Designing A Tone Control Properly

April 8, 2025 by Jenny List 12 Comments

Many years ago, audio equipment came with a tone control, a simple RC filter that would cut or boost the bass to taste. As time passed, this was split into two controls for bass and treble, and then finally into three for bass, mid, and treble. When audiophile fashion shifted towards graphic equalisers, these tone controls were rebranded as “3-band graphic equalisers”, a misleading term if ever we heard one. [Gabriel Dantas] designed one of these circuits, and unlike the simple passive networks found on cheap music centres of old, he’s doing a proper job with active filters.

The write-up is worth a read even if you are not in the market for a fancy tone control, for the basic primer it gives on designing an audio filter. The design contains, as you might expect, a low-pass, a bandpass, and a high-pass filter. These are built around TL072 FET-input op-amps, and an LM386 output stage is added to drive headphones.

The final project is built on a home-made PCB, complete with mains power supply. Audiophiles might demand more exotic parts, but we’re guessing that even with these proletarian components it will still sound pretty good. Probably better than the headphone amplifier featured in a recent project from a Hackaday writer, at least. There’s a build video, below the break.

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The Computers Of EPCOT

April 8, 2025 by Al Williams 8 Comments

Even if you aren’t a Disney fan, you probably know about EPCOT — Experimental Prototype Community of Tomorrow — a Disney attraction that promised a glimpse of the future. [ErnieTech] takes a glimpse at the UNIVAC computer that ran the operation in the 1980s. A lot of schools had UNIVAC 1100-series computers back in those days, so while you don’t hear as much about them as, say, IBM 360s, there are hordes of people who have used the 1100s, even if they don’t remember it.

EPCOT opened in 1982, and the UNIVAC not only ran the attraction but was also visible as part of the exhibit’s ambiance. They even used the Pepper’s Ghost illusion to superimpose a little man on top of the equipment.

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FreeDOS 1.4 Released

April 8, 2025 by Maya Posch 22 Comments

Even in 2025 there are still many applications for a simple Disk Operating System (DOS), whether this includes running legacy software (including MS-DOS games & Windows 3.x), or (embedded) systems running new software where the overhead of a full-fat Linux or BSD installation would be patently ridiculous.

This is where the FreeDOS project provides a modern, fully supported DOS, with the recent 1.4 release adding a whole range of features and updates to existing components like the FreeCOM command shell. This is the first stable release since 1.3 was released in 2022.

FreeDOS saw its first release in 1994 and has become the de facto replacement for MS-DOS — featuring many improvements to make it work well on modern hardware and a package manager to manage installed software much like on Linux & BSD. The new kernel didn’t quite make it into this release, but it and some other items will be available in the monthly test builds.

You can download the new 1.4 release here, with live & installer CD images, a USB installer and even a Floppy Edition available. System requirements include an (Intel) x86 CPU, a BIOS (or legacy UEFI mode), 640 kB of RAM and 20 MB of storage.

Turning Old Cellphones Into SBCs

April 8, 2025 by Elliot Williams 35 Comments

[David] sent us a tip about a company in Belgium, Citronics, that is looking to turn old cellphones into single-board computers for embedded Linux applications. We think it’s a great idea, and have long lamented how many pocket supercomputers simply get tossed in the recycling stream, when they could be put to use in hacker projects. So far, it looks like Citronics only has a prototyping breakout board for the Fairphone 2, but it’s a promising idea.

One of the things that’s stopping us from re-using old phones, of course, is the lack of easy access to the peripherals. On the average phone, you’ve got one USB port and that’s it. The Citronics dev kit provides all sorts of connectivity: 4x USB 2.0, 1x Ethernet 10/100M, and a Raspberry Pi Header (UART, SPI, I2C, GPIO). At the same time, for better or worse, they’ve done away with the screen and its touch interface, and the camera too, but they seem to be keeping all of the RF capabilities.

The whole thing runs Linux, which means that this won’t work with every phone out there, but projects like PostmarketOS and others will certainly broaden the range of usable devices. And stripping off the camera and screen has the secondary advantages of removing the parts that get most easily broken and have the least support from custom Linux distros.

We wish we had more details about the specifics of the break-out boards, but we like the idea. How long before we see an open-source implementation of something similar? There are so many cheap used and broken cellphones out there that it’s certainly a worthwhile project!

LayerLapse Simplifies 3D Printer Time-lapse Shots

April 8, 2025 by Tom Nardi 15 Comments

We know you’ve seen them: the time-lapses that show a 3D print coming together layer-by-layer without the extruder taking up half the frame. It takes a little extra work compared to just pointing a camera at the build plate, but it’s worth it to see your prints materialize like magic.

Usually these are done with a plugin for OctoPrint, but with all due respect to that phenomenal project, it’s a lot to get set up if you just want to take some pretty pictures. Which is why [Whopper Printing] put together the LayerLapse. This small PCB is designed to trigger your DSLR or mirrorless camera once its remotely-mounted hall effect sensor detects the presence of a magnet.

The idea is that you just need to stick a small magnet to your extruder, add a bit of extra G-code that will park it over the sensor at the end of each layer, and you’re good to go. There’s even a spare GPIO pin broken out should you want to trigger something else on each layer of your print. Admittedly we can’t think of anything else right now that would make sense, other than some other type of camera, but we’re sure some creative folks out there could put this feature to use.

Currently, [Whopper Printing] is selling the LayerLapse as a finished product, though it does sound like a kit version is in the works. There’s also instructions for building a DIY version of the hardware using your microcontroller of choice. Whether you buy or build the hardware, the firmware is available under the MIT license for your tinkering pleasure.

Being hardware hackers, we appreciate the stand-alone nature of this solution. But if you’re already controlling your printer through OctoPrint, you’re probably better off just setting up one of the available time-lapse plugins.

Printed Robotic Arm Pumps Up With Brushless Motors

April 8, 2025 by Tom Nardi 17 Comments

[JesseDarr] recently wrote in to tell us about their dynamic Arm for Robitc Mischief (dARM), a mostly 3D printed six degrees of freedom (6DOF) robotic arm that’s designed to be stronger and more capable than what we’ve seen so far from the DIY community.

The secret? Rather than using servos, dARM uses brushless DC (BLDC) motors paired with ODrive S1 controllers. He credits [James Bruton] and [Skyentific] (two names which regular Hackaday readers are likely familiar with) for introducing him to not only the ODrive controllers, but the robotics applications for BLDCs in the first place.

dARM uses eight ODrive controllers on a CAN bus, which ultimately connect up to a Raspberry Pi 4B with a RS485 CAN Hat. The controllers are connected to each other in a daisy chain using basic twisted pair wire, which simplifies the construction and maintenance of the modular arm.

As for the motors themselves, the arm uses three different types depending on where they are located, with three Eaglepower 8308 units for primary actuators, a pair of GB36-2 motors in the forearm, and finally a GM5208-24 for the gripper. Together, [JesseDarr] says the motors and gearboxes are strong enough to lift a 5 pound (2.2 kilogram) payload when extended in a horizontal position.

The project’s documentation includes assembly instructions for the printed parts, a complete Bill of Materials, and guidance on how to get the software environment setup on the Raspberry Pi. It’s not exactly a step-by-step manual, but it looks like there’s more than enough information here for anyone who’s serious about building a dARM for themselves.

If you’d like to start off by putting together something a bit easier, we’ve seen considerably less intimidating robotic arms that you might be interested in.

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The 1980s Computer, French Style

April 7, 2025 by Jenny List 10 Comments

Should you travel around Europe, you may notice that things in France are ever so slightly different. Not necessarily better or worse, simply that the French prefer to plough their own furrow rather than importing cultural tends from their neighbors.

In the 1980s this was evident in their home computers, because as well as a Minitel terminal in your house, you could have an all-French machine plugged into your TV. [Retro Krazy] has just such a machine — it’s a Matra Hachette Alice 32, and its red plastic case hides hardware any of us would have been proud to own back in the day.

At first sight it appears superficially similar to a Sinclair Spectrum, with its BASIC keywords next to the keys. But under that slightly calculator style AZERTY keyboard is an entirely different architecture, a Motorola 6803. The first Alice computer was a clone of a Radio Shack model, and while this one has no compatibility with its predecessor it retains some silicon choices. On the back are a series of DIN sockets, one for a SCART adapter, and more for serial connectivity and a cassette deck. The overall impression is of a well-engineered machine, even if that red color is a little garish.

The Alice hasn’t appeared here on its own before, but we have taken a look at French retrocomputers here in the past.

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