A Tuning Fork Clock, With Discrete Logic

[Willem Koopman aka Secretbatcave] was looking at a master clock he has in his collection which was quite a noisy device, but wanted to use the matching solenoid slave clock mechanism he had to hand. Willem is a fan of old-school ‘sector’ clocks, so proceeded to build his ideal time piece — Vibrmatic — exactly the way he wanted. Now, since most time keeping devices utilise a crystal oscillator — which is little more than a lump of vibrating quartz — why not scale it up a bit and use the same principle, except with a metal tuning fork? (some profanity, just to warn you!)

Shock-mounted tuning force oscillator

A crystal oscillator operates in a simple manner; you put some electrical energy in, it resonates at its natural frequency, you sense that resonance, and feed it back into it to keep it sustaining. With a tuning fork oscillator, the vibration forcing and the feedback are both done via induction, coils act as the bridge between the electronic and mechanical worlds.

By mounting the tuning fork onto a shock mounting, the 257 Hz drone was kept from leaking out into the case and disturbing the household. This fork was specified to be 256 Hz, but [Willem] reckons the drag of the electromagnets pushed it off frequency a bit. Which make sense, since its a mechanical system, that has extra forces acting upon it.

The sector face was CNC cut from aluminium, the graphics engraved, then polished up a bit. Finally after a spot of paint, it looks pretty smart. Some nice chunks of upcycled wood taken from some building work spoils formed the exposed enclosure. On the electronics side, after totally ignoring the frequency error, and then tripping over a bunch of problems such as harmonics in the oscillation, and an incorrectly set-up divider, a solution which seemed to work was found, but like always, there are quite a few more details to the story to be found in the build log.

We’ve seen a tuning fork clock recently, like this 440 Hz device by [Kris Slyka] that the project above references, and whilst we’re talking about tuning forks, here’s a project log showing the insides of those ubiquitous 32.768 kHz crystal units.

Tuning Fork Keeps This Throwback Digital Clock Ticking

Whatever kind of clock you’re interested in building, you’re going to need to build an oscillator of some sort. Whether it be a pendulum, a balance wheel, or the atomic transitions of cesium or rubidium, something needs to go back and forth in a predictable way to form the timebase of the clock. And while it might not make the best timepiece in the world, a tuning fork certainly fits the bill and makes for a pretty interesting clock build.

One of the nice things about this build is that [Kris Slyka] got their inspiration from a tuning fork clock that we covered a while back — we love it when someone takes a cool concept and makes it their own. While both clocks use a 440 Hz tuning fork — that’s an A above middle C for the musically inclined — [Kris] changed up the excitation method for their build. She used a pair of off-the-shelf inductors, placed near the ends of each arm and bridged by a strong neodymium magnet to both sense the 440-Hz vibrations and to provide the kick needed to keep the fork vibrating.

As for the aesthetic of the build, we think [Kris] really nailed it. Using through-hole components, old-school seven-segment displays, and a home-etched PCB, she was able to capture a retro look that really works. The RS-232 port and the bell jar enclosure complete the feel, although we’re not sure about the custom character set [Kris] designed — it’s cool and all, but makes it hard for anyone else to read without a little practice. Regardless, this is a fun build, and we’d imagine the continuous tone coming from the clock is pretty pleasing.

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Impractical Clock Uses Tuning Fork

Clock projects are so common that they are almost a cliche. After all, microcontrollers have some clock source and are good at counting, so it stands to reason that a clock is an obvious project. [WilkoL’s] clock though has a most unusual clock source: a 440 Hz tuning fork.

A cheap plastic dome really shows off the fork and contributes to this good-looking build. An ATTiny13 divides the input frequency down, handles the display, and obeys the adjustment buttons. It does require a little metalworking, as the tuning fork needed filing and threading, although we bet you could figure out other ways to mount it.

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