06/20/2018 at 09:31 •
Nixie driving is quite straight forward. Connect the anode to high DC voltage (170-250V according to corresponding datasheet), and ground the cathode of the digit you want to illuminate, leave the other cathodes floating.
There are a few drivers available, and other projects may use different chips and methods, but I like the HV5530 Shift Register. It handles up to 300V, is 32bits (ie. it can drive 32 cathodes independently), has a Latch (ie. is not constantly cycling through each output, but keeps a steady array of output once latched) and interfaces easily with Arduinos via SPI.
Ideally interfacing is made through 12V (cf. datasheet recommended operating conditions), but from experience it understands 5V inputs without problems. The ESP32 being 3.3V only, may have some communication problem and I may have to use a voltage translator in order to step up my data from the controller to the driver, from 3.3V to 12V.
The HV5530 doesn’t come in a DIP package and is therefore not breadboard friendly for development and prototyping. In order to perform some tests and make sure it suits the clock needs, I made a breakout board on Eagle and had it manufactured in China.
As you can see below, I made an error in the package dimensions, and had to bend the legs of the chip in order to solder it to the board. You can admire my poor SMD soldering skills here as well (first SMD soldering experience).
It’s ugly but it works...
The Breakout board schematic and (corrected) board design with the HV5530 Eagle library are available on this project's files.
Soon we'll have a look at the driver in action and some corresponding coding examples.
06/13/2018 at 13:01 •
I’m planning to use 4 Nixies for this clock build. A 6 tubes build, besides showing the seconds, only offers the advantage of displaying the complete date in one go (DD-MM-YY or MM-DD-YY).
The latter can be accomplished if we split the date display in two (DD-MM then YYYY).
So how, many digits do I need to drive ?
Well, if we want to have all the digits available to us, this means 4 tubes times 10 digits equals 40 independent digits. Now for a specific clock build, the actual need is lower :
If we name each Nixie tube of the clock N1, N2, N3 and N4, then :
For a HH:MM time format, HH will be maximum 23, and MM 59, so for each Nixie :
- N1 can only be 0, 1, or 2 (total of 3 digits, for 24hrs display)
- N2 can be any digits from 0 to 9 (10 digits)
- N3 can only be digits from 0 to 5 ( 6 digits)
- N4 can be any digits from 0 to 9 (10 digits)
That lowers our need to 29 digits to be driven for the time display only.
For a DD-MM date format display DD will be maximum 31 and MM 12 :
- N1 needs to be able to display digit 3 as well as digits 0, 1, 2 mentioned above.
A MM-DD date format is already covered by previous digits selection.
So far we have :
- N1 = [0 - 3]
- N2 = [0 - 9]
- N3 = [0 - 5]
- N4 = [0 - 9]
For a total of 30 independent digits.
This allows to also cover a YYYY year display, with the following limitation :
We can display all years until 2059 then N3 is limiting the decades value to show. Ideally if we want to display year xx99, then N3 should contains all digits from 0 to 9 but this would bring our total digits required to 34.
Unfortunately the driver I’m planning to use only drives a maximum of 32 outputs (32 bits), therefore if we have N3 connected to digits 6 and 7 then we have a total of 32 digits driven and covers the years display up to 2079.
This is good enough for me, and I’d be quite happy if the clock lasts until then. After this date, in theory all would still function except the year display, which would only be available again in year 2100+. After all is this really important ?
One drawback of this is that some cathodes will never be lit as they are not connected. Those cathodes will be subject to cathode poisoning and may deteriorate over time.
To prevent this, if all cathodes were connected, one can code a cathode preservation routine, which would switch on all digits one after another in order to keep the wear of the whole tube equal and prevent unused cathodes to become contaminated.
In my case, the only way to prevent cathode poisoning would be to manually swap the tubes 2 by 2 every now and then (not sure about the frequency, but every year should do I guess). Tubes should therefore be connected to the PCB through pin sockets in order to be easily removed.
06/08/2018 at 16:25 •
A Nixie tube is in my opinion, a piece of art itself. The way it's manufactured and the way it looks even extinguished is a legacy of what technology was like in the 70's and underlines decades of technological improvements that brought us to where we stand today.
And the glowing. This orange captivating glow. Something I knew I had to have/make once I got introduced with Nixies.
Surprisingly, Nixies were not really made to look good, but to be functional. The most common Nixies we find nowadays are the soviet IN-12 ones. They are solid, cheap, and easy to source, but they have one flaw. The '5'.
The Russians got cheap and decided it was easier to use an upside-down '2' cathode to make a '5'. Though functional, this would have been better if they had designed the 2 with more vertical symmetry in the first place.
For a clock that will throw glowing number at my face all day, I wanted a more harmonious font. And upon searching a bit, I found on eBay some old French F9057 at a reasonable price. The datasheet is available online (in french) and you can find it in this project's files.
I bought those about 8 months ago, and left them in a drawer until I recently decided to have a go at this project. I bought a Nixie power supply able to deliver 180V DC from a 12V adapter, looked for a breadboard and plugged it in. Here is what the tubes and digits look like.
What do you think ?
Now that we have the face of the clock, we'll talk a bit about it's heart and how I'm planning to make it tick. Stay tuned.