Nixie Clock Version 2

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This is the new and improved nixie clock using one of the smallest nixies in the world, the Russian IN-17 nixies. The clock circuit is based on revisions of the version 1 nixie clock that were used in my Single Meter Clock. The logic circuits of the clock is basically identical to the Single Meter Clock except it has SLOW and FAST set instead of hours and minutes set.

Click here for the schematic diagram of my nixie clock.

The only things that is unique to this version 2 clock compared to the version 1 is the 4081 quad 2-input AND chip, which eliminates the 4013 flip flop and the two 4017 counters. An AND gate is wired as a flip flop for the 10 hours, and when set, the "1" digit is lit. A transistor NOT gate is used for the "0" digit on the hours so when the AND gate is reset, the "0" is lit. When the AND gate is set, the transistor is activated, which shuts off the Vcc from the HV transistor so the "0" turns off while the "1" comes on. The other AND gate was used to compare when the hours rolls over to 13 (from 12:59) to reset everything back to 1. The remaining AND gates were used as buffers, one for the 60Hz line and another for the reset circuit.

As a result of using the 4081 chip, I was able to stuff all of the logics and parts on a 3 by 4 inch board. All the ICs were DIP style, all the resistors are rated 1/4W, and the nixie drivers were done the old-fashioned way with MPSA42 HV transistors. The IN-17 nixies only need roughly 130V to light up so it was not necessary to use a voltage doubler off the 120V mains; I used a simple half-wave DC power supply that rectifies the 120VAC mains to roughly 170VDC, and I used a 1uF 200V capacitor for the filtering. The small size filter capacitor serves two purposes: so I could fit it on the packed space on the board and to provide less DC filtering so the nixies flicker slightly. As a result, the life of the nixies are longer because they are not lit continuously. A small neon bulb was inserted between the two pairs of IN-17 nixies as the colon indicator.