Arduino Forum

Using Arduino => Displays => Topic started by: cowjam on Jan 27, 2011, 10:42 am

Title: Nixies: stupid questions.
Post by: cowjam on Jan 27, 2011, 10:42 am
Firstly, I wasn't sure whether a nixie thread should go under displays or LEDs/multiplexing, so I plumped for here. I reckon I can get away with it, I've been here a while but right now I'm feeling like a complete n00b and that I haven't learnt anything in the eight or so months I've been messing around with arduinos. Anyway...

I have a nixie tube socket wired up to a breadboard (with a nixie in it).
I have suitable 180v, 12v and 5v supplies.
I have a 74141 (although it's russian so it's labelled differently. I have checked and the pin out is identical).

I have tested the nixie by running individual pins (not using the 74141) and it works fine.

I then wired up the chip as per the usual pinout (example (http://premiumorange.com/daniel.robert9/Digit/images/74141.GIF)), using 5v for the Vcc and popping the four logic pins into the arduino.  I then knocked up a basic sketch which switched the pins low/high according to the number, aiming to go from 0 to 10 in sequence.

This is where I hit a problem.  Numbers stayed illuminated. 
I'm afraid I wasn't paying enough attention to spot whether some or all of the previously illuminated numbers stayed lit up (they weren't going in the correct order but that shouldn't matter).
I removed the arduino and some numbers stayed illuminated (powering off before doing anything).
I set all the data pins to ground, no change.
I removed the Vcc, no change.
I tied the Vcc to ground, no change.
I removed the data pins and Vcc, no change.
I removed the ground pin - no output. Put it back, no change. The same digits were lit up.

Have I broken the 74141?  Is there something I need to do to clear the chip when changing numbers?
Title: Re: Nixies: stupid questions.
Post by: cowjam on Jan 27, 2011, 01:07 pm
The nixie is running on 180v.
The 12v powers the arduino and nixie PSU.
The 5v is for chip logic (vcc input).

I have the nixie hooked up to the 180v + and the ten other nixie leads linked to the chip.

The chip has four logic pins coming from the arduin (5v), one 5v Vcc, ten nixie -ve connections and one ground connection.

I'd a tad confused - why would a nixie control chip not run at nixie voltages?  Everything I read beforehand said I needed 120 - 180v to power a nixie.
Title: Re: Nixies: stupid questions.
Post by: MarkT on Jan 27, 2011, 05:30 pm
Nixies are gas discharge devices - when not conducting they are basically open circuit, and to conduct a minimum strike voltage is required across the electrodes.  When conducting they need at least a minimum voltage to keep the discharge going.

The upshot is that driver circuit never gets to see the full supply voltage, so it is possible to drive with parts rated less than the supply as the off-state leakage current of the driver is plenty to keeps the nixie cathodes at a low enough voltage.  The on-state voltage of the driver will be low if the drivers are low-impedance - again no problem.

The only problem is the switching transients as the nixies are conducting and the driver is not fully on - the difference of the supply and minimum nixie-on voltage will be present briefly across the driver - if this is too high the driver will be damaged.  So if the supply is 180V and the min on-voltage is 80V, the driver needs to handle 180-80 = 100V...

So if you have datasheets for both tubes and drivers you should be able to work out if its a safe combination - the supply voltage can be lower than the nominal nixie voltage so long as its above the strike voltage - the tubes will be dimmer.

Also I seem to recall that you are supposed to use load-resistors to drive nixies, and these can drop some of the voltage and help protect the drivers.
Title: Re: Nixies: stupid questions.
Post by: wyager on Jan 27, 2011, 08:50 pm
Are you using an anode resistor? That's crucial. It sounds to me like something's up with your driver IC. Can you post a schematic?
Title: Re: Nixies: stupid questions.
Post by: cowjam on Jan 28, 2011, 12:57 am

Are you using an anode resistor? That's crucial. It sounds to me like something's up with your driver IC. Can you post a schematic?


No, what size resistor?

My circuit is as described - no resistors or caps or anything.  The nixie plugs into the IC and 180v+, the arduino plugs into the four IC logic pins and the IC is also linked to +5v and GND.  All the grounds are linked.
Title: Re: Nixies: stupid questions.
Post by: wyager on Jan 28, 2011, 01:18 am
OK, that's a problem, but I'm not sure it's causing your problem. What nixies are you using? Most people reccomend between 15 and 33k resistors, but it really depends. What you want to do is find a resistor (and you will have to experiment between those two values) where when you measure the voltage across the resistor and divide it by its resistance to find the current passing through it, and it should the recommended (you could go a little under and be fine) current for the nixie tube (small tubes tend to be around 1.5mA, medium tubes 2.5mA, and large tubes 4+mA. A model number would help). You have to experiment because of the variable nature of the nixie tubes, no one is exactly alike. So if you use a 15k resistor and find that the voltage dropped over it is 30V, you know that you are passing 2mA through your nixie tube which should be fine.

Also, what are you using as a power supply? If your 180v power supply does not have a built-in output filter cap, you will want to install one. 1µF @ 250v is probably enough to adequately filter the voltage.

Also, one possibility is that your tube has a severe internal short or something (but this is very unlikely). I recommend (after installing the resistor) individually testing each digit (without a decoder IC) to make sure the tube works well.

Good luck with your nixie project, as I think you know I am doing the same thing.  ]:D
Title: Re: Nixies: stupid questions.
Post by: FEDERICO on Jan 28, 2011, 01:53 am


Are you using an anode resistor? That's crucial. It sounds to me like something's up with your driver IC. Can you post a schematic?


No, what size resistor?

My circuit is as described - no resistors or caps or anything.  The nixie plugs into the IC and 180v+, the arduino plugs into the four IC logic pins and the IC is also linked to +5v and GND.  All the grounds are linked.


For what I know this should work. I have a couple of nixies here and I am starting to work with nixies those days. I will give a try to this setup (that should work, in my opinion)
F
Title: Re: Nixies: stupid questions.
Post by: MarkT on Jan 28, 2011, 02:41 am


Are you using an anode resistor? That's crucial. It sounds to me like something's up with your driver IC. Can you post a schematic?


No, what size resistor?

My circuit is as described - no resistors or caps or anything.  The nixie plugs into the IC and 180v+, the arduino plugs into the four IC logic pins and the IC is also linked to +5v and GND.  All the grounds are linked.


The resistor depends on the specs of the Nixie in question.  For instance I have some sub-miniature Russian IN-17 nixie clones that are speced for 170V and 47k series resistor.  The sheet I have says they will work at lower voltages and upto 82k series resistor.  The series resistor goes on the anode to avoid having resistors for every cathode (which can directly connect to the driver).

That said I haven't tried interfacing these tubes yet, I've merely verified they light up.
Title: Re: Nixies: stupid questions.
Post by: cowjam on Jan 28, 2011, 11:07 am
Thanks.  They're number 12s.  I got a dozen of them, sockets and the ICs from Ukraine (gotta love ebay!) - they look Russian (cyrilic writing on them).

I'll have a play tonight and see what else I can break ;)
Title: Re: Nixies: stupid questions.
Post by: cowjam on Jan 28, 2011, 07:17 pm
I've got them working, thank you everyone (especially wyager).

I slapped a 33k ohm resistor on the anode and it's working fine now using a fresh IC (I've permanently damaged the first one). 
Title: Re: Nixies: stupid questions.
Post by: wyager on Jan 28, 2011, 08:42 pm
Excellent! It was probably just too much current that damaged the old IC.
Title: Re: Nixies: stupid questions.
Post by: cowjam on Jan 28, 2011, 08:59 pm
Yeah. I'll get the hang of this electrickery stuff eventually!
Title: Re: Nixies: stupid questions.
Post by: cowjam on Jan 28, 2011, 10:30 pm
Spoke too soon! http://arduino.cc/forum/index.php/topic,50274.msg358237.html
Title: Re: Nixies: stupid questions.
Post by: wyager on Jan 29, 2011, 05:26 am
No! That's awful!  =(
Title: Re: Nixies: stupid questions.
Post by: FEDERICO on Jan 29, 2011, 03:39 pm
I am following your experiment and as soon as I finish my pov experiment I will apply them to nixies...
Where did you find the datasheet for yours?
I have just tried to light up my IN-14 from my DCDC power supply but I am quite sure that the others little blulbs that I have, IN-3 (just neon bulbs) can't work at 170v...
Title: Re: Nixies: stupid questions.
Post by: cowjam on Jan 29, 2011, 03:59 pm
I googled for it.  Not sure I had a datasheet for my actual nixies, but I got the datasheet for the chips (which came with the nixies) by googling, and this is it: http://cowjam.co.uk/arct/k155id1.pdf

I've got some IN-35s which are just neon bulbs and they run fine at 180v (or whatever my circuit is running at) and ran fine with or without a 33k ohm resistor.
These ones: http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&item=390206146006&ssPageName=STRK:MEWNX:IT#ht_864wt_905
Title: Re: Nixies: stupid questions.
Post by: FEDERICO on Jan 29, 2011, 04:17 pm
We bought nixies from the same vendor :-)
Mine are those
http://cgi.ebay.it/ws/eBayISAPI.dll?ViewItem&item=400174245756&ssPageName=STRK:MEWNX:IT
I am going to try to drive them at 170v and see...
After reading about your experience I was thinking that multiplexing and optocouplers should be the safest way...
Title: Re: Nixies: stupid questions.
Post by: cowjam on Jan 29, 2011, 04:22 pm
Yeah, optocouplers are the way to go! 

If I figure out what happened I'll report back on here.
Title: Re: Nixies: stupid questions.
Post by: wyager on Jan 29, 2011, 08:31 pm
BTW guys, small neon bulbs should have at least 100K resistors (some use 200K) at 170+V or else they could burn out themselves or your circuit. I am able to multiplex them at 170v with a 100K resistor. Remember that the gas inside them will change its resistance until the voltage across the lamp is the sustaining voltage. A 200K resistor (which is probably better for long life) makes them look a little sputtery.

My A1As regulate themselves at 60V, which means that 110V gets dropped over the anode resistor. 110V/100000?=1.1mA. Almost twice the recommended amount, but I figure since I'm multiplexing... Still probably not healthy.
Title: Re: Nixies: stupid questions.
Post by: FEDERICO on Jan 29, 2011, 10:41 pm
wyager, thanks a lot for the advice. I am going to follow it!
Title: Re: Nixies: stupid questions.
Post by: cowjam on Jan 29, 2011, 10:48 pm

wyager, thanks a lot for the advice. I am going to follow it!


This ^ !
Title: Re: Nixies: stupid questions.
Post by: wyager on Jan 29, 2011, 10:52 pm
No problem. Also, 666 posts cowjam.  8)
Title: Re: Nixies: stupid questions.
Post by: FEDERICO on Jan 29, 2011, 11:17 pm
the number of the beast  ]:D

By the way i see that you (wyager) use a lot of transistors for driving your project. Don't you have a 74141 off hand?

ps. the optocouples i need, TLP627, are damn expensive  :smiley-eek-blue:
Title: Re: Nixies: stupid questions.
Post by: wyager on Jan 29, 2011, 11:35 pm

the number of the beast  ]:D

By the way i see that you (wyager) use a lot of transistors for driving your project. Don't you have a 74141 off hand?

ps. the optocouples i need, TLP627, are damn expensive  :smiley-eek-blue:


I was basing my project off parts I could get from digikey and I couldn't find any HV nixie drivers. The MPSA42s were only like 5 bucks for 25 IIRC, so I just went with those. I suppose after the shift registers and resistors and perfboard, the 74141s off ebay would have been cheaper, but it was a learning experience anyway.  :P

BTW, are the optocouples to protect the rest of the circuit from high voltage?
Title: Re: Nixies: stupid questions.
Post by: cowjam on Jan 30, 2011, 06:04 pm
I don't know if this will have contributed to the burnout, but I have discovered that I'd got the pins all muddled.

The power and ground pins were fine, but I had misinterpreted the position of the nixie pins so that I had the number sequence reversed.

I had also failed to spot the utterly confusing layout of the logic pins on the IC.  If you look you'll see that the pins are labelled A, D, B, C (in that order).  The logic chart is labelled D, C, B, A. 

I will have undoubtedly sent things to the IC that it wasn't expecting, though the logic chart says that should merely have resulted in no output.
Title: Re: Nixies: stupid questions.
Post by: FEDERICO on Jan 30, 2011, 06:29 pm

BTW, are the optocouples to protect the rest of the circuit from high voltage?


I need them for multiplexing the nixies. If I connect all the cathodes to the nixie driver IC then I need a way to switch on the 170v anodes. I am experimenting the tlc5940 but I can't let it manage the high voltage. That's way I tought about optocouplers connected to the high voltage anche my TLC to open and close the gate.


I had also failed to spot the utterly confusing layout of the logic pins on the IC.  If you look you'll see that the pins are labelled A, D, B, C (in that order).  The logic chart is labelled D, C, B, A. 

So the datasheed is wrong?? Anyway it looks like a strange way for burning an IC...
Title: Re: Nixies: stupid questions.
Post by: cowjam on Jan 30, 2011, 06:43 pm
No, the datasheet is fine. I hadn't read it properly.
Title: Re: Nixies: stupid questions.
Post by: cowjam on Jan 30, 2011, 06:55 pm
Another question: Ground sharing.

Do I share the ground for the 180v and 5v circuits?
Title: Re: Nixies: stupid questions.
Post by: FEDERICO on Jan 30, 2011, 07:02 pm
Just in time, I was going to ask the same question. I think that no, for what I can understand for driving for example the neon bulbs you have to ground them to the arduino with the high voltage mpsa42 transistor, right?
Title: Re: Nixies: stupid questions.
Post by: cowjam on Jan 30, 2011, 07:14 pm
I hope someone answers soon, I'm about to run another set up (using a shift register) and I don't to kill anything else.

Thing is, the 74141 has one ground pin and runs 5v and high volt so that must share a ground, right?
Title: Re: Nixies: stupid questions.
Post by: FEDERICO on Jan 30, 2011, 08:09 pm
In the 74141 there are transistors on each pin... I am waiting for hints too ^_^
Title: Re: Nixies: stupid questions.
Post by: cowjam on Jan 30, 2011, 08:14 pm
My shift register is running with shared ground.  

When I say "running" I mean the nixie lights up and changes and the arduino hasn't caught fire. It isn't doing what I expected in the slightest though.

Edit: Working properly now. I'd not paid enough attention again.  Missed one of the ground pins for the 595 and had hooked the 74141 up to shift register pins 1-4 instead of 0-3.

Time to add a second nixie.
Title: Re: Nixies: stupid questions.
Post by: wyager on Jan 30, 2011, 09:01 pm

Another question: Ground sharing.

Do I share the ground for the 180v and 5v circuits?


Yes. Ground must be shared between all circuits, just be sure never to share VCC. I suppose you could, theoretically, make separate circuits with optoisolators, but for what we are doing that makes no sense. I have had no problems sharing ground between all of my circuits, just keep the high voltage separate from low voltage through transistors, driver circuits, whatever.

Edit:oops, didn't see there was another page. Glad you figured it out. As you can see from my schematic (I think I posted that here) I'm just driving a bunch of MPSA42s from a shift register.
Title: Re: Nixies: stupid questions.
Post by: FEDERICO on Jan 30, 2011, 09:41 pm
Are the Mps42A switching the anode?
Title: Re: Nixies: stupid questions.
Post by: cowjam on Jan 30, 2011, 09:45 pm

Are the Mps42A switching the anode?


Why do you want to switch the anode?

If you're using 74141s sending an out-of-range command (ie, all four pins HIGH) then the nixie doesn't display anything.
Title: Re: Nixies: stupid questions.
Post by: cowjam on Jan 31, 2011, 12:21 am
Progress report:
I've set up four 74141s and two shift registers (595s), but am running two nixies so far, and a bulb.
I'm using a spare PC PSU for power, the arduino is the one I fried so it needs to be powered from USB.  I'll be adding a USB plug to the PSU as soon as I've been to maplin to buy a male type B plug.

Here's some pics:
Nixies:
(http://cowjam.co.uk/arct/nixie2.jpg) (http://cowjam.co.uk/arct/nixie2_big.jpg)
Click for Big.

The rig (using a bit of Meccano to make a gantry to hold the nixies):
(http://cowjam.co.uk/arct/nixie1.jpg)

Top view:
(http://cowjam.co.uk/arct/nixie3.jpg) (http://cowjam.co.uk/arct/nixie3_big.jpg)

At the top is the 12v - 180v PSU.
Coming in on the right is a 5v line and a 12v line from the PSU.
The breadboard is 74141, 74141 and 595 (in use) and the same again waiting to be hooked up and an IN-35 bulb.
The arduino is sat on a bit of polystyrene and attached to the gantry.
The nixies are in sockets suspended from the gantry.
Title: Re: Nixies: stupid questions.
Post by: FEDERICO on Jan 31, 2011, 12:33 am


Are the Mps42A switching the anode?

Why do you want to switch the anode?


I am getting a bit confused.
You guys said that optocouplers are not necessary if I am going to multiplex the nixies.
In your setup aren't necessary because you hook up the anode and use a 74hc595 with two 74141 for 2 nixies. So if you have 6 nixies you have 3 595 and 6 74141, at least.

But, if you, for example, connect all the cathodes of your nixies together to a single 74141 you need to switch the anodes with the 595, in high voltage multiplexing them and using persistence of vision. I supposed that this was the meaning of the transistor, for dividing the high voltage of the nixies from the low voltage of the IC's and the arduino...

Fede
Title: Re: Nixies: stupid questions.
Post by: cowjam on Jan 31, 2011, 12:44 am
I understand, it's my mistake. Sorry for confusing you!
Title: Re: Nixies: stupid questions.
Post by: wyager on Jan 31, 2011, 02:51 am

Are the Mps42A switching the anode?


MPSA42s to switch the cathodes, and MPSA42+MPSA92s to switch the anodes. Look at the bottom of http://sites.google.com/site/willyager/nixie-clock .


Cowjam, I'm glad you've gotten it working. Looking very cool!
Title: Re: Nixies: stupid questions.
Post by: cowjam on Feb 01, 2011, 12:47 am
Wow, I thought mine was complicated! I've just finished adding the second two nixies, using a breadboard and jumper wires is a nightmare. It's like playing kerplunk in reverse.

I've also added a rotary encoder for changing the numbers.

(http://cowjam.co.uk/arct/nixie4.jpg)
Title: Re: Nixies: stupid questions.
Post by: wyager on Feb 01, 2011, 01:13 am
Wow-lots of wires! Thankfully, the IN-14s I'm using (as soon as USPS feels like delivering them, they've been in the US since at least the 26th) come with long leads, so hopefully it will just be plug-and-play.
Title: Re: Nixies: stupid questions.
Post by: cowjam on Feb 01, 2011, 01:28 am

Wow-lots of wires! Thankfully, the IN-14s I'm using (as soon as USPS feels like delivering them, they've been in the US since at least the 26th) come with long leads, so hopefully it will just be plug-and-play.


Cool.  I had to solder leads onto the sockets.  There's four 74141s and two 595s on my breadboard. I'm slightly amazed I got it all working pretty much first time (I'd got digits 8 and 9 mixed up on one of the nixies).  It'd have all been easier if I could make my own PCBs but that's something I've not got round to yet.
Title: Re: Nixies: stupid questions.
Post by: wyager on Feb 01, 2011, 02:20 am
It'd have all been easier if I could make my own PCBs but that's something I've not got round to yet.


I hear that... I've been wanting to make PCBs for a while now, but I've just never had the chance to get the chemicals or copper board (at a reasonable price, at least).