# Why Pendulums Sync Up, And Other Mysteries Explained

If you’ve ever seen fireflies flashing together at night, you’ve witnessed the glory of synchronisation. In a new video, [Veritasium] examines some of the mechanisms in nature that help create order out of chaos.

The story begins back in 1665, when [Christiaan Huygens] discovered that two pendulum clocks hanging from the same wooden beam would spontaneously synchronise over a period of time. The same principle is then demonstrated with metronomes – an experiment readily recreated in the home. Other systems that show this same eerie coordiation are then explored – from tidally locked moons orbiting around planets (like ours!), to chemical oscillators discovered by Soviet scientists during the cold war. There’s also a great explanation of the problems faced by the London Millennium Bridge, which swayed wildly under heavy foot traffic as it induced pedestrians to walk in sync.

Overall, it’s a look at some of the action behind the scenes that ties seemingly independent systems together. Learning about such things can prove useful too – it might even help you solve real world problems in your machine shop! Video after the break.

# A Discrete Logic Word Clock

Self-acclaimed computer nerd [Kevin Koster] was tired of designing new TTL-logic clocks before finishing his previous designs. So he finally buckled down and completed this unique word clock, which uses only a handful of TTL chips. We can’t disagree with his friends who complained that they can’t read [Kev]’s handwriting, so perhaps this diagram will make it clearer.

Besides being a nice logic-only project, this will give an example to younger folks how much effort went into things which are so simple to implement today. We don’t see a Karnaugh map on the project page for sorting out the logic diodes driving the minutes LEDs. If [Kev] did it on the fly, as the rat’s nest of diodes on the schematic would suggest, we’re not sure whether to scold him or be impressed (he does redraw that logic very neatly on a separate sheet).

No worries about high speed wiring on this project. The main oscillator derives time from the 50 Hz AC transformer power supply, and outputs a reference clock signal of 16.7 mHz (not MHz), or once per minute. This is divided down to 3.3 mHz for the 5-minutes counter and again to 277 uHz for the hour counter. If you live in a 60 Hz power mains country, you’d have to modify the oscillator section. Or you could contact [Kev] on his site, as he is considering making this available as a kit worldwide. If you like word clocks, we’ve covered quite a few of them before, including this crazy-complex rear-projection one.

# A Soyuz Space Clock Replica

If you like the retro look of old Soviet space hardware, then this replica of the model 774H Soyuz digital clock by [David Whitty] might be the perfect accessory for your desk. Forgoing the original stack of ten jam-packed circuit boards, [David] used an Arduino, a GPS receiver, and a handful of other common parts to create a convincing reproduction.

He also made some functional changes to make it better suited as an ordinary clock for us earthbound folk. If you want to take on this project yourself, be prepared for some real metalwork. No 3D printing filament was harmed in building this project. It’s based on a pair of heavily modified Hammond cast aluminum enclosures, with over 1 kg of lead ballast added to give it the appropriate heft of the original. The GPS patch antenna is cleverly hidden on the rear interface connector, but a discrete hole for a USB connector gives away the secret that this isn’t an original. The software (free for non-commercial use) and build notes are available on his GitHub repository.

We covered [Ken Shirriff]’s fascinating dive into the guts of a real Soyuz digital clock back in January. If old space hardware is your thing, you should definitely check out this teardown by [CuriousMarc] of the 653B, the 1960s-era electro-mechanical predecessor to the 774H. Thanks to [CuriousMarc] for bringing this project to our attention.

# Choosing The Right RTC For Your Project

When it comes to measuring time on microcontrollers, there’s plenty of ways to go about things. For most quick and dirty purposes, such as debounce delays or other wait states, merely counting away a few cycles of the main clock will serve the purpose.  Accurate to the tens of milliseconds, they get the average utility jobs done without too much fuss.

However, many projects are far more exacting in their requirements. When you’re building a clock, or a datalogger, or anything that relies on a stable sense of passing time for more than a few minutes, you’ll want a Real Time Clock. So called due to their nature of dealing with real time, as we humans tend to conceive it, these devices take it upon themselves to provide timekeeping services with a high degree of accuracy. We’ve compiled a guide to common parts and their potential applications so you can get things right the first time, every time.

# Hackaday Podcast 037: Two Flavors Of Robot Dog, Hacks That Start As Fitness Trackers, Clocks That Wound Themselves, And Helicopter Chainsaws

Hackaday Editors Mike Szczys and Elliot Williams take a look at the latest hacks from the past week. We keep seeing awesome stuff and find ourselves wanting to buy cheap welders, thermal camera sensors, and CNC parts. There was a meeting of the dog-shaped robots at ICRA and at least one of them has super-fluid movements. We dish on 3D printed meat, locking up the smartphones, asynchronous C routines, and synchronized clocks.

# Keeping Clocks On Time, The Swiss Way

Could there be a worse fate for a guy with a Swiss accent than to be subjected to a clock that’s seconds or even – horrors! – minutes off the correct time? Indeed not, which is why [The Guy With the Swiss Accent] went to great lengths to keep his IKEA radio-controlled clock on track.

For those who haven’t seen any of [Andreas Spiess]’ YouTube videos, you’ll know that he pokes a bit of fun at Swiss stereotypes such as precision and punctuality. But really, having a clock that’s supposed to synchronize to one of the many longwave radio atomic clocks sprinkled around the globe and yet fails to do so is irksome to even the least chrono-obsessive personality. His IKEA clock is supposed to read signals from station DCF77 in Germany, but even the sensitive receivers in such clocks can be defeated by subterranean locales such as [Andreas]’ shop. His solution was to provide a local version of DCF77 using a Raspberry Pi and code that sends modulated time signals to a GPIO pin. The pin is connected to a ferrite rod antenna, which of course means that the Pi is being turned into a radio transmitter and hence is probably violating the law. But as [Andreas] points out, if the power is kept low enough, the emissions will only ever be received by nearby clocks.

With his clock now safely synced to an NTP server via the tiny radio station, [Andreas] can get back to work on his other projects, such as work-hardening copper wire for antennas with a Harley, or a nuclear apocalypse-Tweeting Geiger counter.

# Hacklet 18 – Tick Tock, It’s Time For Clocks

In three words, Hackers love clocks. Not only do we think that digital watches are still a pretty neat idea, we love all manner of timepieces. This episode of The Hacklet focuses on the clock projects we’ve found over on Hackaday.io.

We start with [rawe] and [tabascoeye], who both put the famous XKCD “now” clock into hardware. [tabascoeye] used a stepper motor in his xkcd world clock. [rawe] didn’t have any steppers handy, so he grabbed a cheap wall clock from Ikea for his xkcd.com/now clock in hardware. The now clock needs a 24 hour movement. Ikea only sells 12 hour movements, so [rawe] hacked in a 555 and some logic to divide the clock’s crystal by two. He’s currently using an EEVblog uCurrent to verify his modified clockwork consumes about half a milliwatt.

Next up is [Craig Bonsignore] and his Touchscreen Alarm Clock. [Craig] got sick of store-bought alarm clocks, so he built his own. Then he modified it, added a few features, and kept building! The current incarnation of the clock has a pretty novel interface: a touchscreen over a bicolor LED matrix. The rest of the clock consists of an Arduino, an Adafruit Wave shield, and a Macetech Chronodot. [Craig] is currently mashing up these open source designs and building a single Arduino shield for his clock.

[Warren Janssens] took the minimalist route with The Iris Clock. Iris is a ring of WS2812 RGB LEDs. The LEDs are mounted behind a wall colored piece of wood in such a way that you can only see their glow on the clock frame and the wall beyond it. This helps a with the eye searing effect WS2812s can have when viewed directly – even when dimmed with PWM. The code is mainly C with some AVR assembly thrown in to control the LEDs. [Warren] has given Iris 8 different time modes, from hour/minute/second to percentage of day with sunrise and sunset markers. With so many modes, the only hard part is knowing how to read the time Iris is displaying!

[David Hopkins] also built a ring clock. His Stargate LED Clock not only tells time, but is a great replica of the Stargate from the TV series. [David] used four Adafruit WS2812 Neopixel segments to build a full 60 RGB LED ring. The Stargate runs on an Arduino nano with a real-time clock chip to keep accurate time. A photoresistor allows the Stargate to automatically dim at night. With some slick programming [David] added everything from a visual hourly “chime” to a smooth fade from LED to LED.

[dehne1] gives us something completely different with The Bendulum Clock. A bendulum is [dehne1’s] own creation consisting of an inverted pendulum built without a pivot. The inverted pendulum swings by bending along its length. In [dehne1’s] design, the bendulum is made out of a spring steel strip rescued from a car windshield wiper. The Bendulum doesn’t have a mechanical escapement, but an electromagnet sensed and driven by an Arduino. The amazing part of this project is that  [dehne1] isn’t using a real-time clock chip. The standard 8MHz Arduino resonator is calibrated over various temperatures, then used to calibrate the bendulum itself. The result is a clock that can be accurate within 1 minute each day. [dehne1] mounted his clock inside a custom wood case. We think it looks great, and want one for Hackaday HQ!

We’ve used enough clock ticks for this episode of The Hacklet. As always, see you next week. Same hack time, same hack channel, bringing you the best of Hackaday.io!

Still want more? Check out our Timepiece List!