On the left side of the image, three lit candles are positioned next to each other, so that the flames merge. On the right side, an oscilloscope screen is shown displaying an oscillating waveform.

2025 One Hertz Challenge: A Flaming Oscillator And A New Take On The Candle Clock

August 17, 2025 by 6 Comments

Candle clocks were once an easy way to build a clock without using complex mechanical devices: just observe how quickly a thin candle burns down, mark an identical candle with periodic gradations, and you had a simple timer. These were the first candle-based timekeeping devices, but as [Tim]’s flicker-based oscillator demonstrates, they’re certainly not the only way to keep time with a flame.

Generally speaking, modern candles minimize flickering by using a wick that’s designed to balance the amount of wax and air drawn into the flame. However, when several candles are brought close together, their flames begin to interfere with each other, causing them to flicker in synchrony. The frequency of flickering is a function of gravity and flame diameter alone, so a bundle of three candles will flicker at a fairly constant frequency; in [Tim]’s case, it was about 9.9 Hz.

To sense this oscillation, [Tim] originally used a phototransistor to detect the flame’s light, but he wanted an even simpler solution. He positioned a wire just above the flame, so that as it flickered it would periodically contact the wire. A flame has a different dielectric constant than air does, so the capacitance between this and another wire wrapped around the bundle of candles fluctuates with the flame. To sense this, he used a CH32V003 microcontroller, which reads capacitance, performs some signal processing to get a clean signal, counts oscillations, and uses this time signal to blink an LED once a second. The final result is unusually mesmerizing for a blinking LED.

In something of the reverse of this project, we’ve also seen an oscillator used for an (artificial) candle. There’s also a surprising amount of science that can be learned by studying candles.

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2025 One Hertz Challenge: Digital Clock Built With Analog Timer

August 13, 2025 by 1 Comment

You can use a microcontroller to build a clock. After all, a clock is just something that counts the passage of time. The only problem is that microcontrollers can’t track time very accurately. They need some kind of external timing source that doesn’t drift as much as the microcontroller’s primary clock oscillator. To that end, [Josh] wanted to try using a rather famous IC with his Arduino to build a viable timepiece.

[Josh]’s idea was straightforward—employ a 555 timer IC to generate a square wave at 1 Hz. He set up an Arduino Uno to count the pulses using edge detection. This allowed for a reliable count which would serve as the timebase for a simple 24-hour clock. The time was then displayed on an OLED display attached over I2C, while raw pulses from the 555 were counted on a 7-segment display as a useful debugging measure. Setting the time is easy, with a few pushbuttons hooked up to the Arduino for this purpose.

[Josh] claims a drift of “only ~0.5 seconds” but does not state over what time period this drift occurs. In any case, 555s are not really used for timekeeping purposes in this way, because timers based on resistor-capacitor circuits tend to drift a lot and are highly susceptible to temperature changes. However, [Josh] could easily turn this into a highly accurate clock merely by replacing the 555 square wave input with a 1PPS clock source from another type of timer or GPS device.

We’ve had quite a few clocks entered into the One Hertz Competition already, including this hilariously easy Nixie clock build. You’ve got until August 19 to get your own entry in, so wow us with your project that does something once a second!

2025 Hackaday One Hertz Challenge

Building A 7-Segment Shadow Clock

August 10, 2025 by 6 Comments

There are plenty of conventional timepieces out there in the world; we’ve also featured a great many that are aesthetically beautiful while being unreadably esoteric. This neat “shadow clock” from [Smart Solutions for Home] is not conventional, but it’s still a clock you could use every day.

The display is made of four seven-segment digits, which have a subtle appearance. Each segment uses a solenoid to extend it forward out of the display, or to retract it flush with the faceplate. This creates a numerical display in all one color, with the physical protrusion doing the job of making the numbers visible. This is perhaps where the “shadow clock” name comes from, though you notice the protruding segments moreso than the shadows they cast on the faceplate.

Running the show is an ESP32, paired with H-bridges to drive the solenoids that make up the 7-segment displays. The H-bridges are driven via shift registers to reduce the number of GPIO pins needed. Unlike many other ESP32 clock builds, this one uses a DS3231 real-time clock module to keep accurate time, rather than solely relying on Internet-based NTP time servers. Configuring the clock can be done via a web interface. Design files are available online.

If you think you’ve seen this recently, maybe you’re thinkig of this prototype for a very similar display by [indoorgeek]. And that’s not the only way to make shadow clocks either. After all, the term is not enforced or defined by any global horological organization. Maybe that’s a good thing! Video after the break.

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Clock Of Clocks Expands, Goes Digital

August 8, 2025 by 9 Comments

Some people just want to have their cake and eat it too, but very few of us ever get to pull it off. [Erich Styger] has, though with V5 of his “MetaMetaClock”— a clock made of clocks, that uses the orientation of the hands to create digits.

We’ve seen previous versions of this clock. As before, the build is exquisitely detailed and all relevant files are on GitHub. This version keeps the acrylic light-pipe hands of version 4, but adds more of them: 60 clocks vs 24. Larger PCBs are used, grouping the dual-shaft steppers into groups of four, instead of the individual PCBs used before. Each PCB has an NXP LPC845 (a Cortex M0 microcontroller) that communicates on an RS-485 bus. Placing four steppers per microcontroller reduces parts count somewhat compared to previous versions (which had each ‘clock’ on its own modular PCB) albeit at the cost of some flexibility.

While the last version used veneers on its face, this version is cut by CNC by from a large slab of oak. It’s certainly the most attractive version yet, and while bigger isn’t always better, more clock faces means more potential effects. Date? Time? Block letters? Arbitrary text? Kaleidoscopic colours from the RGB LEDs? It’s all there, and since it’s open source, anyone who builds one can add more options. A BLE interface makes it quick and easy to wirelessly switch between them or set the time.

It’s nice sometimes to watch projects like this improve incrementally over time. [Erich] mentions that he plans to add Wifi and a web-based user interface for the next version. We look forward to it, and are grateful to  [jicasi] for the tip. Just as it is always clock time at Hackaday, so you can always toss a tip of your own into the box.

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2025 One Hertz Challenge: The Real-Time Clock The VIC-20 Never Had

August 8, 2025 by 6 Comments

Like many early microcomputers, the Commodore VIC-20 did not come with an interna real-time clock built into the system. [David Hunter] has seen fit to rectify that with an add-on module as his entry to the 2025 One Hertz Challenge.

[David]’s project was inspired by a product that Hayes produced in the 1980s, which provided a serial-port based real-time clock solution for computers that lacked one on board. The heart of the project is an Arduino Uno, which itself uses a Dallas DS3231 RTC module to keep accurate time. [David] then drew from an IEC driver developed by [Lars Pontoppidan] for the MM2IEC project. This enables the Arduino to report the time to the VIC-20 via its IEC port.

The project is a neat way to provide a real-time clock source to programs written in Commodore BASIC. It’s also perfectly compatible with the IEC bus, so it can be daisy chained along with printers and disk drives without issue. [David] hasn’t tested it with a Commodore 64, but he suspects it should work just as well on that platform, too.

If you’ve ever wanted to build something clock-based for the VIC-20 but didn’t know how, this is a great piece of hardware to solve that problem. Meanwhile, you might find joy in reading about real-time clock hacks for other systems like the Raspberry Pi. Meanwhile, if you’re working on your own nifty timekeeping projects, don’t hesitate to let us know!

2025 Hackaday One Hertz Challenge

2025 One Hertz Challenge: The Easy Way To Make A Nixie Tube Clock

August 7, 2025 by 3 Comments

Let’s say you want to build a Nixie clock. You could go out and find some tubes, source a good power supply design, start whipping up a PCB, and working on a custom enclosure. Or, you could skip all that, and just follow [Simon]’s example instead.

The trick to building a Nixie clock fast is quite simple — just get yourself a frequency counter that uses Nixie tubes for the display. [Simon] sourced a great example from American Machine and Foundry, also known as AMF, the company most commonly associated with America’s love of bowling.

The frequency counter does one thing, it counts the number of pulses in a second. Thus, if you squirt the right number of pulses to represent the time — say, 173118 pulses to represent 5:31 PM and 18 seconds — the frequency counter effectively becomes a clock. To achieve this, [Simon] just hooked an ESP32 up to the frequency counter and programmed it to get the current time from an NTP time server. It then spits out a certain number of pulses every second corresponding to the current time. The frequency counter displays the count… and there you have your Nixie clock!

It’s quick, dirty, and effective, and a sweet entry to our 2025 One Hertz Challenge. We’ve had some other great entries, too, like this nifty hexadecimal Unix clock, and even some non-horological projects, too!

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Some renderings of shapes made from lines including triangles and a circle.

2025 One Hertz Challenge: Analog Clock For Microsoft Windows

August 4, 2025 by No comments

Our hacker [glgorman] sent in their submission for the One Hertz Challenge: an analog software clock for Microsoft Windows.

I guess we’d have to say that this particular project is a work-in-progress. There is no final clock, yet. But a number of yak’s have been shaved. For instance, we have code for computing geometric objects without using branch instructions, including points and lines and circles and such.

The notes dive deep into various rabbit holes. At one point we find ourselves computing the angle to the sun in the sky, that we may be able to cast the shadow of the clock hands on our clock face. The notes include miscellaneous source code snippets and various screenshots of geometric renderings which have been achieved so far.

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