Giant nixie clock PDF Print E-mail
Written by Hans Summers   
Saturday, 28 March 2009 08:49

Z568M Nixie Tubes
The Circuit
Java Clock
Radcom articles, Jan and Mar 2002
More Photographs


At the beginning of 2001 I had never heard of nixie tubes. Then I came across Mike's Electric Stuff and saw his Nixie Clock. Almost instantly I fell in love with nixies... then I had the idea of building a nixie clock and this project was the result.

Z568M Nixie Tubes

After some searching on the web I found the nixie tube I wanted. The tube is a type Z568M, that had been manufactured in East Germany. I purchased a set of six from Jan Wuestens. The "New Old Stock" tubes arrived in England in their original cardboard boxes, and plenty of padding and packaging to keep them safe during the journey (well done Jan).

The Z568M is 4-inches high (100mm) and has a digit height of 2 inches (50mm). It is therefore truly a giant amongst nixie tubes, presumably intended for railway clock applications and so on. It is painted red, this was originally done to improve the contrast. There is also a non-coated version available, the Z5680M, but I could not obtain any of these at that time. Since I find the internal construction of nixies very beautiful, I removed the paint using a craft knife. This was a long and tedious process during which I was constantly afraid of breaking the tubes, particularly when excavating the seal at the top of the tube. Nevertheless the end results were worth it.

Here is the data for the Z568M giant nixie tube. Originally all I had was the German version of the datasheet, which I couldn't understand that well. Now I have obtained the English version too. The pins marked "ic" are "internal connections", they should be left unconnected.

The circuit

I used a very similar circuit to Mike's nixie clock. Mine is a 6-digit clock, i.e. has an extra pair of nixies for the seconds. I made a few very minor modifications to Mike's circuit. I moved the seconds hold switch to earlier in the counter chain, because I found that otherwise a full second did not elapse between letting go of the switch and the seconds being incremented. Since my clock display seconds, I also connected the colon nixies to be on continuously. I omitted any form of mains isolation, in the interests of living dangerously (do this at your own risk!). I found a series resistance of 22K to be about right for the Z568M, but they overheated so I replaced them with two 47K resistors in parallel (23.5K). The total cost of the electronic parts for this circuit (excluding the nixies) was under UK £10. Of course, the nixies are very expensive, and the materials for the cabinet.
Click here for a full size circuit diagram


I did not use a printed circuit board (PCB), instead I used my favourite method of construction, which is plain matrix board and wire connections. The circuit is built on three circuit boards. The first holds the rectifier, divide by 50 circuit, seconds counters and seconds driver transistors. The second and third boards hold the counters and drivers for the minutes and hours digit pairs.

The nixies are mounted in pairs on single-sided PCB material. I placed the copper side upwards, and drilled holes to match the nixie base. The nixie pins are pushed through the holes and soldered to wires on the underside. It is probably better to use sockets for the nixies but the Z568M is a very large nixie for which I doubt ordinary sockets are available. It is possible to build your own sockets but  I opted for direct soldering, though this must be done with extreme care not to crack the glass. The central nixie pair (minutes) has two PCB-material pillars which the colon neons are attached to, with their 100K series resistors. The circuit board for each pair is attached behind the nixie tubes at right angles to the nixie boards, using triangular cuts of PCB material.

I used reed switches for the three time setting buttons. These are mounted in front of the nixie digit pairs. Again, care must be exercised not to break the delicate glass of these reed switches. From left to right, the switches set "Fast" advance (50Hz), "Slow" advance (1 Hz) and "Hold" seconds. A small bar magnet about 25mm long is sufficient to operate the switches at a distance of more than 1cm, through the glass cabinet. Using these reed switches is an attractive solution to the switch mounting problem, and avoids any risk of the end user suffering electrification from the high voltages present in the circuit.

The three nixie pair assemblies are screwed onto strips of pine wood which are in turn glued to a pine wood base. I built "feet" for the pine base using a thin pine cross section which was probably intended for picture framing. These materials came from the local hardware shop. On the bottom of the "feet" I stuck red self-adhesive felt for a really professional finish! Underneath the pine wood base are two steel self-tapping screws, which the bar magnet sticks to, so that it isn't lost.

The glass cabinet was made from plates of glass cut to my specification at a local glass shop. The front panel is bevelled. I glued them together using a silicone glass glue/sealant, of a type intended for the construction of fish tanks. This is an incredibly messy and difficult process. The silicone sealant is an unpleasant substance to work with, and hard to remove from the glass when dry.

If you have java enabled on your browser, you will have seen a working simulation of this nixie clock at the top of this page. This uses an excellent java applet called DJClock by Naeem Malik, of Xanasoft. Note: A mouse click on the clock suspends the time, another mouse click will restart it. The digits template for this clock is shown below. This picture was obtained by laboriously photographing the clock from the same position, with different displayed times until I had all the digits 0 to 9. Cut and pasting in an image editor resulted in the template. The embedded comments line is 11:0:84:169:254:339:424:509:594:679:764:849:885

This image is used as the background:

Mike Hungerford did a great job of cleaning up both the digits and background images and kindly sent me his improved files, which you now see here. Thanks Mike! Feel free to take these digits and use them on your own java clock, subject to Naeem's copyright and conditions of course.

RadCom articles

The following articles about Nixie clocks appeared in the January and March editions of Radcom, the journal of the Radio Society of Great Britain (RSGB). The March article mentions and pictures my giant Nixie clock. The images are black and white which keeps the download time down but means the photographs aren't reproduced very well.

If you install Adobe Acrobat, you can read Adobe Acrobat (PDF) version of the articles, which is more easily scaleable for viewing and printing. Experiment with the size settings on the Adobe toolbar.

You can also save the .gif files which make up the pages by right clicking on each scanned page and selecting SaveAs (i.e. click the appropriate article below, wait for the images to load, then SaveAs each page of the article individually).

Whatever Next column, RadCom, Jan and Mar 2002:
"Fashionable 'Valves'", "Nixie tubes: a brief history lesson", and "Positive feedback"' (2 pages)

Click here for PDF (257 K)
Reproduced from RadCom with permission of the RSGB.

More Photographs

A 12-inch (30 cm) ruler is shown in front of one of the photos so that you can see this is quite a sizeable clock. In that photo, the seconds digit increased from 3 to 4 during the exposure of the camera, which is why you see a 3 and 4 superimposed. The glass front panel is bevelled. Glass panels were cut to specification from a local glass shop and glued together with a silicone adhesive/sealer intended for aquarium applications. The small "pills" fixed to the backplate anode of the nixies are "getters", containing a small amount of a material such as barium, which sucks up any residual oxygen in the tube. The feet of the clock base are made from shaped pine strips, with a picture-frame type profile. Red felt is fixed to the bottom of the feet and two self-tapping screws store a bar magnet in place for setting the time.

The seconds nixies were unscrewed for this photograph which shows the soldered connections to the nixie pins. The resistors are 22K, but you can see they are blackened due to overheating. I later replaced each 22K resistor with 2 47K resistors in parallel. The pair of nixies on their board are screwed to the pine base using 4 self-tapping brass screws.


Left: View along the nixies, taken from the seconds end. This shows the depth effect of the different nixie digits, due to their different depth placing in the digit stack.

Middle: A close-up photograph of one of the rightermost nixie showing the number 5. Note the dust on the nixie! This picture shows the internal structure of the Z568M quite well.

Right: Nixie Close-up from above, again showing off the internal structures of the Z568M Nixie.

FAME at last!

Side view Gadget Freak feature!

My nixie clock featured in Electronics Weekly's July 2008 Gadget Freak!

Nixie clock by Jonathan Kelly MW3KGQ

Last Updated on Sunday, 17 April 2011 02:41
© 2009 Hans Summers
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