Like many other people that have seen nixie tubes I got drawn towards wanting to have my own nixie tube clock. Prices on tubes, sockets, transformers and everything else is pretty steep due to their rarity on the exotic tubes and demand.
I found a home made Volt meter on a HAM flea market containing four Phillips ZM1020 tubes, five sockets, driver ICs and a transformer. This was the basis for building my own nixie clock. I had to buy two additional Mullard ZM1020 off of Ebay and got a sixth socket for free from a user on a Danish HAM site.
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There are many kits available, but prices are high enough for me to make my own circuit design and PCB layout.
Clock frequency can be derived in a few different ways.
- Internal crystal oscillator with dividers
- Micro controller
- Live wire 50/60Hz frequency with dividers
- Radio controlled
I chose to get my 1Hz signal from the live wire powering my clock, this was simply made with 7490 ICs to divide the 50Hz sine wave to a 1Hz square wave.
For powering the tubes it is needed to have around 200 – 300 Volt, easiest way is to just rectify the input voltage but this leaves us with no isolation from the wall socket.Using a transformer is safe and reliable, but it takes up a lot of space. Switch more power supplies can be a lot of work and prove to be a bigger project that the clock itself. I went with the transformer as I already had it salvaged from the Volt meter.
Transformer input: 230VAC
Transformer output: 10VAC and 200VAC
Nixie tubes: Phillips and Mullard ZM1020
D2 half wave rectifies the 50Hz 10VAC for driving Q1, this gives a 50Hz square wave for the input on U2 that divides by five, the new 10Hz signal is fed to U3 that divides by 10 and a 1Hz clock frequency is obtained.
U4 to U9 are counters and depending on which digit it will pass on a signal to the next counter and resets are set backwards.
16th September 2010
Bought a home made Volt meter with tubes, sockets, ICs and transformer
10th December 2010
Circuit design and PCB layout is complete, PCB is etched and drilled.
16th December 2010
Assembling of the PCB with components and sockets is complete. Two minor faults was made in the PCB tracing, was fixable by drilling new holes for a couple of jumpers to make the right connections.
7th January 2011
The enclosure is entirely made from 8 mm acrylic salvaged from LCD monitors. The white squares on the surface originally made for diffusing the background light adds a nice finish.
All pieces for the enclosure is finished and final assembly can begin
12th January 2011
The nixie tube clock is put together
The enclosure turned out much bigger than I first imagined when I set out on building this clock, it is mostly due to the large transformer and the fact that fitting 6 digits that each are 33 mm wide will take up some space.
Setting the time can be a little tricky as the input signal from the push switches have some noise that can make the digit jump several places, this is due to button-bouncing and adding a capacitor across the switch will remove the problem.
The enclosure turned out real good, edges are aligned perfectly on the front and have some minor flaws on the back, but considering this is only made with a hand held saw and file I am satisfied.