Author: Jenny List

3387 Articles

It’s A Variable Capacitor, But Not As We Know It

September 17, 2025 by 22 Comments

Radio experimenters often need a variable capacitor to tune their circuits, as the saying goes, for maximum smoke. In decades past these were readily available from almost any scrap radio, but the varicap diode and then the PLL have removed the need for them in consumer electronics. There have been various attempts at building variable capacitors, and here’s [radiofun232] with a novel approach.

A traditional tuning capacitor has a set of meshed semicircular plates that have more of their surface facing each other depending on how far their shaft is turned. The capacitor presented in the first video below has two plates joined by a hinge in a similar manner to the covers of a book. It’s made of tinplate, and the plates can be opened or closed by means of a screw.

The result is a capacitor with a range from 50 to 150 picofarads, and in the second video we can see it used with a simple transistor oscillator to make a variable frequency oscillator. This can form the basis of a simple direct conversion receiver.

We like this device, it’s simple and a bit rough and ready, but it’s a very effective. If you’d like to see another unusual take on a variable capacitor, take a look at this one using drinks cans.

Continue reading “It’s A Variable Capacitor, But Not As We Know It” →

The Practicality Of Solar Powered Meshtastic

September 17, 2025 by 19 Comments

A Meshtastic node has been one of the toys of the moment over the last year, and since they are popular with radio amateurs there’s a chance you’ll already live within range of at least one. They can typically run from a lithium-ion or li-po battery, so it’s probable that like us you’ve toyed with the idea of running one from a solar panel. It’s something we have in common with [saveitforparts], whose experiments with a range of different solar panels form the subject of a recent video.

He has three different models: one based around a commercial solar charger, another using an off-the-shelf panel, and a final one using the panel from a solar garden light. As expected the garden light panel can’t keep an ESP32 with a radio going all day, but the other two manage even in the relatively northern climes of Alaska.

As a final stunt he puts one of the nodes out on a rocky piece of the southern Alaskan coastline, for any passing hacker to find. It’s fairly obviously in a remote place, but it seems passing cruise ships will be within its range. We just know someone will take up his challenge and find it.

Continue reading “The Practicality Of Solar Powered Meshtastic” →

How To Have A Medium Format Camera Without Breaking The Bank

September 16, 2025 by 11 Comments

For most people, experimentation with film photography comes in the form of the 35 mm format. Its ubiquity in snapshot photography means cameras are readily available at all levels, and the film offers a decent compromise between resolution and number of shots per dollar spent.

For those who wish to take their film photography further there’s the so-called medium format 120 roll film, but here opting for a higher-end camera can become expensive. Fortunately [Javier Doroteo] is here with a 3D printed medium format camera designed to use lenses intended for the Mamiya Press cameras, and from where we’re sitting it looks very nicely designed indeed.

All the files can be found on Printables along with a list of the other parts required. It’s made simple by the Mamiya lenses incorporating the shutter, but there’s still a lot of attention that has been paid to the back of the camera. This is the third version of the design and it shows, details such as the film holder and light proofing are well thought out.

Photography is so often a world in which collecting the latest kit is seen as more important than the photographs themselves, so we like and encourage camera hackers as a reaction to all that. If you’d like to see another medium format camera, this certainly isn’t the first we’ve brought you.

This Rail Speeder Needs A Little Work

September 16, 2025 by 30 Comments

If you take the wheels off a FIAT Punto, you might just notice that those rims fit nicely on a rail. [AT Lab] did, and the resulting build makes for a very watchable video.

Some of us have been known to spend a little too much time chasing trains, and there’s little on rails that won’t catch a railfan’s eye. That goes for rail speeders too, home constructed railcarts for exploring abandoned lines, and there are some great builds out there. We like the one in the video below the break, but we can’t help noticing a flaw which might just curtail its career.

It’s a simple enough build, a wooden chassis, a single motor and chain drive to one axle. All the wheel fittings are 3D printed, which might be a case of using the one tool you have to do everything, but seems to work. It rides well on the test track which appears to be an abandoned industrial siding, but it’s in those wheels we can see the problem and we guess that perhaps the builder is not familiar with rails. The Punto wheels have an inner rim and an outer rim, while a true rail wheel only has an inner one. There’s a good reason for this; real railways have points and other trackwork, not to mention recessed rails at road crossings or the like. We love the cart, but we’d cut those inner rims off to avoid painful derailments.

If you’re up for the ultimate railway build, take care not to go near a live line, and make sure you follow this video series.

Continue reading “This Rail Speeder Needs A Little Work” →

UTF-8 Is Beautiful

September 14, 2025 by 30 Comments

It’s likely that many Hackaday readers will be aware of UTF-8, the mechanism for incorporating diverse alphabets and other characters such as 💩 emojis. It takes the long-established 7-bit ASCII character set and extends it into multiple bytes to represent many thousands of characters. How it does this may well be beyond that basic grasp, and [Vishnu] is here with a primer that’s both fascinating and easy to read.

UTF-8 extends ASCII from codes which fit in a single byte, to codes which can be up to four bytes long. The key lies in the first few bits of each byte, which specify how many bytes each character has, and then that it is a data byte. Since 7-bit ASCII codes always have a 0 in their most significant bit when mapped onto an 8-bit byte, compatibility with ASCII is ensured by the first 128 characters always beginning with a zero bit. It’s simple, elegant, and for any of who had to deal with character set hell in the days before it came along, magic.

We’ve talked surprisingly little about the internals of UTF-8 in the past, but it’s worthy of note that this is our second piece ever to use the poop emoji, after our coverage of the billionth GitHub repository.

Emoji bales: Tony Hisgett, CC BY 2.0.

Round And Round With A Tape Delay Synth

September 11, 2025 by 7 Comments

Over the years we’ve been entertained by an array of musical projects from [Look Mum No Computer], and his latest is no exception. It’s a tape delay, loop generator, and synth all in one. Confused? That’s what you get if you position a load of tape heads around a rotating disk with magnetic tape on its perimeter.

Taking a circular piece of inch-thick Perspex, he wraps a length of one inch tape round its perimeter. This is placed as though it were a turntable on a stepper motor with variable speed, and the tape heads are positioned around its edge. Each read head feeds its own preamp which in turn drives a mixer array, and there’s also a record head and an erase head. If you’ve ever played with tape loops you’ll immediately understand the potential for feedback and sequence generation to make interesting sounds. There’s a lot of nuance to the build, in designing the mount for the motor to stop the enclosure flexing, in using a gearbox for increased torque, and in balancing the disk.

The result is as much an effect as it is an instrument in its own right, particularly in its prototype phase when the read head was movable. We’re treated to a demo/performance, and we look forward to perhaps seeing this in person at some point. There’s a future video promised in which a fix should come for a click caused by the erase circuitry, and he’ll make a more compact enclosure for it. Continue reading “Round And Round With A Tape Delay Synth” →

Reverse Engineering A Robot Mower’s Fence

September 10, 2025 by 19 Comments

There are a variety of robot mower systems on the market employing different navigation methods, and [Eelco] has the story of how one of these was reverse engineered. Second hand Roomba lawnmowers kept appearing for very low prices without the electronics driving the buried-wire fence that keeps them from going astray. The story of their reverse engineering provides us with a handy insight into their operation.

The wire fence is a loop of wire in the ground, so it was modeled using a few-ohm resistor and the waveform across it from a working driver captured with an oscilloscope. The resulting 3 kHz waveform surprisingly to us at least doesn’t appear to encode any information, so it could be replicated easily enough with an ESP32 microcontroller. An LM386 audio amplifier drives the loop, and with a bit of amplitude adjustment the mower is quite happy in its fake fence.

Robot mower hacking has become quite the thing around here.