Half Crystal Radio, Half Regenerative Radio

A rite of passage in decades past for the electronics experimenter was the crystal radio. Using very few components and a long wire antenna, such a radio could pick up AM stations with no batteries needed, something important in the days when a zinc-carbon cell cost a lot of pocket money. The days of AM broadcasting may be on the wane, but it’s still possible to make a crystal set that will resolve stations on the FM band. [Andrea Console] has done just that, with a VHF crystal set that whose circuit also doubles as a regenerative receiver when power is applied.

The key to a VHF crystal set lies in the highest quality tuned circuit components to achieve that elusive “Q” factor. In this radio that is coupled to a small-signal zero voltage threshold FET that acts as a detector when no power is applied, and the active component in a regenerative radio when it has power. The regenerative radio increases sensitivity and selectivity by operating at almost the point of oscillation, resulting in a surprisingly good receiver for so few parts. Everyone should make a regenerative radio receiver once in their life!

Testing Part Stiffness? No Need To Re-invent The Bending Rig

If one is serious about testing the stiffness of materials or parts, there’s nothing quite like doing your own tests. And thanks to [JanTec]’s 3-Point Bending Test rig, there’s no need to reinvent the wheel should one wish to do so.

The dial caliper can be mounted to a fixed height, thanks to a section of 3030 T-slot extrusion.

Some simple hardware, a couple spare pieces of 3030 T-slot extrusion, a few 3D-printed parts, and a dial indicator all come together to create a handy rig that will let one get straight to measuring.

Here is how it works: stiffness of a material is measured by placing a sample between two points and applying a known force to the middle of the sample. This will cause the material to bend, and measuring how far a standardized sample deforms under a known amount of force (normally accomplished by a dial indicator) is how one can quantify a material’s stiffness.

When a material talks about its Young’s modulus (E) value, it’s talking about stiffness. A low Young’s modulus means a material is more elastic, a high value means the material is more stiff. (This shouldn’t be confused with strength or toughness, which are more about resistance to non-recoverable deformation, and resistance to fracture, respectively.)

Interested in results, but don’t want to get busy doing your own testing? Someone’s already been there and done that: here’s a great roundup of measurements of 3D-printed parts, using different filaments.

$60 Robot Arm Is Compact

Thanks to 3D printing and inexpensive controllers, a robot arm doesn’t need to break the bank anymore. Case in point? [Build Some Stuff] did a good-looking compact arm with servos for under $60. The arm uses an interesting control mechanism, too.

Instead of the traditional joystick, the arm has a miniature arm with potentiometers at each joint instead of motors. By moving the model arm to different positions, the main arm will mimic your motions. It is similar to old control systems using a synchro (sometimes called a selsyn), but uses potentiometers and servo motors.

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Messing With A Cassette Player Never Sounded So Good

Cassette players and tapes are fertile hacking ground. One reason is that their electromechanical and analog nature provides easy ways to fiddle with their operation. For example, slow down the motor and the playback speed changes accordingly. As long as the head is moving across the tape, sound will be produced. The hacking opportunities are nicely demonstrated by [Lara Grant]’s cassette player mod project.

The device piggybacks onto a battery-powered audio cassette player and provides a variety of ways to fiddle with the output, including adjustable echo and delay, and speed control. At the heart of the delay and echo functionality is the PT2399, a part from the late 90s capable of some pretty impressive audio effects (as long as a supporting network of resistors and capacitors are in place, anyway.)

[Lara] provides a schematic for the PT2399’s interface to the cassette player’s output, which is handy should anyone want to try a similar modification. Speed of playback is controlled by adjusting the cassette player’s motor with PWM. Volume control swaps a photocell in place of a rotary volume potentiometer, and additional audio jacks provide flexibility for mixing and matching input and output with other equipment.

You can see it in action in the video embedded below. Intrigued, and want a few more examples of modified tape players? How about a strange sort of cassette synth, or this unique take on a mellotron that uses a whopping 14 modified tape players under the hood? And really out there is the Magnetotron, which consists of a large rotating cylinder with tape loops stuck to it — the magnetic read head is mounted on a wand which the user manually moves across the tapes to create sounds.

Tape players are accessible, hackable things, so remember to drop us a line if you make something neat!

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Op Amp Contest: Go Down An Octave, No FFT, No PLL, No Oscillator!

We like a project that makes us think, and that was certainly the case with [MS-BOSS]’s octave downshifter that’s an entry in our current op-amp contest. Instead of resorting to an FFT, or a PLL, it uses a technique best described as a custom analogue computer to implement the maths of octave downshifting. It’s an extremely clever approach, and we don’t mind admitting took us more than one read to understand how it works.

Just as you would with any mathematical problem, he’s split the job of halving the frequency into its constituent mathematical functions. The square root calculation circuit is probably the one that most required the dredging up of dimly-remembered analogue circuitry undergraduate courses for us.

The result is a fascinating read that’s well worth taking the time to understand if you have any interest in analogue electronics. It’s by no means the easiest way to make this particular effect in 2023, as we’re much more used to seeing our community make digital effects, but if you fancy yourself as any kind of op-amp designer, you really need to give it a look.

Warmer Ice Cream?

What if you could tweak the recipe on ice cream to keep it frozen at higher temperatures? The idea comes from massive conglomerate Unilever. Among other things, the brand owns a wide variety of ice cream brands, from Ben & Jerry’s to the Magnum and Cornetto lines. Instead of running freezers at the industry standard of -18 °C (0°F), the company is experimenting with upping the temperature to -12 °C (10 °F) instead.

First off, you’d save a lot of electricity. Thanks to the way the industry works, the company actually owns the vast majority of the three million or so display freezers that are used to sell its stock to customers. Running at a higher temperature could slash the freezer’s energy use by 20% to 30%, according to the company’s calculations. The company also estimates that the energy used by these freezers makes up around 10% of its total greenhouse gas footprint, so it’s better for the environment too.

Of course, there’s savvy commercial reasons behind the idea. Unilever had noticed its ice cream sales dropping in 2022. The company believes this was in part due to retailers unplugging their freezers earlier than usual as winter approached, due to high energy bills. If the company’s freezers aren’t humming, they’re doing less business. If shaving down the freezer’s energy use helps retailers keep them plugged in and the lights on, that’s a net bonus to the company’s bottom line. It could also make their freezers unhospitable places for rival products, giving them an edge in the marketplace.

But this is all business intrigue. Let’s instead take a deeper look at ice cream.

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Chatting With Local AI Moves Directly In-Browser, Thanks To Web LLM

Large Language Models (LLM) are at the heart of natural-language AI tools like ChatGPT, and Web LLM shows it is now possible to run an LLM directly in a browser. Just to be clear, this is not a browser front end talking via API to some server-side application. This is a client-side LLM running entirely in the browser.

The ability to run an LLM (natural language AI) directly in-browser means more ways to implement local AI while enjoying GPU acceleration via WebGPU.

Running an AI system like an LLM locally usually leverages the computational abilities of a graphics card (GPU) to accelerate performance. This is true when running an image-generating AI system like Stable Diffusion, and it’s also true when implementing a local copy of an LLM like Vicuna (which happens to be the model implemented by Web LLM.) The thing that made Web LLM possible is WebGPU, whose release we covered just last month.

WebGPU provides a way for an in-browser application to talk to a local GPU directly, and it sure didn’t take long for someone to get the idea of using that to get a local LLM to run entirely within the browser, complete with GPU acceleration. This approach isn’t just limited to language models, either. The same method has been applied to successfully create Web Stable Diffusion as well.

It’s a fascinating (and fast) development that opens up new possibilities and, hopefully, gives people some new ideas. Check out Web LLM’s GitHub repository for a closer look, as well as access to an online demo.