Why Your Old Phone Sounded The Way It Did

June 2, 2024 by Jenny List 26 Comments

The mobile phone may be sweeping away the traditional wired phone, but that doesn’t change the fascinating history and technology of the older device. At [This Museum Is Not Obsolete] they have a fully functional mechanical telephone exchange as one of their exhibits, and they’ve published a video examining the various sounds it’s capable of making.

When a voice synthesiser was the stuff of science fiction, exchange status couldn’t be communicated by anything but a set of different tones. If you’ve ever encountered a mechanical exchange you’ll recognise the harsh-sounding low-frequency dial tone, and the various sets of beeps denoting different call status. These were produced with a set of oscillators being switched in and out by shaped cams, and the bank of these on their exchange is most of the subject of this video. The common ones such as the engaged tone and the dial tone are explained, but also some we’d never heard such as the one signifying the exchange as out of capacity.

We may never own a mechanical exchange of our own, but we’re glad that someone does and is sharing it with us. You can see the video below the break.

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The end result of the build, a supersized ultrasonic sensor, held in a person's hands

A Super-Size Functional Tribute To An Ultrasonic Sensor

June 1, 2024 by Arya Voronova 6 Comments

Sometimes, it’s time to shut down the oscilloscope, and break out the cardboard and paints. If you’re wondering what for, well, here’s a reminder of an Instructable from [CrazyScience], that brings us back to cardboard crafts days. They rebuild one of the most iconic components for an electronics tinkering beginner — an ultrasonic distance sensor, and what’s fun is, it stays fully functional after the rebuild!

This project is as straightforward as it gets, describing all the steps in great detail, and you can complete it with just a hot glue gun and soldering iron. With materials being simple cardboard, aluminum foil, popsicle sticks, some mesh, and a single ultrasonic sensor for harvesting the transmitter and receiver out of, this is the kind of project you could easily complete with your kids on a rainy day.

Now, the venerable ultrasonic sensor joins the gallery of classics given a size change treatment, like the 555 timer we’ve seen two different takes on, or perhaps that one Arduino Uno. Unlike these three, this project’s cardboard skeleton means it’s all that simpler to build your own, what’s with all the shipping boxes we accumulate.

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Tiny Orrery Is A Watchmaker’s Tour De Force

May 30, 2024 by Dan Maloney 3 Comments

Six tiny gears, a few fancy pins, and some clever casting are what it takes to build this tiny orrery. And patience — a lot of patience, too.

As model solar systems go, this one is exceptionally small. Its maker, [Mike] from Chronova Engineering, says it measures about 20 mm across and qualifies as the smallest orrery around. We can’t officiate that claim, but we’re not going to argue with it either. It’s limited to the Sun-Earth-Moon system, and while not as complete as some other models we’ve seen, it’s still exquisitely detailed. The gears that keep the Moon rotating 12.4 times around the Earth for each rotation of our home planet around the Sun are tiny, and take an abundance of watchmaking skill to pull off.

The video below shows the whole process, which is absolutely entrancing to watch. There are some neat tricks on display, from milling out the arms of the main wheel using a powered tailstock spindle to casting the Sun from resin in a silicone mold. The final model, with the model Earth and Moon spinning around the Sun on delicate brass wheels, is a visual treat.

We’ve seen some interesting stuff from Chronova Engineering lately, including this bimetallic tea timer.

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A person holds a glass jar in their left hand and a spark plug in their right atop a white cylindrical canister. The jar and canister are sitting on top of a green cutting mat.

Spark Plug Becomes Glass Cutter

May 28, 2024 by Navarre Bartz 15 Comments

Sometimes a hack doesn’t need to be rocket science to be useful. Take for instance [MofigoDIY] using an old spark plug to build a glass cutter.

Sure, going to grab a glass cutter at the hardware store might be easy, but there’s something satisfying about going the DIY route. [MofigoDIY]’s version of this classic hack is a bit more refined than the quick and dirty route of smashing the spark plug alumina and hot gluing it into a tube.

After using a rotary tool to cut off the threads and expose the narrow part of the ceramic, [MofigoDIY] grinds it down to a fine point. This lets the spark plug itself become the handle, so you don’t need any additional parts to make the cutter. Toward the end of the video, a heated wire is used to break a glass jar apart after it was scored which might be of interest even if you already have a glass cutter. Once you’re finished making your glass cutter, make sure you dispose of any chips left over, since ceramic spark plug fragments are considered burglary tools in some areas.

Would you rather just build the glass up additively? How about using a laser cutter to sinter glass or 3D printing fused silica using a polymerized composite precursor?

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Rotary Phone Lives On As Arduino Kitchen Timer

May 28, 2024 by Tom Nardi 5 Comments

It’s safe to say that few people still use rotary phones on a daily basis. Hell, most of us don’t even use landline telephones anymore. But just because these classic phones are no longer being used for their original purpose doesn’t necessarily mean they’re doomed to become e-waste.

[Scott-28] recently sent in a particularly well-documented project that turned an antique rotary phone into a digital kitchen timer using an internal Arduino. While we’re not sure practical is a word most folks would use to describe the resulting device, it’s certainly a conversation starter, and the details on how it was all implemented make for an interesting read.

As explained in the README, [Scott-28] first used an oscilloscope to figure out the pulses generated by the phone’s dial. From there, it was relatively easy to connect the dial to one of the pins on an Arduino Uno to determine which numbers the user had entered. The trickier part was getting the original bells to work — in North America, it takes up to 90 VAC to get a phone’s ringer going, which is quite a bit more than the lowly Arduino can handle.

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Grid Leak Radio Draws The Waves

May 23, 2024 by Al Williams 11 Comments

[Stephen McNamera] found a schematic for a grid leak radio online and decided to throw together a few tubes on a piece of wood and see how it worked. As you can see in the video below, it works well. The video is a bit light on details, but the web page he found the plans on also has quite a bit of explanation.

The name “grid leak detector” is due to the grid leak resistor between the grid and ground, in this case, a 2.7 megaohm resistor. The first tube does everything, including AM detection. The second tube is just an audio amplifier that drives the speaker. This demodulation method relies on the cathode to control grid conduction characteristics and was found in radios up to about the 1930s. The control grid performs the usual function but also acts as a diode with the cathode, providing demodulation. In a way, this is similar to a crystal radio but with an amplified tube diode instead of a crystal.

It looks like [Stephen] wound his own coil, and the variable capacitor looks suspiciously like it may have come from an old AM radio. The of the old screw terminal tube sockets on the wood board looks great. Breadboard indeed! What we didn’t see is where the 150 V plate voltage comes from. You hope there is a transformer somewhere and some filter capacitors. Or, perhaps he has a high-voltage supply on the bench.

While tubes are technologically passe, we still like them. Especially in old radios. Just take care around the high voltages, please.

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How To Lace Cables Like It’s 1962

May 20, 2024 by Donald Papp 34 Comments

Cable harnesses made wire management a much more reliable and consistent affair in electronic equipment, and while things like printed circuit boards have done away with many wires, cable harnessing still has its place today. Here is a short how-to on how to lace cables from a 1962 document, thoughtfully made available on the web by [Gary Allsebrook] and [Jeff Dairiki].

It’s a short resource that is to the point in all the ways we love to see. The diagrams are very clear and the descriptions are concise, and everything is done for a reason. The knots are self-locking, ensuring that things stay put without being overly tight or constrictive.

According to the document, the ideal material for lacing cables is a ribbon-like nylon cord (which reduces the possibility of biting into wire insulation compared to a cord with a round profile) but the knots and techniques apply to whatever material one may wish to use.

Cable lacing can be done ad-hoc, but back in the day cable assemblies were made separately and electrically tested on jigs prior to installation. In a way, such assemblies served a similar purpose to traces on a circuit board today.

Neatly wrapping cables really has its place, and while doing so by hand can be satisfying, we’ve also seen custom-made tools for neatly wrapping cables with PTFE tape.