Measuring The Accuracy Of A Rubidium Standard

A rubidium standard, or rubidium atomic clock, is a high accuracy frequency and time standard, usually accurate to within a few parts in 1011. This is still several orders of magnitude less than some of the more accurate standards – for example the NIST-F1 has an uncertainty of 5×10-16 (It is expected to neither gain nor lose a second in nearly 100 million years) and the more recent NIST-F2 has an uncertainty of 1×10-16 (It is expected to neither gain nor lose a second in nearly 300 million years). But the Rb standard is comparatively inexpensive, compact, and widely used in TV stations, Mobile phone base stations and GPS systems and is considered as a secondary standard.

[Max Carter] recently came into possession of just such a unit – a Lucent RFG-M-RB that was earlier in use at a mobile phone base station for many years. Obviously, he was interested in finding out if it was really as accurate as it was supposed to be, and built a broadcast-frequency based precision frequency comparator which used a stepper motor to characterise drift.

Compare with WWVB Broadcast

WWVB Receiver
WWVB Receiver

The obvious way of checking would be to use another source with a higher accuracy, such as a caesium clock and do a phase comparison. Since that was not possible, he decided to use NIST’s time/frequency service, broadcasting on 60 kHz – WWVB. He did this because almost 30 years ago, he had built a receiver for WWVB which had since been running continuously in a corner of his shop, with only a minor adjustment since it was built.

Comparator Circuit Installed in a Case

His idea was to count and accumulate the phase ‘slips’ generated by comparing the output of the WWVB receiver with the output of the Rb standard using a digital phase comparator. The accuracy of the standard would be calculated as the derivative of N (number of slips) over time. The circuit is a quadrature mixer: it subtracts the frequency of one input from the other and outputs the difference frequency. The phase information is conveyed in the duty cycle of the pulses coming from the two phase comparators. The pulses are integrated and converted to digital logic level by low-pass filter/Schmitt trigger circuits. The quadrature-phased outputs are connected to the stepper motor driver which converts logic level inputs to bi-directional currents in the motor windings. The logic circuit is bread-boarded and along with the motor driver, housed in a computer hard drive enclosure which already had the power supply available.

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Odd Clock Moves Minute Hand to Hour Hand

We see a lot of clocks here on Hackaday. Some make it easy to tell the time, others are more cryptic. [dragonator] has done something that is so simple, we are surprised it isn’t more common. In a typical mechanical hand clock the minute and hour hands rotate around the same axis. [dragonator] decided to take the minute hand and move it out to the tip of the hour hand.

It works because of a gear system hidden behind the thick hour hand. As the hour hand turns, the gear system rotates, the last gear of which is connected to the minute hand. Since the minute hand rotates 12 times for every one revolution of the hour hand, the gear ratio can easily be calculated.

hand in hand clockThe 3D printed parts were designed by [dragonator] himself. All of the design files are available here for anyone who wants to build one of these neat clocks.

The clock uses a Trinket microcontroller board to keep track of the time and to send step signals to a StepStick that drives a NEMA 17 stepper motor. There is no on-board battery power for this clock, 9-12vdc comes in via a wall wart and is stepped down to 5v by the micro controller’s regulator. Even still, this is a great project that makes it fun to watch time pass, check the video out after the break.

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Large Seven-Segment Clock Build Takes Time To Perfect

[Kevin Rye] built a discrete TTL based seven-segment clock, and he wasn’t too happy with the ugly insides compared to the nice enclosure he built for it. He embarked on creating another large seven-segment clock to put inside that enclosure.

Clocks, and specifically seven-segment based ones, aren’t anything new to write about. This particular project, which is still work in progress, is interesting. [Kevin] is an experienced hacker, but the problems he encountered and resolved along the way could prove useful to a fellow hacker someday.

To start with, he tried rectifying his old build. But in his own words “You can polish a turd, but it’s still a turd.” Five years later, he’d had enough. He’s built a lot of other clocks, but rather than repurposing them, he decided to start from scratch. He quickly breadboarded an Arduino, some displays and drove them using the Multiplex7seg library. That library supports only four characters, so he was back to the drawing board. With a fresh start, his design is now moving along nicely. For now, he’s designed three boards for the display, two boards for the colons between digits, the main Arduino-clone controller board and a 3D printed front frame to hold the displays. It will be nice to finally see that enclosure receive some fitting occupants and bring this build to closure.

Fibonacci Clock Is Hard To Read, Looks Good

Artists have been incorporating the golden ratio in their work for many hundreds of years, and it is thought that when proportions are in line with this ratio, it tends to be more aesthetically pleasing. With that in mind, the clock that [Philippe] created must mathematically be the best looking clock we’ve ever featured, even if it is somewhat difficult to tell time from it.

The clock is made up of squares which represent the first five numbers of the Fibonacci sequence. The squares are backlit with LEDs, which will illuminate red for the hour, green for the minute, and blue representing the overlap of hours and minutes. Simply add up the red and blue squares to get the hour, and add the green and blue squares to get the minutes. The minutes are displayed in 5 minute increments since there aren’t enough blocks though, so you’ll also have to multiply. Confused yet? If not, it turns out that there are several ways to display certain times using this method, any of which can be randomly selected by the clock. [Philippe] reports that there are 16 different ways to represent 6:30, for example.

The clock is driven by an ATmega328P and is housed in a wooden case. There are schematics and code available on [Philippe]’s site if you want to build your own, there are detailed descriptions of how to tell time with this clock. You’ll probably need those. If you like getting confused by clocks, you might also like this one as well.

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Building A Transistor Clock From Scrap

[Phil] has already built a few clocks with Nixies, VFDs, and LED matrices. When his son requested his own clock, he wanted to do something a little different. Inspired by the dead bug style of [Jim Williams]’ creations, [Phil] set out to build a clock made entirely out of discrete components. That includes the counters, driver circuits, and an array of LED.

There are a few inspiration pieces for [Phil]’s clock, starting with the Transistor Clock, a mains-powered clock that uses 194 transistors, 566 diodes, and exactly zero integrated circuits. Design patterns from a clock so beautiful it’s simply called The Clock are also seen, as is a Dekatron emulator from [VK2ZAY].

[Phil]’s creation has no PCB, and all the components are soldered onto tiny wires arranged into something resembling the clocks circuit. It’s a fantastic contraption, and while we’ll still have to give the design award to the clock, [Phil]’s creation shows off the functional circuits; great if he’ll ever need to debug anything.

An RGB Word Clock, Courtesy Of WS2812s

A word clock – a clock that tells the time with illuminated letters, and not numbers – has become standard DIY electronics fare; if you have a soldering iron, it’s just what you should build. For [Chris]’ word clock build, he decided to build an RGB word clock.

A lot has changed since the great wordclock tsunami a few years back. Back then, we didn’t have a whole lot of ARM dev boards, and everyone’s grandmother wasn’t using WS2812 RGB LED strips to outshine the sun. [Chris] is making the best of what’s available to him and using a Teensy 3.1, the incredible OctoWS2812 library and DMA to drive a few dozen LEDs tucked behind a laser cut stencil of words.

The result is blinding, but the circuit is simple – just a level shifter and a big enough power supply to drive the LEDs. The mechanical portion of the build is a little trickier, with light inevitably leaking out of the enclosure and a few sheets of paper working just enough to diffuse the light. Still, it’s a great project and a great way to revisit a classic project.

Strapping an Apple II to Your Body

Now that the Apple wristwatch is on its way, some people are clamoring with excitement and anticipation. Rather than wait around for the commercial product, Instructables user [Aleator777] decided to build his own wearable Apple watch. His is a bit different though. Rather than look sleek with all kinds of modern features, he decided to build a watch based on the 37-year-old Apple II.

The most obvious thing you’ll notice about this creation is the case. It really does look like something that would have been created in the 70’s or 80’s. The rectangular shape combined with the faded beige plastic case really sells the vintage electronic look. It’s only missing wood paneling. The case also includes the old rainbow-colored Apple logo and a huge (by today’s standards) control knob on the side. The case was designed on a computer and 3D printed. The .stl files are available in the Instructable.

This watch runs on a Teensy 3.1, so it’s a bit faster than its 1977 counterpart. The screen is a 1.8″ TFT LCD display that appears to only be using the color green. This gives the vintage monochromatic look and really sells the 70’s vibe. There is also a SOMO II sound module and speaker to allow audio feedback. The watch does tell time but unfortunately does not run BASIC. The project is open source though, so if you’re up to the challenge then by all means add some more functionality.

As silly as this project is, it really helps to show how far technology has come since the Apple II. In 1977 a wristwatch like this one would have been the stuff of science fiction. In 2015 a single person can build this at their kitchen table using parts ordered from the Internet and a 3D printer. We can’t wait to see what kinds of things people will be making in another 35 years.

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