[TUT] [HARD] [SOFT] How to build a Nixie Clock

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OK, my supply voltage is 177v (I might not quite understand what you mean by the supply votage vs the anode voltage though. this is the voltage before it hits the anode resistor.) my anode resistor is 3K ohms. with every thing wired up, I found an simple way to make sockets for IN-8s will post about that later, all the digits are lit. Any one care to tell me what I am doing wrong. And thanks for all the help so far, I hope to have a nice clock when I am done. :)

EDIT:
OK, never mind my problem. I apparently managed to forget witch side of my board was the negative bus, and was connecting the data lines from the chip all positive. what i meant to do was connect them low so "0" would light. please excuse me while I go stand in the corner for a while.

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Quote:
please excuse me while I go stand in the corner for a while.
15 minutes ..... AT LEAST :!:

A GIF is worth a thousend words   They are called Rosa, Sylvia and Tessa, You can find them https://www.linuxmint.com/

Dragon broken ? http://aplomb.nl/TechStuff/Dragon/Dragon.html for how-to-fix tips

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Hey I have the IN-8-2 and was wondering what resisters and voltage I should use. Thanks for the wonderful tutorial!

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Just checked: I use 180V and 33k anode resistor. Even with 50-50 multiplexing it's quite bright :)

Nard

A GIF is worth a thousend words   They are called Rosa, Sylvia and Tessa, You can find them https://www.linuxmint.com/

Dragon broken ? http://aplomb.nl/TechStuff/Dragon/Dragon.html for how-to-fix tips

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As Nard says, 180V and 33k is a good place to start. I've used that with IN-16 tubes. The IN-8 has slightly more cathode area but not enough to make much difference. If they're not bright enough you could try 27k but I doubt it will be necessary.

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I can suggest an alternative driver that would eliminate a few parts - the Supertex HV5522 (data sheet attached). This is similar in most respects to the HV5812 but has 32 open collector outputs that can withstand over 200V. So using this chip you wouldn't need the NPN transistors, just 100k resistors to the PNP bases, nor would you need the voltage divider. It has enough outputs to run a 4-digit clock unmultiplexed.

There's a catch. The data sheet says it needs a 12V logic supply. I have it on good authority (though I haven't tried it myself) that it runs reliably at 5V, but no guarantees. Since the outputs are specified to sink 100mA I expect the output FETs need 12V to turn on hard, but for the piddly 2mA in a Nixie application 5V turns them on hard enough.

I would have mentioned them before, but last year they were practically unobtainable except direct from the manufacturer. Now Mouser has them - twenty in stock when I got that URL.

Attachment(s): 

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So I have peret's 180V power supply working, and have tested my nixies. Now I'm working on driving them with the HV5812. I was wondering if anyone could give me a HV5812 101 course. The datasheet is very vague (like most datasheets). Tell me if I'm wrong, but you send it two bytes via SPI and then strobe it which tells it to latch the data. And each bit corresponds with a certain Q output. The last bit sent corresponding to Q1. The first bit sent corresponding with Q16, and the fact that Q17-20 don't have anything doesn't matter.

Thanks

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Quote:
...send it two bytes via SPI and then strobe it which tells it to latch the data. And each bit corresponds with a certain Q output. The last bit sent corresponding to Q1. The first bit sent corresponding with Q16, and the fact that Q17-20 don't have anything doesn't matter.

You've got it!

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I've got a Nixie clock! I programmed a ATmega16 using AVRGCC. I'm not sure if I want to add the alarm clock functions yet. I just don't know if I can trust myself pressing the snooze button gracefully enough every morning as the nixie tubes are quite fragile. I also have not taken the time to implement sleep in between second interupts. Oh and when I connected my tubes to the HV5812 I made a small mistake in the wiring, and instead of rewiring I decided to try an unconventional software fix. If anyone is interested, I can post my code.

Thanks to Everyone!

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agoessling wrote:
I've got a Nixie clock!

Congratulations!!!!!
Quote:
I just don't know if I can trust myself pressing the snooze button gracefully enough every morning

Heh, I put a mercury tilt switch out of an old thermostat in my alarm clock. With the feet well back from the edges, I can reach out blindly and push it in any direction to cancel the snooze - no need to fumble for a button. Another alternative is to use a large metal screw-top lid off a jam jar, solder a wire to the inside, clean the paint off the edge and mount it on top on a piece of foam. A ring of aluminum foil glued to the case makes the other contact, and bingo, a snooze button even a blind man couldn't miss.

Just one important point to remember, though - the snooze function needs to be a change of state, not a closure. It's too easy to leave the clock tilted, or something else on the table hold a big switch down, and then if simple closure cancels the alarm it won't go off.

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Oh another thing I forgot to mention, I ended up using 22K anode resisters with my IN-8-2. Driving direct (no multiplex) with 180 volts and 22K, each registered right around 2 milli amps. This was the lowest current that I could get my "3" 's to fire fully without flickering. Multiplexed these tubes at only 2 mA should last quite a while right?

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Hi there,
I wanted to rebuild your HV supply for the nixies. But I just ended up with 3 blown coils :D

I double checked to circuit and it looked like yours on the schematic.
I'm using an IRF640N instead of you MOSFET, because I had some of them lying around.
Also the coil... I used a small one that looked like a resistor. Is it right?

I tried the circuit without any software. Only to test if I got everything right before starting with the PWM. The pin was pulled to low. So there shouldn't be any problem.
After 2-3 seconds it blew the coil.

Do you know what I did wrong? Any suggestion would help. I'm a bit frustrated now :(

edit:
Oh! I almost forgot that:
Thank you for this great tutorial! ;)

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Quote:
After 2-3 seconds it blew the coil.

Coil selection needs to bear this in mind: the magnetic core of the coil has to store and release the entire energy used by the HV supply. Without going into the maths, it needs to be a fairly substantial chunk of iron or ferrite to store the energy. Small resistor-sized inductors don't have enough magnetic material to hold the energy, and to get the same inductance on a small core needs many turns of fine wire, so the resistance is not trivial. Result, the core saturates early in the switching period, the current rises out of control, the windings heat up and poof! The peak inductor current can be more than 1A and the core absolutely must not saturate at that current. It should also have a low enough DC resistance that it doesn't heat up. A suitable resistor-style inductor would be about the size of a 5W wirewound resistor.

The specified coil uses an T68-26A iron permalloy toroid with 1 cubic centimeter of iron, to give some indication of how much core material is enough. You can also use coils like the DO3340-224 (picture), which is a bobbin type core 9mm in diameter. Note the wire thickness. The important specifications are the saturation current and the DC resistance - 1.6A and 0.44 ohms for the DO3340, which is just about right for this job. Hint - Coilcraft are happy to give samples.

IRF640 is fine, if you keep your fingers off the exposed tab. You'll only touch it once :twisted:

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Quote:
I tried the circuit without any software. Only to test if I got everything right before starting with the PWM. The pin was pulled to low. So there shouldn't be any problem. After 2-3 seconds it blew the coil.

I just read your post again - do you mean the coil blew out when the FET was supposed to be turned off? In that case it sounds like a wiring error, or a shorted FET, or a shorted HV capacitor. My remarks above still apply to the coil selection.

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I double checked the wiring... Perhaps there was still a mistake. I ordered some new coils with a ferrite core.
I'm from germany. So I wanted to order it here: http://www.reichelt.de/?;ACTION=...@w4c29c2eba29f4a2c179fa89526676185
But I see right now:
Resistance: 0,32 Ohms
Current: 700mA

That's only about the half of your suggested coil.
I will try to get some samples here in germany or find a reseller for such a coil.

I thought from the beginning that these small resitor-type-coils don't do its job properly in this circuit.

You wrote that you don't want to digg in the math. But... Do you have a website about this topic? Even with the math? I'm an information technology student, so I don't have a big problem with this mathemathics stuff ;) I always need to do the math. I could imagine better things but if I need it, I can do it :)

IRF640.... Good advice! Thank you ;) Does the FET get very warm? Do I need to bother with some kind cooling? If yes, I've got a slight problem with the exposed tab for the reason you mentioned. ;)

edit:
http://www.reichelt.de/?;ACTION=...@w4c29c2eba29f4a2c179fa89526676185
Got one ;)
This thing seems to have the specs I need.

Or even better:
http://www.reichelt.de/?;ACTION=...@w4c29c2eba29f4a2c179fa89526676185

2,2A
and
340mOhms

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I wrote some stuff about it on http://www.aplomb.nl/TechStuff/Switcher/Switcher.html. That was for Dean, who wanted to have a HV-supply for a complete field Nixies. But I think it explains in an understandable way how it works, and how to do the math.

Plons

A GIF is worth a thousend words   They are called Rosa, Sylvia and Tessa, You can find them https://www.linuxmint.com/

Dragon broken ? http://aplomb.nl/TechStuff/Dragon/Dragon.html for how-to-fix tips

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Andy, either of those power inductors would be fine. If I'd known you were in Germany I would have suggested Würth Elektronik (click Power Inductors, WE-PD/WE-PD4 - I hate Flash sites that won't link directly). There you will find the two parts you selected. If you're interested in reading up on inductors, Würth publishes a very good design and reference book, the "Trilogy of Inductors". Find it on the "Design Kits" link, very last item on the page.

No, the specified IRF640 FET doesn't get warm, though I tried some others that melted.

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Cool, thanks.
I'll try to get a book about these stuff in my university library as soon as I get there again.

I hope that I can manage it to get this stuff working. I'll report it here.

Quote:
If I'd known you were in Germany...

I'm sorry! My fault ;)
I updated my profile. It's been some time ago I registered here and never set up my profile.

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OK.
I got all my necessary parts today. I wired it all up to a breadboard without a microcontroller. The gate of the MOSFET is pulled to low by R3.
Currently this is only for testing.

If I switch on the power, I measured on the high voltage output that there is a voltage of about 12V. If I switch it off, the voltage drops gradually from 12V to 0V.
This means that the current flows through L1 then D1 and there I can measure the 12V. After switching the power off, C3 gets discharged and the voltage falls gradually to 0V. Right?

Now If I would switch the MOSFET on and off, C2 is charged more and more by the inducted power of the coil and I'm happy with my high voltage output?

This should be right, shouldn't it?
I'm only asking because I don't want to blow it all up again. It smells horrible ;)

Last Edited: Thu. Sep 18, 2008 - 06:32 PM
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Yes that's right, that's exactly what you would expect.

The charging process is very fast - it only takes a few FET pulses to rise to 180V. You might want to put a load on the HV, say about 100k, to give the regulator some work to do and help stop it overshooting. R1/R2 helps some, but best to run it at the normal load. The FET duty cycle (scope it at the gate) will jitter a lot but should be between 10-30% depending on load.

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Cool. Now the software part ;)

I got some neon bulbs which are happy with 90V.
But I don't know how much current they consume.

How can I calculate the resitor for them? Testing? I've got some 100k resistors. Should I try them with the neon bulbs?

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100k is a good start. Make your choice based on the brightness in comparison with the tubes.

A GIF is worth a thousend words   They are called Rosa, Sylvia and Tessa, You can find them https://www.linuxmint.com/

Dragon broken ? http://aplomb.nl/TechStuff/Dragon/Dragon.html for how-to-fix tips

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Yeha... Works:
http://twitpic.com/c8lc

The 190V are slightly too high. It set it to 170V like the datasheet says. Anode resistor is 33kOhm.
But If I switch on the 1 I have a small blue ball of plasma (?) beside the glowing one. Is this right or is the voltage still too high?
If I set it to a lower value some of the figures do not light up fully.

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Quote:
But If I switch on the 1 I have a small blue ball of plasma (?) beside the glowing one. Is this right or is the voltage still too high?

It's a mercury discharge - the tubes contain mercury as well as neon. Don't worry about it, it will probably become less noticeable as the tubes burn in, but there will always be a faint blue mercury haze as well as the orange glow. You can hide it with a red or orange filter.

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No! I defintely like the bit of blue glowing around the orange figures!

I only noticed this rather big blue ball beside the 1.
So this blue glowing means my nixies are brand new? I bought 6 of them (IN-8-2) via ebay from a russian guy for only 18$ :) Really cool!

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I've got a new little question about the nixies ;)

I built the power supply with a nixie attached where only one figure was lit at a time. Now I took one of my 74141 and attached it to the µC. It's working but I saw some flickering in the several digits of the nixie. The 2 wasn't fully lit either.
Now I raised the voltage of the power supply to 217V. BEFORE the anode resistor of the nixie. The resistor has 33kOhms and the Voltage after it measures 137V to 152V depending on the lit figure.
Can I leave it with that? In the datasheet of my IN-8-2 stands that it has a firing voltage (is this the voltage where the figures start to start glowing?) of 170V and a keep up voltage of 100V.

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217V is over the breakdown voltage of the IRF640. Turn it down again at once - 170 is fine. You need 10% margin on the FET voltage, otherwise what will happen is the FET will break down drain to gate and damage its oxide layer, so although it will kinda sorta work, its breakdown voltage is compromised to about 100V or less. The spikes from the gate going back into the AVR will screw up the ADC circuitry internally so although it will kinda sorta work, sometimes the PWM clock will just stop for no reason and the HV drop to 12V until reset, or more confusingly, refuse to rise above 60V or so. You don't want to know how many hours I wasted chasing those twin faults in my prototypes.

Reduce the anode resistor if the glow doesn't cover the digit. Try 22k and then 15k.

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OK. I took 15kOhm. Now it seems to work with one nixie. Time to put it on a board :)

With 22k it also flickers and the two doesn't glow all over the digit.

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