Writing A GPS Receiver From Scratch

March 18, 2025 by 22 Comments

GPS is an incredible piece of modern technology. Not only does it allow for locating objects precisely anywhere on the planet, but it also enables the turn-by-turn directions we take for granted these days — all without needing anything more than a radio receiver and some software to decode the signals constantly being sent down from space. [Chris] took that last bit bit as somewhat of a challenge and set off to write a software-defined GPS receiver from the ground up.

As GPS started as a military technology, the level of precision needed for things like turn-by-turn navigation wasn’t always available to civilians. The “coarse” positioning is only capable of accuracy within a few hundred meters so this legacy capability is the first thing that [Chris] tackles here. It is pretty fast, though, with the system able to resolve a location in 24 seconds from cold start and then displaying its information in a browser window. Everything in this build is done in Python as well, meaning that it’s a great starting point for investigating how GPS works and for building other projects from there.

The other thing that makes this project accessible is that the only other hardware needed besides a computer that runs Python is an RTL-SDR dongle. These inexpensive TV dongles ushered in a software-defined radio revolution about a decade ago when it was found that they could receive a wide array of radio signals beyond just TV.

Interposer Helps GPS Receiver Overcome Its Age

March 4, 2025 by 5 Comments

We return to [Tom Verbeure] hacking on Symmetricom GPS receivers. This time, the problem’s more complicated, but the solution remains the same – hardware hacking. If you recall, the previous frontier was active antenna voltage compatibility – now, it’s rollover. See, the GPS receiver chip has its internal rollover date set to 18th of September 2022. We’ve passed this date a while back, but the receiver’s firmware isn’t new enough to know how to handle this. What to do? Build an interposer, of course.

You can bring the module up to date by sending some extra init commands to the GPS chipset during bootup, and, firmware hacking just wasn’t the route. An RP2040 board, a custom PCB, a few semi-bespoke connectors, and a few zero-ohm resistors was all it took to make this work. From there, a MITM firmware wakes up, sends the extra commands during power-on, and passes all the other traffic right through – the system suspects nothing.

Everything is open-source, as we could expect. The problem’s been solved, and, as a bonus, this implant gives a workaround path for any future bugs we might encounter as far as GPS chipset-to-receiver comms are concerned. Now, the revived S200 serves [Tom] in his hacking journeys, and we’re reminded that interposers remain a viable way to work around firmware bugs. Also, if the firmware (or the CPU) is way too old to work with, an interposer is a great first step to removing it out of the equation completely.

A picture of the Alarmo running a tweaked firmware, showing a theme with (Debug) added to its name, obviously a firmware modification

Making The Alarmo Customizable, By Any Means Necessary

March 2, 2025 by 6 Comments

Last year, Nintendo has released the Alarmo, a bedside-style alarm clock with a colourful display. Do you own one? You deserve full control over your device, of course. [KernelEquinox] has been reverse-engineering an Alarmo ever since getting one, and there’s no shortage of cool stuff you’ll be able to do with an Alarmo thanks to this work.

Now, just how can you improve upon the Alarmo? Looking through the Alarmo dev community site and threads on the subreddit, there are plenty of ideas, from themes to a ton of possible behaviour tweaks! In particular, Nintendo has already changed Alarmo’s behaviour in a way that is jarring to some users – a third-party development community will help us all make sure our Alarmos work exactly like we expect them to. Want to replace the sound files,  tie your Alarmo into your smart home setup, write your apps, tweak the UI or default behaviour, fix a bug that irks you real bad, or access a debug menu? Or, ensure that Alarmo doesn’t contribute to light pollution in your room? All appears to be doable.

Like the Alarmo, but don’t own one yet? They’re limited-release for now, but it will be more widely available this March; we thank [KernelEquinox] for the work in making Alarmo hacker-friendly. If you’ve forgotten, this project started off thanks to the efforts of [Gary] last year. We covered it back then — cat pictures included!

Magnetic Vise Makes Positioning Your Workpiece Easier

February 14, 2025 by 12 Comments

[Chris Borge] was doing some fine tapping operations, and wanted a better way to position his workpieces. This was critical to avoid breaking taps or damaging parts. To this end, he whipped up a switchable magnetic vice to do the job.

The key to the build is that the magnetic field can be switched on and off mechanically. This is achieved by having two sets of six magnets each. When the poles of both sets of magnets are aligned, the magnetic field is effectively “on.” When the poles are moved to oppose each other, they effectively cancel each other out, turning the field “off.” [Chris] achieved this functionality with 12 bar magnets, 12 M12 nuts, and a pair of 3D-printed rings. Rotating the rings between two alignments serves to switch the set up on or off. The actual switching mechanism is handled with a cam and slider setup which allowed [Chris] to build a convenient vice with a nice large working area. He also took special effort to ensure the device wouldn’t pick up large amounts of ferrous swarf that would eventually clog the mechanism.

It’s a neat build, and one you can easily recreate yourself. [Chris] has supplied the files online for your printing pleasure. We’ve featured some other types of magnetic vise before, too. Video after the break.

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It’s Always Pizza O’Clock With This AI-Powered Timepiece

February 11, 2025 by 11 Comments

Right up front, we’ll say that [likeablob]’s pizza-faced clock gives us mixed feelings about our AI-powered future. On the one hand, if that’s Stable Diffusion’s idea of what a pizza looks like, then it should be pretty easy to slip the virtual chains these algorithms no doubt have in store for us. Then again, if they do manage to snare us and this ends up on the menu, we’ll pray for a mercifully quick end to the suffering.

The idea is pretty simple; the clock’s face is an empty pizza pan that fills with pretend pizza as the day builds to noon, whereupon pizza is removed until midnight when the whole thing starts again. The pizza images are generated by a two-stage algorithm using Stable Diffusion 1.5, and tend to favor suspiciously uncooked whole basil sprigs along with weird pepperoni slices and Dali-esque globs of cheese. Everything runs on a Raspberry Pi Zero W, with the results displayed on a 4″ diameter LCD with an HDMI adapter. Alternatively, you can just hit the web app and have a pizza clock on your desktop. If pizza isn’t your thing, fear not — other food and non-food images are possible, limited only by Stable Diffusion’s apparently quite limited imagination.

As clocks go, this one is pretty unique. But we’re used to seeing unusual clocks around here, from another food-centric timepiece to a clock that knits.

No Crystal Earpiece? No Problem!

January 17, 2025 by 11 Comments

A staple of starting off in electronics ion years past was the crystal set radio, an extremely simple AM radio receiver with little more than a tuned circuit and a point contact diode as its components. Point contact diodes have become difficult to find but can be replaced with a cats whisker type detector, but what about listening to the resulting audio? These circuits require a very high impedance headphone, which was often supplied by a piezoelectric crystal earpiece. [Tsbrownie] takes a moment to build a replacement for this increasingly hard to find part.

It shouldn’t have come as a surprise, but we were still slightly taken aback to discover that inside these earpieces lies the ubiquitous piezoelectric buzzer element. Thus given a 3D-printed shell to replace the one on the original, it’s a relatively simple task to twist up a set of wires and solder them on. The result is given a test, and found to perform just as well as the real thing, in fact a little louder.

In one sense this is such a simple job, but in another it opens up something non-obvious for anyone who needs a high impedance earpiece. The days of the crystal radios and rudimentary transistor hearing aids these parts were once the main target for may both have passed, but just in case there’s any need for one elsewhere, now we can fill it. Take a look at the video, below the break.

Fancy trying a crystal radio? We’ve got you covered.

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A Direct Conversion Receiver Anyone Can Build

January 15, 2025 by 28 Comments

A couple of years ago one of the Hackaday Prize finalists was a project to take highschoolers through building a direct conversion radio receiver for the 40 metre amateur band. It was originated by the SolderSmoke podcast, and we’re pleased to see that they’ve recently put up an overview video taking the viewer through the whole project in detail.

It’s a modular design, with all the constituent building blocks broken out into separate boards on which the circuitry is built Manhattan style. Direct conversion receivers are pretty simple, so that leaves us with only four modules for oscillator, bandpass filter, mixer, and audio amplifier. We particularly like that it’s permeability tuned using a brass screw and an inductor, to make up for the once-ubiquitous variable capacitors now being largely a thing of the past.

A point that resonated was that most radio amateurs never make something like this. Arguments can be made about off-the-shelf rigs and chequebook amateurs, but we’d like to suggest that everyone can benefit from a feel for analogue circuitry even if they rarely have a need for a little receiver like this one. We like this radio, and we hope you will too after seeing the video below the break.

Need reminding? See the Hackaday.io project page, and the Hackaday Prize finalists from that year.

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