2025 One Hertz Challenge: Abstract Aircraft Sculpture Based On Lighting Regulations

August 12, 2025 by Lewin Day 5 Comments

The 2025 One Hertz Challenge is really heating up with all kinds of projects that do something once every second. [The Baiko] has given us a rather abstract entry that looks like a plane…if you squint at it under the right conditions.

It’s actually quite an amusing abstract build. If you’ve ever seen planes flying in the night sky, you’ve probably noticed they all have similar lights. Navigation lights, or position lights as they are known, consist of a red light on the left side and a green light on the right side. [The Baiko] assembled two such LEDs on a small sliver of glass along with an ATtiny85 microcontroller.

Powered by a coin cell, they effectively create a abstract representation of a plane in the night sky, paired with a flashing strobe that meets the requirements of the contest. [The Baiko] isn’t exactly sure of the total power draw, but notes it must be low given the circuit has run for weeks on a 30 mAh coin cell.

It’s an amusing piece of PCB art, though from at least one angle, it does appear the red LED might be on the wrong side to meet FAA regulations. Speculate on that in the comments.

In any case, we’ve had a few flashers submitted to the competition thus far, and you’ve got until August 19 to get your own entry in!

2025 One Hertz Challenge: Using Industrial Relays To Make A Flasher

August 10, 2025 by Lewin Day 8 Comments

These days, if you want to flash some LEDs, you’d probably grab a microcontroller. Maybe you’d go a little more old-school, and grab a 555. However, [Jacob] is even more hardcore than that, as evidenced by this chunky electromechanical flasher build.

[Jacob] goes into great detail on his ancillary write-up, describing how the simple building blocks used by industrial control engineers can be used to make a flasher circuit that cycles once per second. Basically, two relays are paired with two 0.5-second delay timers. The two relays tag each other on and off on delay as their timers start and expire, with the lamp turned on and off in turn.

We’ve had lots of other great entries to our One Hertz Challenge, too — from clocks to not-clocks. There’s still time to get an entry in — the deadline for submission is Tuesday, August 19 at 9:00AM Pacific time. Good luck out there!

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

August 8, 2025 by Lewin Day 5 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 One Hertz Challenge: The Easy Way To Make A Nixie Tube Clock

August 7, 2025 by Lewin Day 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!

Continue reading “2025 One Hertz Challenge: The Easy Way To Make A Nixie Tube Clock” →

2025 One Hertz Challenge: An Animated Ferrofluid Display

August 6, 2025 by Lewin Day 12 Comments

Ferrofluid is fun. You’ve probably seen all kinds of demos with it bouncing around in response to magnetic fields, or dancing near a speaker. [beastie417] decided to turn the entertaining fluid into a display.

The basic concept of the ferrofluid display. Note the header image of this article shows the electromagnet array without the ferrofluid pane in place.

The concept is straightforward enough. First, construct a tank of ferrofluid with a white panel behind it for contrast. Then, place it in front of a grid of electromagnets. Now you have many “pixels” you can turn on and off. You turn a magnet on to attract ferrofluid to that point, and turn it off to let it fall away. Since the ferrofluid contrasts with the white background, you have a viable display!

[beastie417] notes that while the concept is simple, the execution is hard. Ferrofluid can be very difficult to work with, instantly staining many materials like acrylic and even glass that isn’t properly prepared. It can also be quite expensive to construct a display like this, with [beastie417] noting their 16×12 pixel design costing approximately $700 thus far. Then you have to figure out how to drive all the pixels—this project uses DRV8908 coil driver ICs running off a microcontroller which controls the display and handles animations.

We’ve seen some great ferrofluid displays before, like this neat build that could even create readable glyphs. Meanwhile, if you’re doing rad things with the coolest fluid of the new millennium, don’t hesitate to let us know!

2025 One Hertz Challenge: 4-Function Frequency Counter

July 31, 2025 by Lewin Day 1 Comment

Frequency! It’s an important thing to measure, which is why [Jacques Pelletier] built a frequency counter some time ago. The four-function unit is humble, capable, and also an entry into our 2025 One Hertz Challenge!

The build began “a long while ago when electronic parts were still available in local stores,” notes Jacques, dating the project somewhat. The manner of construction, too, is thoroughly old-school. The project case and the sweet red digits are both classic, but so is what’s inside. The counter is based around 4553 BCD counter chips and 4511 decoder ICs. Laced together, the logic both counts frequency in binary-coded decimal and then converts that into the right set of signals to drive the 7-segment displays. Sample time is either 1 Hz or 0.1 Hz, which is derived from an 8MHz oscillator. It can act as a frequency meter, period meter, chronometer, or a basic counter. The whole build is all raw logic chips, there are no microprocessors or microcontrollers involved.

It just goes to show, you can build plenty of useful things without relying on code and RAM and all that nonsense. You just need some CMOS chips and a bucket of smarts to get the job done!

A sine wave and triangle wave on a black background

2025 One Hertz Challenge: Op-Amp Madness

July 31, 2025 by Adam Zeloof 7 Comments

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.