After building the big clock, he resolved to make a tiny one for his car [above, foreground, and at right]. Through a fellow tube collector, he obtained some small Japanese Nixie tubes and crafted a surface-mounted circuit based on three stacked pc boards. The clock, which measures 80 by 25 by 45 mm, has a built-in dc-dc converter to step the car's 12 V up to the 200 V required by the tubes.

Childhood Fascination

Ralf Spettel, Weilerbach, Germany

As a child, Ralf Spettel was enchanted with a few mysterious glass tubes he kept in a drawer. When he grew older, he found out they were called Nixie tubes, and after a few Web searches, he learned how to make them glow. The next step, of course, was to build a clock. His large radio-controlled clock [right] synchronizes itself with signals from the atomic clock at the Physikalisch-Technische Bundes- anstalt in Braunschweig, Germany.

"I'm usually too lazy to set the correct time," he says—not very convincingly because he was industrious enough to produce an elegant design based on a 90S8515 microcontroller and impeccable circuit boards. In a new version of the clock [not shown], he dispensed with the calendar function and put a smaller versIon of the clock, also radio controlled, in a handsome wood case.

Where in the World?

Katsushi Matsubayahi, Tokyo

The simplest way for an electronic clock to keep time is to count cycles of house current, and that's what many Nixie-tube clocks do. But not Katsushi Matsubayashi's. His receives signals from the U.S. Defense Department's Global Positioning System (GPS) satellites. The orbiters provide the clock with not only submillisecond accuracy but also the date and the clock's latitude, longitude, altitude, speed, and bearing.

Admittedly, the position data aren't much use to Matsubayashi, who keeps his clock in his rather stationary office at the Tokyo National College of Technology, where he is an associate professor of mechanical engineering. But the clock has been a big hit there: "Some teaching colleagues feel nostalgic towards it; some students are surprised at GPS, and get interested in vacuum tubes, which they have never seen before," he writes.

When trying to decide what kind of case to put the clock in, he got sharply differing views from co-workers. "The teaching staff in mechanical engineering suggested that the circuit should be clearly seen from the outside, whereas those in electrical engineering suggested the circuit should not be seen from the outside," Matsubayashi reports. "If gears or motors had been used, their suggestions might have been reversed."

No Transistors Needed

Geoff Tomlin, Ipswich, Suffolk, UK

There are basically two ways to switch the 200 Vdc that light a digit in a Nixie tube. You can use a cheap small-signal transistor, or you can splurge and use a 74141 IC, which has the high-voltage transistors built in. Geoff Tomlin rejected both approaches and opted for an evocative assemblage of rotary switches. As a high school senior in 1969, inspired by an article in an electronics magazine, Tomlin built a clock using military surplus rotary switches to apply the high voltage to the appropriate Nixie digit in sequence. The time reference is a one- revolution- per-minute synchronous motor; gears divide this time reference to turn the hour and minute rotary switches at the proper rates.