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Less expensive and easier to build than some other Nixie clocks. Displays seconds, blinking colons, and it sets itself using WiFi!

Nixie tubes are quite popular with electronic hobbyists lately. They are an antique novelty! I am one of the few among us who is old enough to remember when Nixie tubes were state-of-the-art displays back in the 1960s and early 70s. They disappeared almost instantly with the arrival of LED displays!

Most of the Nixie projects I have seen here are expensive and use pre-assembled Nixie tube displays. My objectives in this project were to make it inexpensive and build it from scratch, so that I really knew how everything works! I wanted it to include seconds. I wanted it to include blinking colons. I wanted it to be configurable to a 12 or 24 hour clock. I wanted the finished product to look nice. And I wanted to do all that for about $100. So here is what I ended up with:

I came pretty close to my $100 cost goal. I have listed the prices in the comments on my parts list. They total $110!

We are using the MKR WiFi 1010 for this project, because it has built-in WiFi and a built-in RTC (real-time clock). It provides a self setting clock which gets the time from the Internet. We will talk more about that in Software.

Design & Construction
We need to start with the obvious warning that Nixie tubes run at 170 volts, so care needs to be taken when working with these circuits, as they can give you a nasty shock!

The simplest way of powering 6 Nixie tubes would be to give them each their own BCD to Decimal cathode driver (SN74141 or the Russian equivalent K155ID1). That way the 170 volt anodes could be powered continuously and we would not need to switch the high voltage on and off. However, that involves a lot of wiring and each SN74141 would require 4 Arduino pins as inputs. We don’t have enough pins with the MKR WiFi 1010, so shift registers or something would be needed to control all the SN74141s.

To keep things relatively simple for my clock, I decided to multiplex all the Nixie tubes through a single SN74141. It simplifies the wiring, as all the Nixie tube’s cathode pins can be tied together, i.e. all 6 Nixie tube pin 1s are tied together and connected to the #1 out pin of the SN74141. The required Arduino pins are greatly reduced. We need 4 as inputs to the SN74141 and 6 to select the proper Nixie tube. (Actually, one more is needed to control the blinking colons.)”

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