brine over and over, which is what [Cody] is doing: he crafts a U-shaped crock out of old glass bottles and a couple of pickle jars. He cuts the jars into angled pipe segments that are held together with aquarium sealant, which is apparently food safe. It holds water and looks surprisingly good, in that it isn’t hideous.

The bioreactor gets loaded up with veggies on one end, plus lots of salt and spices to taste, plus some cultured brine from an old batch to kickstart everything. The starter isn’t necessary; it just gets things going faster. The initial packing is the hardest: after filling it the first time, one needs only press new veggies in at one end, while removing tasty treats at the other. A special packing tool [Cody]makes helps with that, but he plans on adding a larger feed side. Thanks to that kickstart, the pickles were ready to try after about a week– which means his tube is a bit long, for his desired dwell time. If you like more fermentation to your pickles, then you might like this size.

May be the first time pickles have been featured on Hackaday without turning them into LEDs. We’ve featured plenty of fermentation projects, with automation to help make the best brew or a build for better tempeh, but not a lot of vegetables.

Thanks to [cam72cam] for the tip!

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A model submarine is shown on a dock. The body of the submarine is made out of a series of acrylic tubes, with other parts made out of grey plastic.

3D-Printed Parts Nearly Sink RC Submarine

April 13, 2026 by Aaron Beckendorf 23 Comments

Of all the remote-control vehicles one can build, a submarine is possibly the hardest: if something goes wrong with almost any other vehicle, it’s easy to recover and repair, but a submarine is a very different affair. This nearly lost [James] of [ProjectAir] his latest project, a 2.7-meter long RC submarine, but it survived to make a few test sails.

Before building the full version, [James] made a test prototype. These submarines use large syringes as ballast tanks, pulling water in and out of the submarine body. The plungers are driven by a lead screw, and have a linear potentiometer for feedback. This can be wired in the same way as a servo motor, making it compatible with the RC controller. The controller receives its signal from an antenna in a buoy tethered to the submarine. Since initial tests worked well, [James] moved on to the full-scale model.

This was made out of radially-arranged acrylic tubes, with all but the top tube left open to the water. At the back of the submarine there were servo-actuated fins and a propeller, which would allow it to steer, ascend, and descend underwater. To waterproof the servo motors, [James] sealed them as much as possible, then filled them with oil. The other water-exposed electronics were either potted in epoxy or coated with a waterproofing compound. During testing, the submarine descended without issue, but was reluctant to resurface. Most of the external components had been 3D printed, and water infiltrated the infill below a certain depth. [James], however, managed to recover it before it was permanently lost, and managed to make a few other dives at a very limited depth.

On the other end of the spectrum from an RC submarine, we’ve also seen a rubber band-powered submarine. We’ve also seen a smaller, but more dive-ready RC submarine. Continue reading “3D-Printed Parts Nearly Sink RC Submarine” →