Put A Little Pigeon In Your Next Clock Project

If you’re anything like us, you’ve probably wondered why gear teeth are shaped the way they’re shaped. But we’ll go out on a limb and say you’ve never wondered why gear teeth aren’t shaped like pigeons, and what a clock that’s not quite a clock based around them would look like.

If this sounds like it has [Uri Tuchman] written all over it, give yourself a cookie. [Uri] has a thing for pigeons, and they make an appearance in nearly all his whimsical builds, from his ink-dipping machine to his intricately engraved metal mouse. For this build, pigeons are transformed into the teeth of a large, ornate wheel, cut from brass using an impressive Friedrich Deckel pantograph engraver. To put the pigeon wheel to work, [Uri] built an escapement and a somewhat crooked pendulum, plus a drive weight and dial. It’s almost a clock, but not quite, since it doesn’t measure time in any familiar units, and the dial has a leg rather than hands — classic [Uri].

It may not be [Clickspring]-level stuff, but it’s still a lovely piece of work, and instructive to boot. The way [Uri] figured out the profile for the meshing teeth by looking at the negative space swept out by the pigeon profiles was pretty sweet. Plus, pigeons.

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An Apple ][ With A Pendulum

Clocks are a favourite project here, and we can say we’ve seen all conceivable types over the years. Just a software clock on a retrocomputer perhaps isn’t the coolest among them, but [Willem van der Jagt ]’s Apple][ clock has a little bit extra. It takes its time reference from a real pendulum, on an antique wall clock.

A proximity sensor next to a metal pendulum gives an easy way to generate a digital pulse on each pass, but leaves the question of how to transfer it to the computer. With computers of this age the circuitry is surprisingly simple, and in this case he’s sending an interrupt to the machine which the software can pick up for its timing. There is a small logic circuit between the sensor and the interrupt allowing him to gate the pendulum line, triggered from one of the output lines exposed on the Apple’s game port.

The code is written in assembly, and counts the number of pendulum swings before incrementing the number of minutes. It’s an enjoyable reminder of the days when the architecture of a computer was this accessible, and for those of us whose past lies in the Sinclair world it’s also been a little peek into something of how the Apple works.

We think this is the first pendulum-driven retrocomputer clock we’ve seen here at Hackaday, as you might understand when a clock has a pendulum it’s usually a more traditional design.

Clock Runs Computer In Slow-Motion

At the heart of all computers is a clock, a dedicated timepiece ensuring that all of the parts of the computer are synchronized and can work together to execute the instructions that the computer receives. Clock speeds for most modern off-the-shelf computers and smartphones operate around a billion cycles per second, and even clocks that tick at a human-dizzying speed of a million times per second have been around since at least the 1970s. But there’s no reason a computer can’t run at a much slower speed, as [Greg] demonstrates in this video where he slows down a 6502 processor to a single clock cycle per second.

To reduce the clock speed from the megahertz range down to a single hertz or single clock cycle per second, [Greg] is using the pendulum from an actual clock. He attaches a small magnet to the bottom of the pendulum which is counted by a sensor as it swings past. Feeding that pulse into a monostable conditioner yields a clock signal which is usable for one of his 6502-based computers, and at this extremely slow rate, it’s possible to see the operation of a lot of the computers’ inner workings a step at a time. In fact, he optimized the computer’s operation as this slow speed let him see some inefficiencies in the program he was running.

It helps if your processor is static, of course. Older CPUs with dynamic storage for registers and some with limited-range PLLs would not work with this technique. The 8080A, for example, required a clock of at least 500 kHz.

Not only can this computer use a pendulum clock as the basis for its internal clock, but [Greg] also rigged up a mechanism to use a heartbeat. Getting in a little bit of exercise to increase his heart rate first will noticeably increase the computer’s speed. And, if you’re looking to get a deeper glimpse into the inner workings of a computer, we’d recommend looking at one which forgoes transistors in favor of relays.

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An Atomic Pendulum Clock Accurate Enough For CERN

That big grandfather clock in the library might be an impressive piece of mechanical ingenuity, and an even better example of fine cabinetry, but we’d expect that the accuracy of a pendulum timepiece would be limited to a sizable fraction of a minute per day. Unless, of course, you work at CERN and built  “the most accurate pendulum clock on the planet.”

While we’re in no position to judge [Daniel Valuch]’s claim, we’re certainly inclined to believe him, mainly because the 1950s-era Czechoslovakian pendulum clock his project was based on, the Elektročas HH3, was built specifically as a master clock for labs, power plants, and broadcast use. The pendulum of this mid-century beauty is made of the alloy invar, selected for its exceptionally low coefficient of thermal expansion. This ensures the pendulum doesn’t change length with temperature, but it still only brings the clock into the 0.1 second/day range.

Clearly that’s not good enough for a clock at CERN, the European Laboratory for Nuclear Research, where [Daniel] works as an RF engineer. With access to a 10-MHz timebase from a cesium fountain atomic clock — no less a clock than the one that’s used to define the SI second, by the way — [Daniel] looked for ways to sync the clock up to it. Now, we know what you’re thinking — he must have used some kind of PLL to give an electromagnetic “kick” to the bob to trim the pendulum’s period. Good guess on the PLL, but the trimming method is a little cruder — [Daniel] uses a stepper motor attached to the clock’s frame to pay out or retract a length of fine chain into a cardboard dish attached to the pendulum’s rod. The change in mass changes the pendulum’s center of gravity, which changes its effective length, and allows the clock to be tuned a couple of seconds per day.

It seems like [Daniel] is claiming that his chain-corrected clock won’t drift more than a second from the cesium clock for 158 million years. Again, we’ll take his word for it, but it’s a wonderfully ad hoc approach to tuning the clock, and we appreciate its simplicity.

Building Reaction Wheels With Python And LEGO

Reaction wheels are useful things, typically used by satellites to keep themselves oriented the right way up in space. Turning the reaction wheel creates an equal and opposite torque in the spacecraft, allowing it to point and rotate itself accurately. The same technique also works here on Earth, and [Brick Experiment Channel] decided to build one out of LEGO to control an inverted pendulum.

The initial design using a small LEGO wheel on an inverted pendulum was only able to work reliably over a 4-degree angle from the vertical. Upgrading the wheel to a larger, heavier one enabled the wheel to instead work over a 28-degree range instead.

A MPU9250 inertial measurement unit was pressed into service for control of the reaction wheel, fitted to the base of the pendulum and read by a Raspberry Pi. The Pi takes accelerometer and gyroscope readings, and then controls the motor on the pendulum with a PID controller to keep the inverted pendulum upright.

The video goes into a great deal of detail on what it takes to make the pendulum run smoothly. From changes to the control coefficients to measuring the motor’s back EMF, [Brick Experiment Channel] demonstrates everything required to make the pendulum robust to outside perturbances.

The inverted pendulum is a great way to learn about control theory, as we’ve seen time and again.

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PendulumSynth Ties Music And Physics Together

Many musicians will be familiar with the metronome, a pendulum charged with generating a rhythmic tick to keep one’s performance in regular time. With PendulumSynth, [mrezanvari] takes the same basic pendulum but uses it in an altogether different musical way.

The build relies on a 10-inch plastic ball to serve as the weighted end of the pendulum, stuffed with a STM32F411CE BlackPill board, a BNO085 IMU, and an nRF radio module for sending out data for external processing. The pendulum’s motion is turned into MIDI data or CV for output to musical hardware which handles actually generating the output sounds.

The system operates in a variety of modes. Gravity mode outputs continuous MIDI data and CV relative to the continuous motion of the pendulum, while DIV3 mode tracks the pendulum’s motion and outputs 3 regular trigger points that correspond as such.

The combination of the intuitive physical nature of the pendulum and its sheer large size makes for an enticing musical exhibit. We’ve seen some other great musical installation pieces before, too. Video after the break.

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This POV Clock Combines A Nixie With A Pendulum

Talk about your mixed timekeeping metaphors: there are clocks, and pendulum clocks, and there are Nixie clocks, and persistence of vision clocks. But this is a Nixie pendulum POV clock, and we think it’s pretty cool.

We first spied this on Twitter and were subsequently pleased to learn that [Jayzon Oeve] has posted a more detailed build log over on Hackaday.io. Rather than a moving array of dots to create the characters to display, this uses a single IN-12b Nixie tube at the end of a pendulum. The pendulum is kept moving by a small nudge created by a pulse through a fixed hard drive voice coil acting on a magnet affixed to the bottom of the pendulum — we’ve seen a similar approach used before.

Pretty much all of the electronics are mounted on the pendulum arm, including a Nano, an RTC, and an accelerometer to figure out where in the swing the bob is and when to flash a number on the display. There’s a video below that shows it at work both at full speed and in slow-motion; as always with POV clocks, these things probably look better in person than on video. And while swinging Nixies around like that seems a little dicey, we like the way this turned out.

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