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 Posted: Jan 27, 2008 - 01:13 AM |
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Joined: Nov 01, 2005
Posts: 6324
Location: Hilversum - the Netherlands
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Posted: Jan 27, 2008 - 09:30 AM |
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Joined: Dec 15, 2003
Posts: 4402
Location: Slovakia, Bratislava
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http://www.electricstuff.co.uk/oldbooks.html
Everything you wanted to know about discharge tubes, and were not afraid to ask, but never got an answer. |
_________________
There are pointy haired bald people.
Time flies when you have a bad prescaler selected.
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Posted: Jan 28, 2008 - 03:52 AM |
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Joined: Apr 19, 2006
Posts: 19
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| I am now one step away from my clock, But i hit a snag with my 74141 chips. If I pull all the data pins low witch should make the 0 pin active. It still lets the other cathodes light. Maybe I am missing something. For testing I have all the data pins wired to ground, and the +5 voltage applied. But if I take attach the cathode wire from one of the digits of the Nixie to the outputs. All of the outputs cause the Nixie to light, how ever all the wrong output pins are dimmer (then the one that is selected.) Any one have any ideas what I am doing wrong? |
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Posted: Jan 29, 2008 - 05:35 PM |
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Joined: Nov 01, 2005
Posts: 6324
Location: Hilversum - the Netherlands
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| What is the anode-supply-voltage ? If more than 185 ... 190V, then it's too much for the 74141 |
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Posted: Jan 30, 2008 - 05:19 PM |
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Joined: May 26, 2004
Posts: 2538
Location: Las Vegas, Nevada
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Quote:
But if I take attach the cathode wire from one of the digits of the Nixie to the outputs. All of the outputs cause the Nixie to light
The answer lies in these words above. The 74141 can only hold off about 80V. With only one cathode connected, the voltage across the tube will be enough to break down the 74141 and light it up even on the "off" outputs. If ALL the cathodes were connected though, the one which is selected would strike first and pull down the voltage (by the anode resistor) enough that there isn't enough voltage on the other cathodes to break down the 74141. Note, though, that you will never be able to blank a whole digit. |
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Posted: Jan 30, 2008 - 05:29 PM |
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Joined: May 26, 2004
Posts: 2538
Location: Las Vegas, Nevada
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Don wrote:
I'd be very interested if someone has come up with a good scheme for mounting IN-8 nixie tubes on a PCB.
Unfortunately, the Mil-Max sockets to fit those pins are too wide externally - a ring of them touch each other. I presume there's some kind of molded tube socket, but they probably cost more than the tubes.
On the subject of sockets, there's a widely available Russian socket for the IN12 oval end-view tube which looks as if it should fit the American B5991/NL8422 tubes. It does not. The pin circle is microscopically too large. You can work the B5991 in with a bit of effort, but after a brief pause (long enough to lull you into a false sense of security) the base of the tube cracks under the strain. I have a whole row of casualties to prove it. |
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Posted: Feb 01, 2008 - 04:20 AM |
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Joined: Apr 19, 2006
Posts: 19
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Plons wrote:
What is the anode-supply-voltage ? If more than 185 ... 190V, then it's too much for the 74141
Un-fortionally I don't have the power supply in front of me. If I remember correctly its ~~175V.
peret wrote:
Quote:
But if I take attach the cathode wire from one of the digits of the Nixie to the outputs. All of the outputs cause the Nixie to light
The answer lies in these words above. The 74141 can only hold off about 80V. With only one cathode connected, the voltage across the tube will be enough to break down the 74141 and light it up even on the "off" outputs. If ALL the cathodes were connected though, the one which is selected would strike first and pull down the voltage (by the anode resistor) enough that there isn't enough voltage on the other cathodes to break down the 74141. Note, though, that you will never be able to blank a whole digit.
So, the 74141s only work if I actually connect all of the cathodes? not just the one. |
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Posted: Feb 01, 2008 - 12:36 PM |
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Joined: Nov 01, 2005
Posts: 6324
Location: Hilversum - the Netherlands
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mmmlinux, I think you really need to measure the high voltage. Guessing will not bring you closer to good results.
If it's 175V (not on the anode of the nixie, but as supplyvoltage for the nixie), then you should be fine. I found that my 74141's started to turn all segments on @ 190~~195V.
Quote:
So, the 74141s only work if I actually connect all of the cathodes? not just the one.
I never tried that ....
What resistor-value do you use for the anode ?
Nard |
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Posted: Feb 01, 2008 - 05:37 PM |
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Joined: May 26, 2004
Posts: 2538
Location: Las Vegas, Nevada
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I believe it will be ok if you connect all the cathodes - let me put that another way - I believe the "off" cathodes will not light as long as at least one cathode is near ground potential. I don't know the exact physics of a nixie but I know that as long as there's an anode resistor and at least one cathode is struck, the anode voltage will be pulled down to the sustaining voltage, so the total supply voltage is immaterial.
One thing I do know about nixie physics is that almost all the voltage is dropped across a microscopically thin dark layer at the cathode surface, under the glow. If you could somehow probe the glow and measure its potential, it would be close to the anode voltage, not to ground. Electrons are accelerated up the steep potential gradient of the dark space and the glow happens when they collide with neutral neon atoms at the top. |
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Posted: Feb 09, 2008 - 12:22 PM |
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Joined: Jan 23, 2008
Posts: 1
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Peret,
Congratulations on an excellent thread!
The HV5812 appears just the ticket for my nixie clock for which I'm aiming at lowest part count so the serial interface is the way to go.
However, the part count on the anode drive circuit is bugging me so I'm looking for an alternative:-
I was considering using a bleed resistor connected from the anode resistor via a transitor to ground. Turning on this transistor would pull the anode voltage down below striking/ voltage and thus blank the display.
So the component count is reduced but at the expense of increased current (blanked tubes would would still draw current thorugh the bleed resistor)
Any thoughts on why this might not work?
Jonathan |
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Posted: Feb 09, 2008 - 08:48 PM |
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Joined: May 26, 2004
Posts: 2538
Location: Las Vegas, Nevada
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Quote:
Any thoughts on why this might not work?
Well, let's run some numbers. If the anode resistors are 33k and the voltage is 170V ... and let's suppose you don't pull the anodes to ground, but to half supply with another 33k resistor (see drawing) ... Then to blank a tube you will be pulling 2.6mA out of the high voltage supply, To blank five tubes takes 13mA. That is a dissipation of 2.2W, which would require a much bigger voltage converter and make the whole thing run uncomfortably hot. And 33k resistors will only do for the smallest tubes - if you use larger tubes they'll need smaller resistors for more current, which increases the losses proportionally.
So yes, it would work; but is it a good way to do it? I don't think so. You're trading six cheap transistors for a lot more cost and complication in the voltage step-up circuit - which, I should point out, is already the most stressed part of the system, and the usual failure point - and more heat than you really want to deal with in a closed box that runs 24/7. Those six PNPs buy you a lot of reliability. |
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Posted: Feb 09, 2008 - 09:57 PM |
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Joined: Apr 19, 2006
Posts: 19
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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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Posted: Feb 09, 2008 - 10:20 PM |
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Joined: Nov 01, 2005
Posts: 6324
Location: Hilversum - the Netherlands
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Quote:
please excuse me while I go stand in the corner for a while.
15 minutes ..... AT LEAST  |
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Dragon broken ? Or problems with the Parallel Port Programmer ? Scroll down on my projects-page http://www.aplomb.nl/TechStuff/TechStuff.html for tips
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Posted: Jul 27, 2008 - 11:31 PM |
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Joined: Apr 25, 2008
Posts: 48
Location: Dexter MO
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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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Posted: Jul 28, 2008 - 02:13 AM |
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Joined: Nov 01, 2005
Posts: 6324
Location: Hilversum - the Netherlands
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Just checked: I use 180V and 33k anode resistor. Even with 50-50 multiplexing it's quite bright
Nard |
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Posted: Jul 28, 2008 - 06:23 PM |
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Joined: May 26, 2004
Posts: 2538
Location: Las Vegas, Nevada
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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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Posted: Jul 28, 2008 - 07:12 PM |
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Joined: May 26, 2004
Posts: 2538
Location: Las Vegas, Nevada
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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. |
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Posted: Aug 03, 2008 - 11:31 PM |
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Joined: May 15, 2005
Posts: 78
Location: Dexter, MO USA
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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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Posted: Aug 04, 2008 - 06:17 PM |
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Joined: May 26, 2004
Posts: 2538
Location: Las Vegas, Nevada
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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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Posted: Aug 06, 2008 - 06:53 AM |
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Joined: Apr 25, 2008
Posts: 48
Location: Dexter MO
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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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