frequency counter

34 Articles

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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2025 One Hertz Challenge: 4-Function Frequency Counter

July 31, 2025 by 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!

2025 Hackaday One Hertz Challenge

2025 One-Hertz Challenge: ZX Spectrum Is Now A Z80 Frequency Counter

July 18, 2025 by 1 Comment

The ZX Spectrum is perhaps most fondly remembered as a home computer and a games machine. [Tito] has grabbed the faithful black plastic box and turned it into a frequency counter as an innovative entry to our 2025 One Hertz Challenge.

The code was prepared in assembly using ZASM—a Z80 online assembler. It works in quite a simple manner. The code runs for one second at a time, counting rising edges on the EAR port of the ZX Spectrum. Those edges are added up to determine the frequency in question, and the job is done. [Tito] has tested the code and found it’s capable of reading frequencies up to 20 KHz. Since it runs on a one second period, it’s thus eligible for entry by meeting the requirements of the One Hertz Challenge. Code is available on Github for the curious.

The ZX Spectrum has a clock speed of 3.5 MHz, meaning it’s not exactly the tool of choice if you’re reading faster signals. We’ve seen similar done before. In any case, this project was a great way to exercise assembly coding skills and to bust out some classic Speccy hardware—and that’s always a good time. If you’ve got your own retrocomputer hacks brewing up in the lab, don’t hesitate to let us know!

2025 Hackaday One Hertz Challenge

Korean Multifunction Counter Teardown

July 7, 2024 by 5 Comments

[Thomas Scherrer] likes to tear down old test equipment, and often, we remember the devices he opens up or — at least — we’ve heard of them. However, this time, he’s got a Hung Chang HC-F100 multifunction counter, which is a vintage 1986 instrument that can reach 100 MHz.

Inside, the product is clearly a child of its time period. There’s a transformer for the linear supply, through-hole components, and an Intersil frequency counter on a chip. Everything is easy to get to and large enough to see.

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Upgrade Puts A Lot Of Zeroes On Kit-Built Frequency Counter

December 7, 2023 by No comments

If there’s anything more viscerally pleasing than seeing an eight-digit instrument showing a measurement with all zeroes after the decimal point, we’re not sure what it could. Maybe rolling the odometer over to another 100,000 milestone?

Regardless, getting to such a desirable degree of accuracy isn’t always easy, especially when the instrument in question is a handheld frequency counter that was built from a kit 23 years ago. That’s the target of [Petteri Aimonen]’s accuracy upgrade, specifically by the addition of a custom frequency reference module. The instrument is an ELV FC-500, which for such an old design looks surprisingly modern. Its Achille’s heel in terms of accuracy is the plain crystal oscillator it uses as a frequency standard, which has no temperature compensation and thus drifts by about 0.2 ppm per degree.

For a mains-powered lab instrument, the obvious solution would be an oven-controlled crystal oscillator. Those are prohibitive in terms of space and power for a handheld instrument, so instead a VCTCXO — voltage-controlled, temperature-compensated crystal oscillator — was selected for better stability. Unfortunately, no such oscillators matching the original 4.096-MHz crystal spec could be found; luckily, a 16.384-MHz unit was available for less than €20. All that was required was a couple of flip-flops to divide the signal by four and a bit of a bodge to replace the original frequency standard. A trimmer allows for the initial calibration — the “VC” part — and the tiny PCB tucks inside the case near the battery compartment.

We enjoyed the simplicity of this upgrade — almost as much as we enjoyed seeing all those zeroes. When you know, you know.

Simple STM32 Frequency Meter Handles Up To 30MHz With Ease

September 28, 2023 by 11 Comments

[mircemk] had previously built a frequency counter using an Arduino, with a useful range up to 6 MHz. Now, they’ve implemented a new design on a far more powerful STM32 chip that boosts the measurement range up to a full 30 MHz. That makes it a perfect tool for working with radios in the HF range.

The project is relatively simple to construct, with an STM32F103C6 or C8 development board used as the brains of the operation. It’s paired with old-school LED 7-segment displays for showing the measured frequency. Just one capacitor is used as input circuitry for the microcontroller, which can accept signals from 0.5 to 3V in amplitude. [mircemk] notes that the circuit would be more versatile with a more advanced input circuit to allow it to work with a wider range of signals.

It’s probably not the most accurate frequency counter out there, and you’d probably want to calibrate it using a known-good frequency source once you’ve built it. Regardless, it’s a cheap way to get one on your desk, and a great way to learn about measuring and working with time-varying signals. You might like to take a look at the earlier build from [mircemk] for further inspiration. Video after the break.

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Vintage Digital Frequency Meter Teardown

July 19, 2023 by 4 Comments

You think of digital displays as modern, but the idea isn’t that new. We had clocks, for example, with wheels and flip digits for years. The Racal frequency counter that [Thomas Scherrer] is playing with in the video below has columns of digits with lamps behind them. You just need the right plastic and ten lightbulbs per digit, and you are in business. Easy enough to accomplish in 1962.

Inside the box was surprising. The stack of PC boards looks more like a minicomputer than a piece of test gear. There were a few novel items inside, too, ranging from a glass-encapsulated crystal to an interesting method of selecting the line voltage.

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