2025 One Hertz Contest

3 Articles

A hand holding the foxhunt transmitter

2025 One Hertz Challenge: Ham Radio Foxhunt Transmitter

July 13, 2025 by 8 Comments

[Jim Matthews] submitted his Ham Radio foxhunt transmitter project for the 2025 One Hertz Challenge.

This is a clever Spartan build. In order to create a radio beacon for use in a “fox hunt” [Jim] combined a SR-T300 walkie talkie module with a phototransistor and oscillating LED circuit. The phototransistor and oscillating LED are secured face-to-face inside heat shrink tubing which isolates them from ambient light. When the LED flashes on the phototransistor powers the radio which transmits a tone in the UHF band.

A fox hunt is a game played by radio enthusiasts in which players use radio signals to triangulate and find a hidden beacon. [Jim]’s circuit is the beacon, and when it’s powered by a three volt CR2032 battery, it transmits a strong signal over several hundred yards at 433.5 MHz, within the amateur radio UHF band.

If you’re interested in radio beacons you might like to read about the WSPR beacon.

2025 Hackaday One Hertz Challenge

2025 One Hertz Challenge: An Ancient Transistor Counts The Seconds

July 12, 2025 by 8 Comments

If you’ve worked with germanium transistors, you’ll know that many of them have a disappointingly low maximum frequency of operation. This has more to do with some of the popular ones dating from the earliest years of the transistor age than it does to germanium being inherently a low frequency semiconductor, but it’s fair to say you won’t be using an OC71 in a high frequency RF application. It’s clear that [Ken Yap]’s project is taking no chances though, because he’s using a vintage germanium transistor at a very low frequency — 1 Hz, to be exact.

The circuit is a simple enough phase shift oscillator that flashes a white LED, in which a two transistor amplifier feeds back on itself through an RC phase shift network. The germanium part is a CV7001, while the other transistor is more modern but still pretty old these days silicon part, a BC109. The phase shift network has a higher value resistor than you might expect at 1.8 MOhms, because of the low frequency of operation. Power meanwhile comes from a pair of AA cells.

We like this project not least for its use of very period passive components and stripboard to accompany the vintage semiconductor parts. Perhaps it won’t met atomic standards for timing, but that’s hardly the point.

This project is an entry in the 2025 One Hertz Challenge. Why not enter your own second-accurate project?

2025 Hackaday One Hertz Challenge

Limitations, Creativity, And Challenges

June 28, 2025 by 6 Comments

This week, we announced the winners for the previous Pet Hacks contest and rang in our new contest: The One Hertz Challenge. So that’s got me in a contesty mood, and I thought I’d share a little bit of soap-box philosophizing and inside baseball all at once.

The trick to creating a good contest theme, at least for the creative Hackaday crowd, is putting on the right limitation. Maybe you have to fit the circuit within a square-inch, power it only with a coin cell, or use the antiquated and nearly useless 555 timer IC. (Yes, that was a joke!)

There are two basic reactions when you try to constrain a hacker. Some instantly try to break out of the constraint, and their minds starts to fly in all of the directions that lead out of the box, and oftentimes, something cool comes out of it. The other type accepts the constraint and dives in deep to work within it, meditating deeply on all the possibilities that lie within the 555.

Of course, we try to accommodate both modes, and the jury is still out as to which ends up better in the end. For the Coin Cell challenge, for instance, we had a coin-cell-powered spot welder and car jumpstarter, but we also had some cool circuits that would run nearly forever on a single battery; working against and with the constraints.

Which type of hacker are you? (And while we’re still in the mood, what contest themes would you like to see for 2026?)

This article is part of the Hackaday.com newsletter, delivered every seven days for each of the last 200+ weeks. It also includes our favorite articles from the last seven days that you can see on the web version of the newsletter. Want this type of article to hit your inbox every Friday morning? You should sign up!