A photo of the HAT with the LoRa module and relay visible on the top

2025 One Hertz Challenge: LoRaSense RGB Pi HAT

Our hacker [Avi Gupta] has sent in their submission for the One Hertz Challenge: the LoRaSense RGB Pi HAT.

This “HAT” (Hardware Attached to Top) is for any Raspberry Pi with 40-pin header. The core of the build is the custom printed circuit board which houses the components and interconnects. The components include an SHT31 temperature and humidity sensor, an SX1278 LoRa module, and a 10 amp 220 VAC relay. The interconnects include support for UART, I2C, SPI, and WS2812B RGB LED interfaces as well as a stackable header for daisy chaining HATs.

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A DIY Fermenter For Flavorful Brews

Fermentation is a culinary art where tiny organisms transform simple ingredients into complex flavors — but they’re finicky about temperature. To keep his brewing setup at the perfect conditions, [Ken] engineered the Fermenter, a DIY insulated chamber controlled by Home Assistant for precision and remote monitoring.

The Fermenter build starts with an insulated chamber constructed from thick, rigid foam board, foil tape, weather strips, and a clever use of magnets to secure the front and top panels, allowing quick access to monitor the fermentation process. The chamber is divided into two sections: a larger compartment housing the fermentation vessel and a smaller one containing frozen water bottles. A fan, triggered by the system, circulates cool air from the bottle chamber to regulate temperature when things get too warm.

The electronics are powered by an ESP8266 running ESPHome firmware, which exposes its GPIO pins for seamless integration with Home Assistant, an open-source home automation platform. A DS18B20 temperature sensor provides accurate readings from the fermentation chamber, while a relay controls the fan for cooling. By leveraging Home Assistant, [Ken] can monitor and adjust the Fermenter remotely, with the flexibility to integrate additional devices without rewiring. For instance, he added a heater using a heat mat and a smart outlet that operates independently of the ESP8266 but is still controlled via Home Assistant.

Thanks [Ken] for sending us the tip on this ingenious project he’s been brewing. If you’re using Home Assistant in a unique way, be sure to send in your project for us to share. Don’t forget to check out some of the other Home Assistant projects we’ve published over the years. Like a wind gauge, maybe. Or something Fallout-inspired.

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A sine wave and triangle wave on a black background

2025 One Hertz Challenge: Op-Amp Madness

Sometimes, there are too many choices in this world. My benchtop function generator can output a sine, square, or saw wave anywhere from 0.01 Hz up to 60 MHz? Way too many choices. At least, that’s what we suspect [Phil Weasel] was thinking when he built this Analog 1 Hz Sinewave Generator.

Rendering of a PCB
A KiCad rendering of [Phil]’s design
[Phil]’s AWG (which in this case stands for Anything as long as it’s a 1 Hz sine Wave Generator) has another unique feature — it’s built (almost) entirely with op-amps. A lot of op-amps (37, by our count of the initial schematic he posted). His design is similar to a Phased Locked Loop (PLL) and boils down to a triangle wave oscillator. While a 1 Hz triangle wave would absolutely satisfy judges of the One Hertz Challenge, [Phil] had set out to make a sine wave. Using a feedback loop and some shaping/smoothing tricks (and more op-amps), he rounded off the sharp peaks into a nice smooth sine wave.

Sometimes we make things much more complicated than we need to, just to see if we can. This is one of those times. Are there much simpler ways to generate a sine wave? Yes — but not exclusively using op-amps! This entry brings stiff competition to the “Ridiculous” category of the 2025 One Hertz Challenge.

Stephen Hawes operating his LumenPnP

The LumenPnP Pasting Utility: Never Buy Solder Stencils Again?

Over on his YouTube channel the vivacious [Stephen Hawes] tells us that we never need to buy solder stencils again!

A big claim! And he is quick to admit that his printed solder paste isn’t presently quite as precise as solder stencils, but he is reporting good success with his technique so far.

[Stephen] found that he could print PCBs with his fiber laser, populate his boards with his LumenPnP, and reflow with his oven, but… what about paste? [Stephen] tried making stencils, and in his words: “it sucked!” So he asked himself: what if he didn’t need a stencil? He built a Gerber processing, G-code generating, machine-vision implemented… website. The LumenPnP Pasting Utility: https://paste.opulo.io/

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2025 One Hertz Challenge: 555 Timer Gets A Signal From Above

One of the categories we chose for the One Hertz Challenge is “Could Have Used a 555.” What about when you couldn’t have, but did anyway? The 555 is famously easy to use, but not exactly the most accurate timer out there — one “ticking” at 1 Hz will pulse just about once per second (probably to within a millisecond, depending on the rest of the circuit), but when you need more precise timing, the 555 just won’t cut it. Not on its own, anyway.

An Allan deviation plot
Allan Deviation can be a bit confusing, but generally — lower is more accurate

This entry by [burble] shows us how the humble 555 can hold its own in more demanding systems with some help from a GPS receiver. He used the One Pulse per Second (1PPS) output from a GPS module to discipline the 1 Hz output from a 555 by modulating the control voltage with a microcontroller.

Okay, this sounds a bit like baking a cake by buying a cake, scraping all the icing off, then icing it yourself, but what better way to learn how to ice a cake? The GPS-disciplined 555 is way more accurate than a free running one — just check out that Allan Deviation plot. While the accuracy of the standard 555 begins to decrease as oscillator drift dominates, the GPS-disciplined version just keeps getting better (up to a point — it would also eventually begin to increase, if the data were recorded for long enough). Compared to other high-end oscillators though, [burble] describes the project’s accuracy in one word: “Badly.”

That’s okay though — it really is a fantastic investigation into how GPS-disciplined oscillators work, and does a fantastic job illustrating the accuracy of different types of clocks, and some possible sources of error. This project is a great addition to some of the other precision timekeeping projects we’ve seen here at Hackaday, and a very fitting entry to the competition. Think you can do better? Or much, much worse? You’ve got a few weeks left to enter!

Teufel Introduces An Open Source Bluetooth Speaker

There are a ton of Bluetooth speakers on the market. Just about none of them have any user-serviceable components or replacement parts available. When they break, they’re dead and gone, and you buy a new one. [Jonathan Mueller-Boruttau] wrote in to tell us about the latest speaker from Teufel Audio, which aims to break this cycle. It’s a commercial product, but the design files have also been open sourced — giving the community the tools to work with and maintain the hardware themselves.

The project is explained by [Jonathan] and [Erik] of Teufel, who were part of the team behind the development of the MYND speaker. The basic idea was to enable end-user maintenance, because the longer something is functioning and usable, the lower its effective environmental footprint is. “That was why it was very important for us that the MYND be very easy to repair,” Erik explains. “Even users without specialist knowledge can replace the battery no problem.” Thus, when a battery dies, the speaker can live on—versus a regular speaker, where the case, speakers, and electronics would all be thrown in the garbage because of a single dead battery. The case was designed to be easy to open with minimal use of adhesives, while electronic components used inside are all readily available commercial parts.

Indeed, you can even make your own MYND if you’re so inclined. Firmware and hardware design files are available on GitHub under the Creative Commons Attribution-ShareAlike 4.0 International (CC BY-SA 4.0) license for those looking to repair their speakers, or replicate them from the ground up. The company developed its own speaker drivers, but there’s nothing stopping you from using off-the-shelf replacements if so desired.

It’s a strategy we expect few other manufacturers to emulate. Overall, as hackers, it’s easy to appreciate a company making a device that’s easy to repair, rather than one that’s designed to frustrate all attempts made. As our own Jenny List proclaimed in 2021—”You own it, you should be able to fix it!” Sage words, then as now!

Fusing Cheap EBay Find Into A Digital Rangefinder

One of the earliest commercially-successful camera technologies was the rangefinder — a rather mechanically-complex system that allows a photographer to focus by triangulating a subject, often in a dedicated focusing window, and and frame the shot with another window, all without ever actually looking through the lens. Rangefinder photographers will give you any number of reasons why their camera is just better than the others — it’s faster to use, the focusing is more accurate, the camera is lighter — but in today’s era of lightweight mirrorless digitals, all of these arguments sound like vinyl aficionados saying “The sound is just more round, man. Digital recordings are all square.” (This is being written by somebody who shoots with a rangefinder and listens to vinyl).

While there are loads of analog rangefinders floating around eBay, the trouble nowadays is that digital rangefinders are rare, and all but impossible to find for a reasonable price. Rather than complaining on Reddit after getting fed up with the lack of affordable options, [Mr.50mm] decided to do something about it, and build his own digital rangefinder for less than $250.

Part of the problem is that, aside from a few exceptions, the only digital rangefinders have been manufactured by Leica, a German company often touted as the Holy Grail of photography. Whether you agree with the hype or consider them overrated toys, they’re sure expensive. Even in the used market, you’d be hard-pressed to find an older model for less than $2,000, and the newest models can be upwards of $10,000.

Rather than start from scratch, he fused two low-cost and commonly-available cameras into one with some careful surgery and 3D printing. The digital bits came from a Panasonic GF3, a 12 MP camera that can be had for around $120, and the rangefinder system from an old Soviet camera called the Fed 5, which you can get for less than $50 if you’re lucky. The Fed 5 also conveniently worked with Leica Thread Mount (LTM) lenses, a precursor to the modern bayonet-mount lenses, so [Mr.50mm] lifted the lens mounting hardware from it as well.

Even LTM lenses are relatively cheap, as they’re not compatible with modern Leicas. Anyone who’s dabbled in building or repairing cameras will tell you that there’s loads of precision involved. If the image sensor, or film plane, offset is off by the slightest bit, you’ll never achieve a sharp focus — and that’s just one of many aspects that need to be just right. [Mr.50mm]’s attention to detail really paid off, as the sample images (which you can see in the video below) look fantastic. Continue reading “Fusing Cheap EBay Find Into A Digital Rangefinder”