Once per second. That sounds almost insultingly easy. Your microwave manages it. Your wall clock manages it. The little blinking colon on a digital alarm clock has been doing it for decades without demanding applause. Yet the 2025 Hackaday One Hertz Challenge proved that asking hardware hackers to make something happen at exactlyor approximatelyone hertz can open a surprisingly deep rabbit hole of electronics, mechanics, physics, software optimization, and beautifully unnecessary engineering.
Launched by Hackaday on June 26, 2025, the challenge invited makers to build a device in which something happened once every second. Entrants had until August 19, 2025, and the contest ultimately attracted 115 submitted projects. The top three projects each earned a $150 DigiKey shopping prize. More importantly for the rest of us, the competition produced a wonderfully strange catalog of clocks, oscillators, relays, GPS references, vacuum tubes, flames, radioactive decay experiments, microcontrollers, and devices that seemed determined to avoid solving a simple problem in a simple way.
What Was the 2025 Hackaday One Hertz Challenge?
The official rule was refreshingly compact: build something that does something once per second. How that one-second rhythm was generated was intentionally left open. A project could blink an LED, move a mechanism, produce a sound, update a display, count pulses, or perform some other observable action.
Accuracy mattered only as much as the builder wanted it to matter. One maker could pursue a laboratory-grade timing reference while another could construct an electromechanical contraption that wandered around one hertz like a distracted dog on a long leash. Both approaches captured the point of the competition.
Hackaday even created honorable-mention themes that encouraged different interpretations. Timelords rewarded obsession with precision. Ridiculous celebrated wonderfully impractical ways of generating a once-per-second event. Clockwork focused on timepieces and visible mechanisms. And Could Have Used a 555 acknowledged the elephant in every electronics workshop: yes, a humble 555 timer can make a roughly one-hertz oscillator, but where is the fun in stopping there?
Why One Hertz Is More Interesting Than It Looks
A hertz is simply one cycle per second, so 1 Hz sounds like kindergarten-level frequency generation. In practice, the phrase “once per second” immediately raises several engineering questions.
How Long Is a Second, Exactly?
For an ordinary LED flasher, being a few milliseconds early or late barely matters. For precision timekeeping, the definition becomes much less casual. The SI second is defined using the cesium-133 atom: specifically, 9,192,631,770 periods associated with its ground-state hyperfine transition.
That gigantic number makes the challenge’s humble 1 Hz target feel rather different. A one-second output can be the final result of dividing an extraordinarily stable high-frequency reference billions of timesor it can be the result of charging a capacitor until a transistor decides that enough is enough.
Frequency Stability Quickly Becomes the Real Challenge
A basic resistance-capacitance oscillator can produce a one-hertz signal with very few parts. A 555 timer operating in astable mode is the classic example: its oscillation frequency depends primarily on resistor and capacitor values. DigiKey even provides calculators for designing these timer circuits.
But components are imperfect. Capacitors have tolerances. Resistors change slightly with temperature. Supply voltage and circuit construction can influence behavior. What looks like a perfect one-second flash during a ten-second bench test might accumulate noticeable error after running for hours or days.
Watch crystals provide another familiar solution. A 32.768 kHz crystal is popular because 32,768 equals 215, allowing binary divider stages to reduce the signal neatly toward one pulse per second. Even crystals, however, can drift because of temperature, aging, loading, and manufacturing tolerance. Microchip has noted that a typical 20 ppm watch crystal can translate to tens of seconds of timing error per month without calibration.
The Challenge Produced Far More Than Blinking LEDs
The most entertaining aspect of the 2025 Hackaday One Hertz Challenge was the range of solutions. Giving 100-plus hardware hackers the same basic frequency target did not result in 100 copies of the same timer circuit. It produced something closer to an electronics zoo.
The Electromechanicalanalogdigitalclock
The judges’ top selection was Christian’s marvelously named Electromechanicalanalogdigitalclock. Its title sounds like somebody accidentally merged three product descriptions, but that confusion was part of its charm.
The project used a mains-powered stepper motor and a photochopper to derive a 1 Hz signal. That pulse drove CMOS counting logic, with a digital-to-analog conversion stage eventually controlling vintage moving-coil meters to display time. A brass framework and spring-mounted motor added a dose of mechanical sculpture to the electronic design.
It was not merely a clock. It was an exhibition of different generations of technology cooperating under one roofand occasionally sounding as though they might be arguing.
BEZICRON Turned Hair Bands Into a Clock Display
The second winning project, BEZICRON by ekaggrat singh kalsi, took an entirely different approach. Its display used flexible hair bands manipulated by cams and mechanical linkages to form changing numerals.
Instead of another seven-segment LED display, the numbers physically emerged from moving elastic material. The mechanism combined clockmaking, kinetic art, fabrication, and the kind of idea most people would dismiss approximately three seconds before a Hackaday reader says, “Wait, that might actually work.”
A one-hertz pulse animated the clock’s colon, giving the mechanical display a rhythmic heartbeat.
A Candle Flame Became a Time Base
Perhaps the most conceptually delightful winner came from Tim, who experimented with oscillations in candle flames. Instead of treating the flickering flame as random noise, the project investigated its recurring behavior and extracted a useful timing signal.
A wire interacting with the flame fed a capacitive sensing arrangement connected to a microcontroller. The resulting oscillation could be measured and processed until a 1 Hz output was produced.
This is exactly the sort of project that explains why a seemingly narrow maker challenge works so well. Nobody actually needs a candle-powered electronic timing reference. That is also precisely why someone needed to build one.
Some of the Best 1 Hz Engineering Experiments
The winners were only a small part of the story. Many entries explored completely different interpretations of one-second timing.
An STM32 Blinking in Under 50 Bytes
One project attacked perhaps the oldest microcontroller exercise imaginable: Blink. Rudra Lad optimized a blinking program for an STM32F4 Discovery board until the compiled binary occupied fewer than 50 bytes and required no RAM.
From a practical perspective, modern microcontrollers usually provide vastly more memory than an LED blinker requires. From an educational perspective, however, ruthless optimization forces the programmer to understand startup code, registers, instruction encoding, compiler behavior, and hardware timing rather than hiding everything behind convenient libraries.
Making an LED blink is beginner territory. Making it blink with almost nothing is an entirely different sport.
Industrial Relays Made a Delightfully Chunky Flasher
Another entry ignored microcontrollers entirely and constructed a flasher from industrial relays and timing modules. Two relays worked with half-second delay timers, alternately triggering each other and switching a lamp.
Could one integrated circuit have replaced most of the hardware? Absolutely. Would the integrated circuit produce satisfying mechanical clicks every half-second? Absolutely not.
The project highlighted an important maker lesson: engineering competitions do not always reward the smallest bill of materials. Sometimes the mechanism itself is the experience.
A Relay Computer Became an Extremely Overqualified Blinker
Peter’s relay-based computer went even further. Instead of using a tiny timing circuit to toggle a lamp, the project recruited a programmable relay CPU capable of substantially more complicated operations.
The system switched a 220-volt lamp at approximately one hertz, with measurements showing rising edges around 1.01 seconds apart. Calling it a blinking-light circuit would be like calling a bulldozer a gardening spoon. Technically, yes. Spiritually, not quite.
Restoring Hardware That Helped Synchronize Time
At the opposite end of the seriousness spectrum was the restoration of an HP 115BR frequency divider associated with historic precision timekeeping equipment. Working alongside the HP 5060A atomic frequency standard, the equipment could take a 100 kHz reference and divide it down toward a highly accurate one-second tick.
The project connected the maker challenge with the history of electronic time standards. The 1 Hz output suddenly was not merely a blinking light; it was the endpoint of an entire measurement chain designed to transform a stable frequency standard into usable time.
GPS Offered the Modern Precision Shortcut
Several projects naturally turned toward GPS. Many GNSS receivers expose a pulse-per-second, or PPS, output synchronized to their timing solution. For experimenters, this creates a remarkably accessible precision reference.
A microcontroller can count, discipline, compare, or display that pulse rather than trying to maintain long-term timing accuracy using its ordinary processor clock alone. The One Hertz Challenge included projects using GPS timing to calibrate clocks and discipline oscillators, demonstrating the enormous gap between merely generating one hertz and generating one hertz that remains trustworthy over time.
What the Challenge Teaches Electronics Makers
The 2025 Hackaday One Hertz Challenge worked because its constraint was understandable to beginners but expandable almost without limit.
Start With the Output, Then Question the Time Base
A beginner might start with an Arduino, toggle an output, wait a second, and toggle it again. Arduino’s own documentation demonstrates simple timed blinking, while non-blocking approaches using millis() allow the processor to perform other work between events.
That immediately leads to better questions. Does the project require a 1 Hz cycle or one pulse every second? Does the output need a 50% duty cycle? How much drift is acceptable? Does it need to remain synchronized with UTC? Should it survive a power failure? Does it need to work for five minutes or five years?
Measure Before Claiming Precision
A stopwatch may be enough to confirm that a novelty gadget is approximately correct. A serious timing project deserves an oscilloscope, logic analyzer, frequency counter, GPS reference, or another trustworthy measurement method.
This was reflected directly in the contest rules: extraordinary accuracy claims required evidence. That is good engineering practice far beyond competitions. “It looks right” and “I measured it” belong to two very different neighborhoods.
Constraints Create Better Projects
The challenge also demonstrated why intentionally artificial restrictions can be educational. Asking somebody simply to “build a clock” encourages familiar solutions. Asking somebody to generate one hertz without silicon, with relays, from fire, with almost no program memory, or with maximum timing accuracy forces the designer to learn something new.
Constraints remove the easiest escape routes. Once the obvious answer disappears, creativity gets called in for overtime.
Why the 2025 Hackaday One Hertz Challenge Stood Out
Modern electronics makes basic timing almost too easy. A microcontroller costing a few dollars can perform millions of operations while maintaining timers, communicating over wireless networks, driving displays, and occasionally remembering to blink an LED.
The One Hertz Challenge temporarily stripped away that complexity and focused attention on one fundamental concept: a repeatable event in time.
From there, makers rebuilt complexity voluntarily.
One second arrived through motors, logic counters, mechanical displays, GPS receivers, ancient frequency dividers, 555 timers, microcontroller instructions, radioactive processes, relay logic, crystals, and even candle flames. The result was less a contest about clocks than a demonstration of how many engineering paths can connect the same starting point and destination.
Practical Builder Experience: What Chasing One Hertz Teaches You
For anyone inspired by the 2025 challenge, attempting a one-hertz project is an excellent bench exercise because the first version can be ridiculously easy while every improvement exposes another engineering layer.
A typical experience begins with confidence. Connect an LED to a microcontroller, write a few lines of code, and make it blink. Congratulations: one hertz has been conquered before the coffee cooled.
Then you connect an oscilloscope.
Now the period is 1.003 seconds. Or perhaps 0.997 seconds. The duty cycle is not exactly symmetrical. Startup introduces a strange first pulse. Adding serial output changes timing slightly. Suddenly the innocent blinking LED has become an interrogation lamp questioning everything you thought you knew about clocks.
Experience One: Simple Timing and Accurate Timing Are Different
The first major lesson is that generating an interval and maintaining a reference are separate problems. Software delays are convenient, but processor clocks have tolerances. RC oscillators are beautifully simple, but component variation and temperature matter. Watch crystals improve stability dramatically, yet they still drift. GPS PPS signals can provide excellent long-term synchronization, but now your supposedly simple blinker needs a receiver, antenna visibility, startup handling, and logic for signal loss.
Every improvement solves one problem while politely placing another problem on the bench.
Experience Two: Watching the Signal Changes the Project
Measurement tools make one-hertz projects surprisingly satisfying. At high frequencies, an oscilloscope trace can feel abstract. At one hertz, you can literally watch individual transitions arrive.
Compare your circuit against a known reference and timing error becomes visible. Let two nominally one-hertz sources run simultaneously and their edges slowly slide apart. That tiny movement explains oscillator drift more effectively than a page full of equations.
A useful experiment is to build two independent sources: perhaps a microcontroller timer and a 555 oscillator. Display both channels together. Adjust the analog oscillator until the edges nearly overlap, then leave everything running. Temperature changes, capacitor tolerance, oscillator stability, and calibration stop being textbook vocabulary and become things you can see.
Experience Three: Mechanical One Hertz Is Much More Dramatic
Electronics can toggle millions of times per second without complaint. Ask a physical mechanism to move every second and suddenly friction, noise, inertia, contact wear, backlash, and power consumption enter the conversation.
That is why relay and mechanical entries are so compelling. A MOSFET switching at 1 Hz is nearly silent. A relay produces a decisive click. A stepper motor visibly advances. A cam rotates. A meter needle moves. Time gains mass.
For beginners, adding a physical output can transform a forgettable breadboard experiment into something memorable. Drive a solenoid, rotate a mechanical counter, move a flag, ring a small bell, or advance a gear train. Just remember that inductive loads require appropriate driver circuitry and protection; microcontroller GPIO pins are brave little creatures, but they should not be asked to wrestle a relay coil directly.
Experience Four: Weird Ideas Often Teach More
The winning candle-flame experiment is a perfect example. Nobody selecting components for a commercial clock would begin the meeting with, “Have we considered fire?” Yet exploring flame oscillation involves sensors, signal conditioning, noise, frequency measurement, physical phenomena, and experimental repeatability.
Likewise, a relay computer blinking a lamp is objectively excessive if the goal is merely illumination. But the project becomes a demonstration of computing architecture and electromechanical logic. An ultra-small STM32 program turns blinking into an exercise in low-level code optimization. A vintage frequency divider turns it into restoration and metrology.
The practical lesson is simple: when building for education, the most efficient solution is not automatically the most valuable one.
Experience Five: Documentation Is Part of Engineering
One of the contest’s smartest requirements was project documentation. Schematics, photographs, measurements, source code, design reasoning, and failure notes allow other builders to reproduce the result rather than merely admire it.
If you build your own one-hertz experiment, record the oscillator source, measured period, expected error, supply voltage, component values, environmental conditions, and measurement equipment. Include what failed. A resistor value chosen incorrectly, a timer overflow misunderstood, or a crystal loaded improperly can be more educational than the polished final circuit.
Good documentation also forces clearer thinking. Nothing exposes a fuzzy design assumption quite like trying to explain it to another person.
Conclusion
The 2025 Hackaday One Hertz Challenge took one of the simplest specifications imaginable and turned it into a celebration of creative engineering. Between June and August 2025, makers submitted 115 projects exploring what could happen once every second, from precision GPS timing and historic atomic-clock hardware to relay computers, tiny STM32 binaries, flexible mechanical displays, 555 experiments, and oscillating candle flames.
The challenge’s real achievement was showing that frequency is not merely a number printed beside an oscilloscope trace. Timing intersects with physics, programming, mechanics, analog electronics, digital logic, measurement, history, and human creativity.
If you want to try the idea yourself, start with an LED blinking once per second. Then make it more accurate. Or less sensible. Replace the microcontroller. Add gears. Synchronize it to GPS. Make it audible. Build it from relays. Measure its drift for a week. Generate the pulse using something nobody would reasonably classify as a clock.
Because once hackers are given a specification as simple as “do something every second,” the only predictable outcome is that somebody will find an impressively complicated way to do it.
Note: The 2025 One Hertz Challenge has ended, and the winners discussed above reflect Hackaday’s official contest results announced in September 2025.
