Ian’s Page

Recently I have been getting into Nixie Tubes. This is an old display technology that predates the common light emitting diode (L.E.D.) display. Nixie tubes look like old fashioned thermionic valves except they do not have a heater. Rather they are filled with neon gas which gives them their characteristic warm orange glow. They are gas discharge tubes, so while they might look like filaments, they are actually powered from a high voltage source (200 volts with a current limiting resistor) and draw very little current (in the mA range). They are cool to touch in operation.

In the future I plan to build a clock which will be microprocessor controlled. So far a have done the following:

• Bought various tubes over the net. Tubes made in Germany, England, Russia and America. Although the tubes went out of production many decades ago, you can still buy new old stock – tubes that have never been used and are still in their original packaging.
• Built a small switch mode power supply to generate the 200 volts from 12 volts.
• Got samples of various semiconductors I plan to use in the final clock, microprocessors, high voltage shift registers, real time clock ICs, TCO oscillators and miscellaneous other support parts.
• Bought a development board for the micro I picked from PJRC.
• Written some test code to fade the digits on the transitions for a proof of concept.

Here are some pictures of interest:

This is the switch mode power supply. It has an adjustable output and is quite efficient (around 80%). It is based on a MAX1771 DC/DC converter.

Hivac XN11 – I bought quite a few of these as they were only £1 each.

Hivac XN12 – Very similar to the XN11 except the anode mesh is much coarser. I have a few of these also, as they were still £1 each.

These are my favourite and I only have 8 of them as they cost quite a bit more. This is mainly due to size, the digits are 1 inch tall. These tubes will make a nice clock.

Here is an mpeg movie of a Nixie tube being driven by the software I wrote to do the fading effect, sorry for the bad quality but it was taken by a webcam. It was hard to get the right exposure without getting beating between the PWM frequency and the shutter speed of the webcam. From memory the fade is achieved with 50 levels of brightness. I think this will look pretty cool on the clock.

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