Congratulations! You just landed on the official homepage of the world's
first propeller clock using a nixie tube; the name of the device is
Nixie Tube Propeller Clock (or NTPClock for short).
[ Motivation ]
[ Press ]
[ Video ]
[ Hardware ]
[ Firmware ]
[ History ]
[ Resources ]
The #1 question related to this gadget is, of course, why, WHY,
WHY?! Why would anybody want to build such a thing? Well, the answer is
simple: having joined the NEONIXIE-L (>) nixie
enthusiast Yahoo Group as one of the first members, I decided to create
something different. Clocks using nixie tubes (>)
had certainly existed prior to NEONIXIE-L (although the group gave the Nixie
movement a significant amount of boost and structure), so if my contribution
was to be a clock (which I preferred the most, being a devoted clock
freak myself), it had to be an unusual clock of some sort. Rather quickly
the propeller clock (>) design came to mind;
propeller clocks had also existed before [since the mid-90's], but they all
seemed to use a column of LEDs. Building the world's first nixie tube
propeller clock was just too great of an opportunity to pass on.
In essence, this clock is nothing else than the successful combination of
an exotic display method with an exotic display device.
An article about the Nixie Tube Propeller Clock was
published in the February edition of the Circuit Cellar magazine. Click on the
image below to open the article in PDF format.
Note: The article was posted on this website with the permission of
This webpage serves as a complement to the article; it contains details that did not make
the article due to length constraints, or because of the overly specific nature of the information
only relevant to readers who contemplate about reproducing the device themselves. This page is also
where the most recent firmware updates and other clock-related news are posted.
The embedded video below shows the NTPClock in operation. Notice the light-bluish glow from the
left side of the device [right side in the movie]. Yes, you guessed it right: that is the light from
the infrared LED that illuminates the photo diode above the Spinning Board's "index hole" to produce
the stationary display. (This little-known property of near-infrared sensitivity is inherent to the
CCD and CMOS image sensors of digital cameras.)
You will also notice some choppiness and
irregularity in the display, as some of the digits appear to be blank, while the others are on. This
is merely an artifact of the display refresh rate and video frame rate not being completely in sync.
In real life no such choppiness is experienced; while the display does show some slight flickering
[virtually nothing in a dark environment, as the after-image of the comparatively bright nixie will
fill in the blank, literally speaking...], this occurs in all digit positions in unison.
Even if you happen to be browsing away at work, watch the movie with confidence - it's
completely silent. However, if sound is not an issue for you, I recommend watching
the same movie with soundtrack.
The full schematic diagram in PDF format can be viewed by clicking on the
The nixie tube, as well as the entire clock electronics driving it, is
placed on the Spinning Board - the circuit board mounted on the floppy drive's
carousel. The heart of the device is a single Microchip PIC16F84A
microcontroller. (One of the goals of this project was to familiarize myself
with the PIC's, and to see how much computing power can be crammed into this
very popular low-end micro.) Port B of the PIC is dedicated to receiving
signals from the environment, such as the Control button, the 12/24H selector
jumper and the photodiode required to provide a stationary display. The BCD code
output on Port A lights up the digits through the classic 74141
dedicated high-voltage nixie driver chip. (Just like nixie tubes, this chip
has become obsolete as well. However, this part number's Russian equivalent
is still available on the Web; for example, the
of All Spectrum Electronics offers it, together with other related goodies.)
The toughest challenge, as far as the hardware is concerned, was the
generation of the high voltage required to ignite the nixie tube. Fortunately,
multiple solutions exist; one of the most popular genre is a
switching-mode power supply using a single coil to induce the high voltages.
These circuits are typically based on specialized chips, such as the Maxim
MAX771; an even simpler approach uses a plain 555 timer, see Lance
Turner's nixie power supply kit. The solution employed in the NTPClock is
the simplest of all. Most small, battery-operated fluorescent lights (available
in hardware- and variety stores) contain a tiny circuit that produces the high
voltage necessary for their operation; it is based on a relaxation oscillator
connected to a transformer, and can provide enough high-voltage power to drive
a nixie tube. Such a circuitry yanked out from a fluorescent lamp serves as
the NTPClock's barbaric DC-DC converter.
The output of the circuit is one-way rectified and filtered. Since the
voltage of the unloaded output can reach up to 400 V, a Zener
diode is used to cap the nixie's anode voltage to prevent the infamous
ghosting phenomenon from occurring when none of the cathodes are
The power to the entire system is provided by the stationary Power Board.
The 12 V needed for the floppy motor is supplied directly from the 4-way
rectified and filtered [unregulated] 9 V AC input voltage. Since the
floppy electronics also requires 5 V, the Power Board houses the 5 V
regulator as well; this voltage is supplied to the Spinning Board through the
home-made slip ring assembly. (Taking the 12 V DC to the Spinning
Board instead would make it possible to remove the nixie current from the
regulator's load, but it would require a second regulator on the Spinning
Board. Taking the 9 V AC itself would make high voltage generation
easier, but the implementation of the Control button would become a bit
The firmware of the Nixie Tube Propeller Clock was written entirely in
PIC assembly. This made it possible to provide an implementation that
fulfills the timing requirements of the propeller clock functionality, and
also remains within the boundaries of the 16F84's very limited resources. (The
only somewhat pressing issue was the fill-up of the 8-deep hardware
stack whenever the waves collide over the poor micro's head - symbolically
speaking. However, with a little trickery the situation could be
The time is kept and the Control button is read with the help of the
periodic Timer0 overflow interrupts. In Stationary Mode, the display is
stabilized by detecting the photodiode of the Spinning Board's "index hole"
passing over the stationary infrared LED mounted on the floppy drive
electronics. The turn of the carousel is tracked by carefully crafted code
execution delays in the firmware's background code; this is responsible for
generating the "spatially multiplexed" propeller display.
You can download the NTPClock's firmware using the links below:
- The PIC assembly source code
- The machine code in HEX format
Even that odd-ball PIC assembly can be handled by ordinary mortals, but
only if the super counter-intuitive instructions are replaced by a set
of well-designed macros. (This by no means is a criticism of the PIC
assembly language! Some of the instructions are strange because the
microcontroller's architecture itself is unique.) My macro collection below
is intended to make programming in PIC assembly as easy as pic... I mean, pie.
- My collection of useful PIC assembly macros
The new "instructions" were inspired by 68000 and Z80
assembly mnemonics. One important thing to point out is that while the data
transfer macros retained the "destination last" convention suggested by the
original PIC instructions (e.g., "MOVWF"), the comparison macros
follow the "destination first" convention, thus nipping one more source of
counter-intuitivity in the bud.
The nixie tube is one of the most ancient electronic display
technologies, predating the LED, the LCD and other contemporary displays. It
was invented by the 2nd generation Hungarian-American Haydu brothers in
1952, and was marketed by the Burroughs Corporation from 1954. Technically
speaking, the nixie tube is a cold-cathode gas discharge tube, very
similar to ordinary neon bulbs. The difference is that nixie tubes have not
one, but multiple cathodes, crafted in the shape of the supported symbol set.
Connecting a sufficiently high voltage (typically 170 V) between one of the
cathodes and the anode, the desired symbol will light up in a beautiful,
ethereal orange glow.
The name "nixie" comes from the abbreviation "NIXI", referring
to "Numeric Indicator eXperimental No. 1". (Yes, indeed; if only the 9th experiment
were to come out successful, the device would probably be called "NIXIX". :-) ) The
jury is still out whether the word "nixie" needs to be capitalized or not.
During the decades it has become a genericized trademark; because of
this fact, and the decapitalization trends that started at the end of
the last millenium, the lower case version is more and more commonly
The Wikipedia article on nixie
tubes offers a good starting point for further research. Today the
technology is clearly obsolete, but the beautiful appearance of the tubes
themselves and the light they emit will keep drawing in enthusiasm as long as
there is a single working nixie left on Earth...
propeller clock was built by Bob Blick in 1995; it takes advantage of
the phenomenon in visual perception called positive after-images
(formerly known as persistence of vision) to produce a 2-dimensional
display perception from a single column of physically moving LEDs.
Since then the technology has found its way into commercial
devices, such as the Fantazein Message Clock, the Globe Clock
(with caller ID), and a host of other gadgets, typically with message sign
functionality. Another interesting approach is shown by the ROPOD by Seth LaForge; here
rods of LEDs rotated in a plain cover a disk-shaped surface, on which regular
2D images are displayed. The challenge involved is the mapping of the pixels
of the original image to the ROPOD's inherent polar coordinates.
Yahoo! group was founded by crackpot inventor Raymond Weisling (the designer
of the Four Letter Word and GeekKlok electronic surrealities) on
January 27, 2002. As it turned out, Ray had had the idea of creating a
community for hobbyists interested in this unique technology, so he started to prowl
eBay monitoring nixie transactions for a short period of time, and politely
approached the buyers [and maybe even the sellers] with his Yahoo group idea.
I happened to be one of the buyers caught up in Ray's web [no pun intended],
but since my nixie purchase was more of an impulse buying than an acquisition
with a concrete plan behind it, I accepted Ray's invitation only with a bit of
reluctance. I also kept thinking, "This is quite a hare-brained idea; he can't
possibly recruit more than a handful of people, so the whole effort is
probably dead in the water." Boy, was I totally wrong... not only that group
membership exploded within weeks, NEONIXIE-L literally became a
life-altering experience for me: thank to the excellent patrons of the
group, I quickly drank my fair share of Kool-Aid from the nixie glass, and
became a serious nixie-fan myself.
Note: The group's name is the result of the word "nixie" being
prefixed by "neo-" (meaning "new", from the Greek word "neos"), a subtle
reference to the nixie renaissance the group represents. By no means is
it trying to refer to the neon gas found inside all nixie tubes...!
Update: The original NEONIXIE-L Yahoo! group is now closed to new
memberships, and only serves as an archive. It has been replaced by the
Google Group. (As they say in educated circles, "Le Roi est mort, vive le Roi!")
◆ The Nixie Tube Propeller Clock
The first version of the Nixie Tube Propeller Clock was built in the summer
of 2002, and spun out the first complete time/date display on June 27,
2002 at 0:30:52 CDT. This original design had the contacts mounted on
the Spinning Board, while the headphone plug was dropped down from above the board;
the push-button was right underneath the tip of the plug, and could be activated by
gently pushing down on the plug's support structure. (This historical picture of the v1 design
shows the device in its original form. On this second picture the same design can be
seen with a stationary Spinning
Board.) As ingenious as this approach was, it had a couple of mechanical issues,
which prevented the clock from running reliably for an extended period of time. The
gadget needed a serious revision, but as it always happens, I just never had the time
to get around it for four long years! (Regrettably, the same was true about
this very website, to much of the frustration of several people, including myself...)
Then in the summer of 2006 I said enough is enough, confiscated the necessary
time from other [much less fun] activities, and finalized the project; the work also
included cleaning out the firmware and drafting the schematic diagram properly. Since
the revamp, the NTPClock has been chugging and churning without a glitch!
◆ The World's Second
world's second nixie tube propeller clock was built in January 2006
by Jon Stanley (see his excellent "Electronix and More" site
about his vintage equipment and cool projects).
In the aforementioned site, his frustration over the non-existence of the
NTPClock's official website is obvious:
``I was inspired to build this clock after I saw some links
to see "Nebulus, the world's first nixie propeller clock." Unfortunately, by that
time many of the links were dead and I only managed to find a video of the clock.
I never could find any documentation or schematics for the clock, but I assumed
it probably used a microcontroller and some high voltage chips or transistors.
I happened to find some pictures of it buried in the Yahoo group Neonixie-L files
after I built my nixie propeller clock.' '
Hmm... a very good point! But now this website is ready, so
future enthusiasts should have no more problems finding all the necessary information!
(Note: "Nebulus" is my screen name on NEONIXIE-L.)
Q: These nixie-clocks are really cool! Where can I learn more?
A: Dieter's Nixie Tube Linkpage
is your real treasure trove of related links. (Its update seems to be sporadic, but the links are great.)
Start out with admiring the Cathode Corner
and Jeff Thomas' page, and then
continue going down the list to see the goofiest of projects. Once an advanced nixie musketeer, check out
the nixie page of Sphere Research for
some really obscure parts. But this is still just a tiny
subset of what is out there; a simple web-search will reveal scores of other great pages on nixie tubes,
small microcontroller projects, etc.
Q: I got inspired to start my own project. Any pointers?
A: The Web is teeming with resources for electronics enthusiasts; but one website I found
particularly helpful is EEWeb.com. It features a great
collection of articles in a variety of areas within the field, such as analog, digital, embedded, power, and
a lot more. It also offers online calculators and cheat sheets for the different commonly encountered problems.
But if electronics is more than just a hobby for you, also check out the list of conferences and job postings.
Another website I would highly recommend is Schematics.com.
Schematics is the language of electronics; it provides a concise and comprehensive diagrammatic description of a
circuit. Schematics.com allows users to connect and share
designs and ideas in a like-minded community.
Q: I want to become an engineer too, and play with cool gadgets for
life. Any advice?
A: The University of Illinois at
Chicago's College of Engineering, currently under the leadership of my former advisor Dr. Pete Nelson, is my alma mater. I can fully recommend
this college to any budding engineer to get high-quality education in the field. But let's not forget about
the premium location of the campus either, right next to the heart of Chicago! ;-)
Q: Where can I read more about after-images and other visual
A: Michael Bach's page
on optical illusions is the ultimate resource on this topic. However, be warned that this page
is also very addictive; once you land there, forget about doing any work for the rest of the