Nixie clock with IN-12B tubes

Description

On an amateur radio fleamarket 2015, I have been able to buy some Russian indicator tubes (Nixie tubes) of type ИН-12Б. Of course something had to be built with the tubes...

A Nixie tube is a cold cathode display for displaying numerals or other information with an orange glow discharge. The tube contains a wire-mesh anode and multiple cathodes, shaped like numerals or other symbols. The tube is filled with a gas at low pressure (neon or argon). The origin Nixie displays were made by a small vacuum tube manufacturer called Haydu Brothers Laboratories (after 1955 as Burroughs Corporation). The abbreviation "Nixie" as trademark was derived by Burroughs from the name of "Numeric Indicator eXperimental No. I". The most common form of Nixie tube has ten cathodes in the shapes of the numerals 0 to 9 (and occasionally a decimal point). Because the numbers and other characters are arranged one behind another, each character appears at a different depth, giving Nixie based displays a distinct appearance. Each cathode can be made to glow in the characteristic neon-orange color by applying high voltage DC at a few milliamperes between a cathode and the anode.

The Russian ИН-12Б (IN-12B) tubes use the number arrangement as back to front, 1 6 2 7 5 0 4 9 8 3 with the 5 being an upside down 2 (and a bottom far left decimal point between the numbers 8 and 3). A another important consideration is the relatively high-voltage circuitry necessary to drive the tube. Old integrated circuits such as the 74141 BCD decoder and driver have long since been out of production and are rarer then the tubes itself. I am a happy owner of 6 pieces 74141 (thanks to Volker B.!), so this driver was used. Three 74HC595 ICs were used as the buffer and shift register for the sequence of numbers. The necessary high voltage (about 180 V) is generated with a switching power supply and the MAX1771CPA in the DIP-8 housing. The RTC chip RV-3029-C2 operates with a relatively high accuracy for the time base of the clock. A further improvement is a DCF77 module (because of noise immunity not in the same housing as the clock). The clock is controlled by the controller ATmega644P-20PU.

The entire watch is not a great thing, but it is nowadays great to see how the indicator tubes glow orange...