TV Repair By Mail

November 17, 2022 by 49 Comments

I don’t think there was ever a correspondence school called the “Close Cover Before Striking School” but since book matches — which used to be a thing when most people smoked — always had that text on them anyway perhaps there should have been. There was a time when electronic magazines, billboards, and even book matches were constantly bombarding us with ads to have a career in electronics. Or computers. Or TV repair. So while we think of distance learning as a new idea, really it is just the evolution of these old correspondence schools which date back quite some time.

How far exactly? Hard to say. There’s evidence of some distance learning going back as far as 1728. In 1837, there was a correspondence course to learn shorthand. By 1858, the University of London started its external program for correspondence work and the University of Chicago had a home study division in 1892.  Radio was an early choice of topic, too. In the United States, the United Wireless Telegraph company started a training school — later the Marconi Institute — in 1909. However, it is doubtful that there was any correspondence training going on there until much later.

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Sappers clearing the last mines from the beach front of a former French luxury hotel, now in use as a rest club for troops of 3rd Division, 15 July 1944.

The Long Tail Of War: Finding Unexploded Ordnance Before It Finds Us

September 19, 2022 by 38 Comments

Long after the enemy forces have laid down their arms, peace accords have been signed and victories celebrated, there is still a heavy toll to be paid. Most of this comes in the form of unexploded ordnance, including landmines and the severe pollution from heavy metals and other contaminants that can make large areas risky to lethal to enter. Perhaps the most extreme example of this lasting effect is the Zone Rouge (Red Zone) in France, which immediately after the First World War came to a close comprised 1,200 square kilometers.

Within this zone, contamination with heavy metals is so heavy that some areas do not support life, while unexploded shells – some containing lethal gases – and other unexploded ordnance is found throughout the soil. To this day much of the original area remains off-limits, though injuries from old, but still very potent ordnance are common around its borders. Clean-up of the Zone Rouge is expected to take hundreds of years. Sadly, this a pattern that is repeated throughout much of the world. While European nations stumble over ordnance from its two world wars, nations in Africa, Asia and elsewhere struggle with the legacy from much more recent conflicts.

Currently, in Europe’s most recent battlefield, more mines are being laid, booby traps set and unexploded shells and other ordnance scattered where people used to live. Clearing these areas, to make them safe for a return of their inhabitants has already begun in Ukraine, but just like elsewhere in the world, it is an arduous and highly dangerous process with all too often lethal outcomes.

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Induction Heater Uses New Coil

June 8, 2022 by 14 Comments

Induction cook tops are among the most efficient ways of cooking in the home that are commercially available to the average person. Since the cook surface uses magnetic fields to generate heat in the cookware itself, there is essentially no heat wasted. There are some other perks too, such as faster cooking times and more fine control, not to mention that it’s possible to build your own induction stove. All you need is some iron, wire, and a power source, and you can have something like this homemade induction cooker.

This induction heater has a trick up its sleeve, too. Instead of using an air coil to generate heat in the cookware, this one uses an iron core instead. The project’s creator [mircemk] built an air core induction stove in the past, and this new one is nearly identical with the exception of the addition of the iron core. This allows for the use of less wire, and uses a driver circuit called a Mazzilli ZVS driver running through some power MOSFETs to power the device. A couple inductors limit the current to 20A, but it appears to work just as well as the previous stove.

This build puts a homemade induction stove well within reach of anyone with an appropriate power supply and enough wire and inductors to build the coils. [mircemk] has made somewhat of a name for himself involving project that use various coils of wire, too, like this project we featured recently which uses two overlapping air-core coils to build an effective metal detector.

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Treasure Hunting With A Handful Of Common Components

November 15, 2021 by 16 Comments

Sometimes simpler is better — when you don’t need the the computational power of an onboard microcontroller, it’s often best to rely on a simple circuit to get the job done. With cheap Raspberry Pis and ESP32s all over the place, it can be easy to forget that many simpler projects can be completed without a single line of code (and with the ongoing chip shortage, it may be more important now than ever to remember that).

[mircemk] had the right idea when he built his simple induction-balance metal detector. It uses a couple of 555 timers, transistors, and passives to sense the presence of metallic objects via a coil of wire. He was able to detect a coin up to 15 cm away, and larger objects at 60cm — not bad for a pile of components you probably have in your bench’s spare parts drawer right now! The detector selectivity can be tuned by a couple of potentiometers, and in true metal detector fashion, it has a buzzer to loudly blare at you once it’s found something (along with a LED, in case the buzzer gets too annoying).

All in all, this metal detector looks like a terribly fun project — one perfectly suited to beginners and more seasoned hackers alike. It serves as a great reminder that not every project needs WiFi or an OLED display to be useful, but don’t let that stop you from overdoing things! If touchscreens are more your speed, [mircemk] has got you covered with a smartphone-integrated version as well.

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Arduino Finds Treasure

August 12, 2021 by 6 Comments

A beach is always a relaxing summer vacation destination, a great place to hang out with a drink and a book or take a swim in the ocean. For those who need a more active beach-going activity with an electronics twist, though, metal detecting is always a popular choice too. And, of course, with an Arduino and some know-how it’s possible to build a metal detector that has every feature you could want from even a commercial offering.

This build comes to us from [mircemk] who built this metal detector around an Arduino Nano and uses a method called induction balance detection to find metal. Similar to how radar works, one coil sends out a signal and the other listens for reflections back from metal objects underground. Building the coils and determining their resonant frequency is the most important part of this build, and once that is figured out the rest of the system can be refined and hidden treasure can easily be unearthed.

One of the more interesting features of this build is its ability to discriminate between ferrous and non-ferrous metals, and it can detect large metal objects at distances of more than 50 cm. There are improvements to come as well, since [mircemk] plans to increase power to the transmission coil which would improve the range of the device. For some of [mircemk]’s other metal detectors, be sure to check out this one which uses a smartphone to help in the metal detection process.

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Variable Mirror Changes Shape Under Pressure

June 27, 2020 by 10 Comments

Unless you’re in a carnival funhouse, mirrors are generally dead flat and kind of boring. Throw in some curves and things get interesting, especially when you can control the curve with a touch of your finger, as with this variable surface convex mirror.

The video below starts off with a long but useful review of conic constants and how planes transecting a cone can create circles, parabolas, or ellipses depending on the plane’s angle. As [Huygens Optics] explains, mirrors ground to each of these shapes have different properties, which makes it hard to build telescopes that work at astronomical and terrestrial distances. To make a mirror that works over a wide range of distances, [Huygens Optics] built a mirror from two pieces of glass bonded together to form a space between the front and rear surface. The front surface, ground to a spherical profile, can be deformed slightly by evacuating the plenum between the two surfaces with a syringe. Atmospheric pressure bends the thinner front surface slightly, changing the shape of the mirror.

[Huygens Optics] also built an interferometer to compare the variable mirror to a known spherical reference. The data from the interferometer was fed to a visualization package that produced maps of the surface shape, which you can easily see changing as the pressure inside the mirror changes. Alas, a deeper dive into the data showed the mirror to be less than perfect, but it’s fascinating to think that a mirror can flex enough to change from elliptical to almost parabolic with nothing more than a puff of air.

We’ve seen a couple of interesting efforts from [Huygens Optics] before, including this next-level spirit level. He’s not all about grinding glass, though — witness this investigation into discriminating metal detectors.

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Hackaday Podcast 066: The Audio Overdub Episode; Tape Loop Scratcher, Typewriter Simulator, And Relay Adder

May 8, 2020 by 3 Comments

Hackaday editors Elliot Williams and Mike Szczys stomp through a forest full of highly evolved hardware hacks. This week seems particularly plump with audio-related projects, like the thwack-tackular soldenoid typewriter simulator. But it’s the tape-loop scratcher that steals our hearts; an instrument that’s kind of two-turntables-and-a-microphone meets melloman. We hear the clicks of 10-bit numbers falling into place in a delightful adder, and follow it up with the beeps and sweeps of a smartphone-based metal detector.

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!

Direct download (60 MB or so.)

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