Archive for Nixie Tube Clock

Nixie Clock circuit finally complete!

Nixie clock circuitry finally complete!

It may have looked like I fell off the earth, got distracted by shiny things again and dropped my electronics projects – again. Well… NOPE. I’ve been furiously, wildly and tediously soldering this beast together.

Things I learned along the way

Well, the first thing I learned is that building anything beyond a simple project is a right pain in the arse on these solderable prototyping boards. I do like their convenience, and previously I had assumed I would be limited to using this and other perfboard-type prototyping boards, but from here on out, I’ll be making proper PCBs. You’ll see why below.

A right rat’s maze

One big drawback to making your projects on perfboard or solderable breadboard or similar is the sheer number of solder joints you have to make. Not only do you have to seat all of your components and solder them in, but you need jumpers or longer wires to anywhere it has to connect to. This is fine for a simple design, but in this case, it got obscene on board two.

This is why one should get PCBs made. This took forever.

This is why one should get PCBs made. This took forever.

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Clockin’ it

Been really trying to move along with this project, keep that wave of enthusiasm going and all that. I’m happy so say I have the first board complete!

Quite a rat's maze, I know

Quite a rat’s maze, I know

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Neon lamps, flashy LEDs, and soldering along the Nixie trail

Over the last couple days, I really sat down and sorted a couple of things that were unknowns. Either I had forgotten why I designed it that way on the schematic or had only roughly figured it out in the first place. One was the flashing LEDs from the last post. I had subsequently tried other resistor values for different effects, but in the end stuck with the 1.5kΩ one. I did like the blanking and hopefully it will be a nice effect once i have it all assembled. I can always change the resistor later if I wish.

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Steady on the Nixie trail

I’m trying to keep going and have some bench time every day to keep things going. So far, so good.

I figured the next bit to sort was how to move the decorative flashy LED feature over to the 12V rail. As mentioned before, I want to keep the 5V side exclusively for the clock and digital logic so it keeps its time when I unplug it (provided I have a 9V battery in it of course).

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Nixie tube clock gets a revisit… after a few years

It’s been a long time since I’ve written anything about… anything. As always, I’m happy if anyone finds the information here useful, but I don’t expect anyone to read it really or give a toss. Really use it as my open lab notes which I refer back to when I take these long breaks to remind myself just what in the hell I was doing!

I have a fairly good memory. To the surprise of some I can recall conversations verbatim from twenty years ago… but I know the instant I say “oh I won’t bother noting that, I’ll remember for sure…” is the moment that said information is forever wiped from existence, never to be seen again. One such, happened when I revisited my Nixie Clock project which I’ve been working on since… 2012 probably?

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Return, re-education, progress

So, after a long hiatus I am back in the lab and back to try and finish at least one damn project before I die. Started innocently enough, was bored on an evening and not knowing what to do with myself I thought I’d catch up on some of Dave Jone’s excellent video blog entries. Naturally, his energy and charisma stoked the flames of interest and had me missing the heady smell of flux and the hum of an energized transformer. I looked over what I had on the go and found with delight that I actually remembered a lot and was able to get back to where I was intuitively in no time at all (read: a couple of weeks of review).


Here I’ll summarize the projects I have on the go before I get to the good stuff – the experiments.

Nixie Clock

Almost finished. Kinda. Sorta. The schematic I reviewed for any errors and made sure I got everything right – no problem. I gave the half-finished board a good look-over and found it just fine, needing only to be populated. I know for certain I will be needing a second board on top of it, which is fine, to house the ridiculous number of high voltage transistors as well as the remainder of the 4017 counter ICs. I mapped out a plan of how i’m going to do my interconnects as well and puzzled over the problem of having something like 30 connections going from one board to the other. This is what happens when you use data that isn’t multiplexed and no microcontroller, you basically end up with a lot of wiring. For the power connectors and a few other things I don’t mind using molex style PCB connectors but I was faced with a challenge of how to route the 16 connector outputs from the bottom board 4017s to the top. I briefly flirted with the idea of keeping them all on the same board but then I would end up with 28 odd connections I would have to take to the second instead of 16. So with that in mind it dawned on me that the old IDC connector and the ribbon cable are ideal for this application! I’ll pick some up at the shops when I finally make it down there. As always, I’m s a few parts short on every project so it’s a worthwhile journey. All this one needs apart from this is a few switches to set the time some way to mount the nixie tubes securely and safely and of course a box to put it all in.

Power Supply

The power supply is, and always was, a beast of a project. Some do their first power supply simply but I wanted something flexible, cool, powerful, and more or less something I will want to use years down the road. The inevitable revisions take forever and the whole project is quite complex by this point. As I’ve mentioned before I’ve broken it into modules to make it easier on myself: AC Power, Pre-regulator, Current Limiter, Voltage Regulator, Control and display.

The AC Power board, as shown from previous posts, is complete and overall I’m quite pleased with it. It does have a rather high DC voltage output of ±42.6V which necessitates the inclusion of the pre-regulator block (mentioned previously) but otherwise performs just fine and will take more than I could possibly throw at it before it dies. Subsequent video watching and research has made me want to add the rather important addition of MOVs (Metal-Oxide Varistors) to add some over-voltage protection to the AC input of the supply though this is a rather trivial addition and simply have to add one each between the hot-ground, neutral-ground, and hot-neutral. I will probably add them to the rectification board or may have them on a separate board or hanging off the terminal block, I have not yet decided. Over-current protection is already present in the 5A hot fuse in the terminal block, as well as redundant case fuses I will employ in the final build. There is also the question of the ground lift. Research has shown me the wisdom of not tying the centre tap of the transformer (the 0V rail) to mains earth so with that in mind I will keep it floating by default with an aircraft switch on the front to enable mains earth referencing should I need it. Easy.

The pre-regulator has seen much progress since the last time I took a poke at it. I had previously included it, discarded it, then included it again in a much more workable form. After much fiddling in circuit lab, I settled on using a zener diode/darlington transistor regulator and crunched all the numbers into a workable solution. I did build it up and test it but will expound on my results in a subsequent blog post. The upshot is I can knock that crazy 42.6V down to much more usable 28-29V and have it work over a variety of loads which is nice. There still is the question of stability and whether or not it will play nice with the rest of the circuit.

The other modules are untouched from last check. It will be a long time before a completed product. I’m still fuzzy on a bunch of things and I’m expecting pitfalls along the way which could be both frustrating and highly amusing. Of course, that is why i’m doing this in the first place – I’m learning, and that is its own reward.

Dummy Load

Of course this ties in closely with the power supply project as I need some practical way to test the thing under working conditions not to mention calibrate it. It has taken a back seat to other projects yet I will have to build it to build my power supply. Projects always lead to more projects. It all started, as mentioned previously, with Dave Jone’s excellent example, but I’ve been further spurred on by the discovery of Martin Lorton’s excellent version which will probably be much more suited to my needs. Naturally, I will add my own modifications to both make it my own and to suit my needs. Martin’s has a 2A cap (I believe he reduced it to 1500mA by the end though) and I need mine to sink 3A to properly test my power supply. It should be a simple matter of selecting the right mosfet and/or using mosfets in parallel.

Given that this project is likely to take me as long as the others and I still have not been able to leave my house to grab the appropriate parts, I went back to why I need this damn thing in the first place. The easiest solution for a dummy load is to of course whack the right value resistor that can handle the power you want to dump through it. This has proven most frustrating since not only do I not have a collection of power resistors on hand, but finding ones with the appropriate tolerance and power dissipation capability has proven to be difficult.

I decided for a more low-tech approach and see if I could make my own power resistor to act as a static dummy load just for now. That is a subject of the next blog post which I will marry with the power supply pre-regulator test. Quick answer: I did, and it not only worked but I’m still alive and my house is still standing.

New Projects

Always something new an shinier on the horizon, isn’t there? This is why I never get anything done.

Milliohm meter

Keeping with the theme that projects beget other projects, the power supply needs a dummy load, the dummy load needs a precise high power low-ohm resistor, I need a way to measure low resistances. It’s commonly known that most DMMs do a woefully awful job of measuring low resistances. One has to dump enough power into it to see a measurable result, and things like the leads now have a nontrivial resistance. So I started building an adaptor for my multimeter that fixes these problems. A post will be written on this also. No, I didn’t finish this either.

eGo Charger

This is merely an idea and a helpful schematic posted by someone on a forum somewhere. One of my eGo chargers for my ecig is malfunctioning and not doing it’s job and I sit here rather nervously waiting for my one functioning one to die and deny me my fix. I’m merely thinking about this one for now, if I get it wrong i’ll have explody batteries on my hands so you can bet I’m going about this one carefully.


Made sure I did something constructive today…

Added on to my circuit board from the previous post. This is the heart of any clock: the crystal oscillator. I’ve explained it more or less in previous posts, a 4.194304MHz quartz crystal is set oscillating while a CD4521 24-stage frequency divider divides the frequency in to discrete steps by powers of 2. Of course the primary use for this is to get a clean 1Hz output from the thing.

After smacking my forehead and soldering one joint I forgot about when the initial test didn’t work. I’m happy to report it is working just fine. Here’s some pics and a video of the scope readout on my crappy (but working) PM-3200:


I think I had it set on 2 volts per division and there’s some parallax error from my crappy camera skills but there you have it. You can see that half at least of the board is still unpopulated and this will house the two seconds counters which will take the output of the 1Hz (i.e. one pulse per second) and convert that into counting minutes. Unfortunately, I highly doubt I will be able to fit the minutes and hours counters on the board (though it might be fun trying, $10 says I burn myself) so they will live on a board which I will mount on top. Beyond this, it is going to be a very boring wiring maze.

I have yet to find a suitable box for it, time to raid antique and junk stores methinks… if only I could work with wood (and make it look good) I would build my own, but alas, I stink at carpentry.

Progress amid much laziness

Nixie supply soldering coming along!


Winter is hard, it’s cold, there’s not enough food, the hounds attack… wait. That’s my video game. Relevant though, because that’s exactly what has been distracting me from making serious progress on my electronics projects. I am referring of course to Don’t Starve. Sometimes though, I have to force myself to haul my ass down to the basement and get something done – or I never will. I have a long history of procrastination and it’s time I finish a few things with electronics before the ice thaws.

Today, I managed to get down there and solder some more. Like many things, it’s easier once you get into the rhythm of it. I’ve never been great at soldering (see my previous post on the voltmeter sub-project) but it’s exactly true that practice makes perfect. I’m finding with each successive try, I am making better, cleaner, shinier joints that are less likely to short or crack or be non-functional.


Today is a landmark. The first time I soldered something up and it worked. I didn’t have to reflow any joints or troubleshoot mistakes, it worked. I couldn’t be more pleased. From the pictures here you can see me assembling my nixie clock and what I have done so far is solder on a triple power supply. The first two are quite simple using LM78xx regulators to gave me +12V and +5V. No explanation needed there. The second feeds off the 12V and uses a switchmode circuit to bump it up to 170V – the butter zone above strike voltage for my nixie tubes.

After a couple hours of soldering and a quick trimpot calibration, it reads 170.2V. Brilliant.

Next step is to fit the oscillator into the small space beside it to the left which consists of a 4521 frequency divider, a crystal and some passives.

Nixie Clock Schematic Finished

After a lot of testing, it’s looking good!

My Nixie Clock Schematic

My Nixie Clock Schematic

So here is my more-or-less final schematic. Since I used bits ripped off from a bunch of places and cobbled them together, use it freely for your own clock project. Schematic posted here.

Please of course bear in mind that though I’ve made an effort not to make mistakes on the schematic, they are bound to be there so if you build this and hurt yourself because you didn’t check your work, well that’s your fault isn’t it? You’ve been warned. Some parts of this circuit have potential around 170Vdc which will zap you good!. I very much doubt the the circuit can kill, but I don’t want to see a test of that either. Enough, you get the point.

So I am quite pleased. Although I’ve been unable to breadboard up the entire thing at once, I’ve built it in pieces and it seems to work well. Quite low power also, I reckon the thing draws 150mA or less. I will have to wait a bit to give a measured reading on that as I accidentally melted one of the fuses in my multimeter and will seek a replacement for it.

Things put in, things left behind

There are many things I added to this circuit to give it some functionality and to make it usable. One can set the hours and minutes independently using push-button switches and in this sense works just like an alarm clock. There is also a seconds reset button which will zero out the seconds when whatever your setting it to reaches zero seconds to keep them close to in-sync. Holding down the button also acts as a seconds-hold so that’s quite useful. These three should be push-button momentaries, the type that have three terminals: a normally closed, input and normally open. The seconds reset needs to be double-pole double-throw momentary. All cheap and easy to find.

I’ve helpfully labelled the transistor pinouts as well. As it happens, I seem to have selected ones with every type of pinout combination possible. Infuriating really, why can’t they just stick to one standard one? Doesn’t matter what it is, just make it the same! All of the parts here, apart from the nixie tubes themselves, are cheap as chips and commonly available.

How it works

The circuit is divided into five basic sections. At the bottom left we have the 5V power supply (simple 7805 regulator) which powers all the CMOS chips as well as the crystal oscillator and the vanity LEDs. Moving right we have the 4521 frequency divider IC and the crystal oscillator. The resistors and caps start the crystal resonating and the 4521 divides its frequency down to the desired pulses we need for other parts of the circuit.

At the bottom right is the blue ultra-bright vanity LEDs which I plan to mound under the nixies to give them a nice nuclear blue glow that I’ve seen from other projects. Gotta have that! It pulsates once every four seconds and uses an RC timing circuit to fade it in and out. It should be noted that this circuit causes slight voltage fluctuations elsewhere in the circuit though these seem to not effect it’s function at all.

Above that we have our 12V Supply. I chose a 12V wall wort, since they are frequently over voltage anyway and as it happens it overcomes the 7812s dropout voltage to make a reasonable 11.90V. Moving right we have the small switch-mode supply that steps up the voltage for the nixies to about 170Vdc. This is quite a lovely circuit I lifted in its entirety from stuff posted around the net (see my previous posts for schematic). It is quite reliable and works well. As I mentioned in previous posts, it has a maximum output of 10mA. Since each nixie draws about 1.25mA, and each of the neons that make the separator colon draw about 1mA, we are only up to 7mA. Plenty of headroom. This saved me from having to step up un-isolated mains voltage and makes the whole circuit a damn lot safer.

The third row up from the bottom is where all the time calculation happens. Six 4017 counter ICs are used, one for each digit. Since the clock only has four nixies, the first two (the 1s seconds and the 10s seconds) are left with their outputs unconnected. Function couldn’t be easier: the 1s seconds accepts the 1Hz signal from the 4521, counts to ten then resets, passing a signal to the 10s seconds 4017 IC which counts to six and resets, passing it on to the minutes and so on. The function of the three switches is explained above and the hours in the previous post.

Finally, at the top we have the four nixie tubes and two neon lamps for our display. Each number of each digit (and the pair of neons) are driven by the MPSA42 high voltage transistor which accepts the input from the appropriate counter IC output via a 33k resistor. This works wonderfully. The two neons use the same transistor, but use the 1Hz signal from the 4521 as an input.

That’s it really. Better explanations of how this works are out there written by others more eloquent than I.

If you are going to build this up, I would highly encourage you to examine the circuit closely and test as you build it up. For a beginner project (as that is what I am still) this has some quite excellent educational value.

So now, I just have to build it up. The last challenge is, of course, to select (or build) a suitably attractive case for it. I’m hoping to hunt through a few junk shops for a nice box I can use.

Nixies on display

and the tiny amount of current that drives them

Here’s just a quickie post to show off my Hivac XN11 nixie tubes. I simply brought out the power supply for them and hooked up all four to various numbers. Nothing special apart from the nixies themselves which I find nerdtastially beautiful! Here:


Isn’t that a thing of beauty? I hooked all four of them up (for the first time ever as it happens) to try and get a current reading to see if I might be in danger of overloading my power supply. This is a serious consideration considering such high voltages (~170Vdc) bad things could happen if I get to close to the edge. I was delighted to find that four nixie tubes draw a measly 4.67mA. Considering my power supply for them is rated for 10mA, I’m in business!