The last two months have consisted mainly of the stress of exams. Meanwhile I have been working on my next project… A Nixie Clock!

A Nixie Clock is a clock which uses Nixie Tubes as the display (mine were made in 1984 in the USSR). Mike’s Electric Stuff, has a good page on Nixie Clocks, if you want to read more. In fact, I am basing my design on Mike’s design, with some modifications, e.g. making it a 24 hour clock.

The circuit counts mains cycles (50Hz in the UK) and uses that to keep time. While this may not sound like the most accurate method, it is. The grid frequency is controlled such that, over the course of a day, the average frequency is exactly 50Hz to a very high accuracy.

The tubes are powered from a rectified mains signal and are switched with transistors.

Having tested the logic circuit on a breadboard, I am now working on building the full logic and power circuit on strip board. The Nixie Tube control circuits will be on separate PCBs.

Because the circuit is build using mainly mains voltages, it is imperative that I take caution when powering and testing the device. To ensure safety I have:

  • Installed a 3A fuse in the plug (the smallest I had)
  • Installed a 1W fusible resistor in series with the circuit
  • Mounted the board on a block of wood with the traces facing downwards. (This ensures that the board doesn’t slip and short/electrocute me)
  • Been very careful to ensure that the power is off when touching the board.

Hopefully, I will survive this project.

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