Author Topic: EEVblog #948 - Nixie Tube Display Project - Part 1  (Read 67172 times)

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Offline calexanian

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Re: EEVblog #948 - Nixie Tube Display Project - Part 1
« Reply #50 on: November 30, 2016, 11:17:28 pm »
The only potential problem with this sort of arrangement, and I will use this particular example, is that since you now only effectively have 48 volts differential between your on and off state you have to ensure that the high voltage supply is now enough in voltage that they will completely shut off the numerals when the open collector conducts, but high enough that they will start and come to an acceptable level of illumination. Nixies have a bad habit of changing characteristics as time goes on.
Charles Alexanian
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Offline alank2

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Re: EEVblog #948 - Nixie Tube Display Project - Part 1
« Reply #51 on: December 01, 2016, 02:23:32 am »
One day I'd love to do a nixie project - I have one question:

Is there a cathode poison prevention method that can be done quickly as to not be visible?
 

Online NivagSwerdna

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Re: EEVblog #948 - Nixie Tube Display Project - Part 1
« Reply #52 on: December 01, 2016, 10:42:12 am »
FWIW the physical design might be interesting too... for example some more modern designs have each tube on a daughter board which is pluggable.. the advantage being that they can be soldered, tested, replaced etc separately...
 

Offline EEVblog

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Re: EEVblog #948 - Nixie Tube Display Project - Part 1
« Reply #53 on: December 01, 2016, 10:48:51 am »
Although, I'm still not a huge fan of these ULN things.
They are just simple 'crude' driver units, that act as an extra buffer.
This means that you still need heaps of I/Os OR a shift register.
In the end you don't win much at all compared to just a few transistors.

Not so.
a) You still need the shift registers unless you have 88 I/O pins available on your micro
and
b) You need 88 transistors + 88 resistors if using BJT

I'd rather have 13 ULN2003's + zeners instead of 88 transistors and resistors.
The ULN2003 combine the transistor and the base resistors in a nice easy to solder package.
A better solution IMO.
 

Offline bktemp

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Re: EEVblog #948 - Nixie Tube Display Project - Part 1
« Reply #54 on: December 01, 2016, 10:57:02 am »
I'd rather have 13 ULN2003's + zeners instead of 88 transistors and resistors.
The ULN2003 combine the transistor and the base resistors in a nice easy to solder package.
A better solution IMO.
Even better: TPIC6A595/TPIC6B595
8bit shift register + 8 channel 50V driver + 50V clamp in one package.
http://www.ti.com/product/TPIC6A595
http://www.ti.com/product/TPIC6B595
 

Offline alank2

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Re: EEVblog #948 - Nixie Tube Display Project - Part 1
« Reply #55 on: December 01, 2016, 01:19:18 pm »
I realize the goal is to use easily obtainable parts, but the nixies themselves are not something you can easily order anyway.  Why not consider the nixie, its socket, and its driver IC all to be in the same boat.  There are plenty of the driver IC's on eBay.  What are the pros and cons of using nixie drivers vs. coming up with a modern solution?
 

Offline Spuddevans

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Re: EEVblog #948 - Nixie Tube Display Project - Part 1
« Reply #56 on: December 01, 2016, 06:58:44 pm »
The only potential problem with this sort of arrangement, and I will use this particular example, is that since you now only effectively have 48 volts differential between your on and off state you have to ensure that the high voltage supply is now enough in voltage that they will completely shut off the numerals when the open collector conducts, but high enough that they will start and come to an acceptable level of illumination. Nixies have a bad habit of changing characteristics as time goes on.

You could always use SN75468N 's (pin for pin compatable with ULN2003's) which are rated for 100V and use 90V Zener.

Tim
 

Offline BU508A

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Re: EEVblog #948 - Nixie Tube Display Project - Part 1
« Reply #57 on: December 01, 2016, 10:50:46 pm »
Dave,

why not use one of these nice chips? They seem to me quite suitable for these Nixie tubes:

- HV6810 from microchip - Datasheet: http://ww1.microchip.com/downloads/en/DeviceDoc/20005626A.pdf
  It has 10 channel output, serial input, operating voltage up to 80V (End of life)

- HV5812 from microchip - Datasheet: http://ww1.microchip.com/downloads/en/DeviceDoc/HV5812%20C072413.pdf
  It has 20 channel output, serial input, operating voltage up to 80V

- HV518 from microchip - Datasheet: http://ww1.microchip.com/downloads/en/DeviceDoc/HV518%20C072413.pdf
  It has 32 channel output, serial input, operation voltage up to 90V

They are all available here:
Mouser:
http://www.mouser.de/Semiconductors/Driver-ICs/Display-Drivers-Controllers/_/N-7zhqdZscv7?P=1yzr6k5

Digikey:
https://goo.gl/z6Nzxu

Aliexpress:
https://www.aliexpress.com/wholesale?catId=0&initiative_id=SB_20161201144129&SearchText=HV6810
https://www.aliexpress.com/wholesale?catId=0&initiative_id=SB_20161201144208&SearchText=HV5812
https://www.aliexpress.com/wholesale?catId=0&initiative_id=SB_20161201144246&SearchText=HV518

On ebay are also several sources available.

Hope, you'll find this help-/useful.

Andreas
“Chaos is found in greatest abundance wherever order is being sought. It always defeats order, because it is better organized.”            - Terry Pratchett -
 
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Offline EEVblog

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Re: EEVblog #948 - Nixie Tube Display Project - Part 1
« Reply #58 on: December 01, 2016, 11:50:37 pm »
I'd rather have 13 ULN2003's + zeners instead of 88 transistors and resistors.
The ULN2003 combine the transistor and the base resistors in a nice easy to solder package.
A better solution IMO.
Even better: TPIC6A595/TPIC6B595
8bit shift register + 8 channel 50V driver + 50V clamp in one package.
http://www.ti.com/product/TPIC6A595
http://www.ti.com/product/TPIC6B595

I actually shot a clip of that chip in the original video but took it out of the final video to save time as I thought it was interesting but wasn't suitable due the 50V voltage. I didn't notice it had output clamps!
I think it's winner.
I'm just laying out the schematic now and just placed the ULN2003's, so good timing.
 

Offline calexanian

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Re: EEVblog #948 - Nixie Tube Display Project - Part 1
« Reply #59 on: December 01, 2016, 11:57:27 pm »
The only potential problem with this sort of arrangement, and I will use this particular example, is that since you now only effectively have 48 volts differential between your on and off state you have to ensure that the high voltage supply is now enough in voltage that they will completely shut off the numerals when the open collector conducts, but high enough that they will start and come to an acceptable level of illumination. Nixies have a bad habit of changing characteristics as time goes on.

You could always use SN75468N 's (pin for pin compatable with ULN2003's) which are rated for 100V and use 90V Zener.

Tim

That part looks like a good fit. Hey Dave! go look at those SN75468's. Not quite as cheap as the ULN2803 but the more I think about it I am not comfortable with that 48 volt window.
Charles Alexanian
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Offline Technics

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Re: EEVblog #948 - Nixie Tube Display Project - Part 1
« Reply #60 on: December 02, 2016, 03:26:35 am »
I have a clock on my desk at work and one at home that use the TPIC6B585. They have both been running for over 3 years so I dare day it's just fine used as a nixie driver.

Here's one:


And the other:


Looking forward to seeing what you are going to make with the 8 tubes.
 
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Offline firehacker

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Re: EEVblog #948 - Nixie Tube Display Project - Part 1
« Reply #61 on: December 02, 2016, 06:18:19 am »
I'd rather have 13 ULN2003's + zeners

Funny, this was my first thought when I finished watching Part 1. Then I asked myself: why Dave didn't mentioned this approach? There must be some issue with that. And then I realized what could be wrong with that.

As far as I understand the physics of gas discharge tubes, you have a sort of hysteresis there. To start conduction you need to apply voltage greater than firing voltage (which is 170V for these particular tubes). Than the conduction won't stop until voltage drops below minimal sustaining voltage (which is guaranteed to be not less than 120V according to the datasheet).

Unfortunately, this window (170V – 120V = 50V) is the same as ULN2003 max voltage and therefore is equal or even greater than our clamping voltage.

So, it is possible, that since we "fired" a digit in the tube, we will not be able to turn it off just by switching off corresponding channel of ULN, isn't it?

I mean that when using clamping approach, you are limited to have either 0V or 48.6V on a cathode pin of the tube so that voltage drop is either 170V or 121.4V, and the lowest one is above the minimal guaranteed  turn-off threshold.
« Last Edit: December 02, 2016, 06:33:27 am by firehacker »
 

Offline bktemp

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Re: EEVblog #948 - Nixie Tube Display Project - Part 1
« Reply #62 on: December 02, 2016, 07:16:05 am »
I'd rather have 13 ULN2003's + zeners instead of 88 transistors and resistors.
The ULN2003 combine the transistor and the base resistors in a nice easy to solder package.
A better solution IMO.
Even better: TPIC6A595/TPIC6B595
8bit shift register + 8 channel 50V driver + 50V clamp in one package.
http://www.ti.com/product/TPIC6A595
http://www.ti.com/product/TPIC6B595

I actually shot a clip of that chip in the original video but took it out of the final video to save time as I thought it was interesting but wasn't suitable due the 50V voltage. I didn't notice it had output clamps!
I think it's winner.
I'm just laying out the schematic now and just placed the ULN2003's, so good timing.
Why are you using TPIC6C595 (in your component library drawing video)? They have a breakdown voltage of only 33V instead of 50V for A and B variants and have a different pinout!
 

Offline TheRevva

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Re: EEVblog #948 - Nixie Tube Display Project - Part 1
« Reply #63 on: December 02, 2016, 08:53:38 am »
UPDATE: The totom pole output driver isn't work too great. Will cover this in the next video.
Just out of interest Dave...
What happens if you leave the VPP (HV) input pin of the totem pole driver floating rather than holding it at some specific value?
(Thereby effectively only using the lower half of each totem pole output).
It would at least be an interesting test
 

Online NivagSwerdna

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Re: EEVblog #948 - Nixie Tube Display Project - Part 1
« Reply #64 on: December 02, 2016, 05:43:17 pm »
I'm struggling to reconcile some of the things I have seen in the videos with some of the things I have read in the past and am assuming this is due to lack of understanding on my part... i.e. an impedance mis-match.

The videos show a fail with a totem pole driver (as found in HV5812) but we know there are solutions which work really well with that device.

I knocked up a quick model to show the state of the device when connected to a 'off' element floating at 120V and a HV5812 like device where VPP is supplied with around 60V from a resistor/zener combo attached to the HV 170V supply.

The crux seems to be the ability of the floating pin to supply current... but given the element is at a potential that is lower than that required to ionise the gap its ability to conduct must be limited...

Is that how it works?

In the diagram I've tweaked a few values (the reference being 62V) and added the 47k as an indication of something that doesn't conduct very well....
« Last Edit: December 02, 2016, 05:49:03 pm by NivagSwerdna »
 

Offline calexanian

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Re: EEVblog #948 - Nixie Tube Display Project - Part 1
« Reply #65 on: December 02, 2016, 06:29:08 pm »
Uh oh. The EEVBlog forum echo chamber is in full effect.

Tim mentioned the SN75468.

Permit me to go on a little rant.

That should have been the end of the selection conversation right there! Its cheap, has a common clamp, has easy drive requirements, and is made as a high voltage replacement for the ULN2003 type circuits. Nobody apart from me even mentioned that Tim found a completely practical suitable part that fits the requirements as laid out. I don't want to get into the psychological discussion of how technical people think but I hate to think what goes on in your design review meetings (assuming you actually work professionally. If not then still take it in the spirit intended) when good ideas and complete solutions are ignored for no apparent reason. This is a close cousin to going over the same design consideration over and over again and when a decision is made, you find yourself going over it again just a few days later and have to re convince everybody of what the solution was all the while wasting time and destroying morale.
Charles Alexanian
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Offline calexanian

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Re: EEVblog #948 - Nixie Tube Display Project - Part 1
« Reply #66 on: December 02, 2016, 06:33:14 pm »
I'd rather have 13 ULN2003's + zeners

Funny, this was my first thought when I finished watching Part 1. Then I asked myself: why Dave didn't mentioned this approach? There must be some issue with that. And then I realized what could be wrong with that.

As far as I understand the physics of gas discharge tubes, you have a sort of hysteresis there. To start conduction you need to apply voltage greater than firing voltage (which is 170V for these particular tubes). Than the conduction won't stop until voltage drops below minimal sustaining voltage (which is guaranteed to be not less than 120V according to the datasheet).


Unfortunately, this window (170V – 120V = 50V) is the same as ULN2003 max voltage and therefore is equal or even greater than our clamping voltage.

So, it is possible, that since we "fired" a digit in the tube, we will not be able to turn it off just by switching off corresponding channel of ULN, isn't it?

I mean that when using clamping approach, you are limited to have either 0V or 48.6V on a cathode pin of the tube so that voltage drop is either 170V or 121.4V, and the lowest one is above the minimal guaranteed  turn-off threshold.

Once again see Tim's recommendation of the SN75468. Its higher voltage rating helps this problem.

Also I love the Cardasian avatar. Is that Garak?
Charles Alexanian
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Offline firehacker

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Re: EEVblog #948 - Nixie Tube Display Project - Part 1
« Reply #67 on: December 02, 2016, 07:17:34 pm »
Once again see Tim's recommendation of the SN75468. Its higher voltage rating helps this problem.
I've seen it — good recommendation. To be honest, I haven't read the topic before posting my comment. After watching "Part 2" video I wanted to leave my comment there on YouTube, but than decided that it's too long for YouTube, so I went here and posted it here. Only after posting it I read the entire topic.

Another thing about my comment is that its goal is not to give a recommendation on a part to be used as driver, its all about why Dave did not highlighted "hysteresis problem" in his video.

Also I love the Cardasian avatar. Is that Garak?
Yep! It was taken from DS9: The Fallen.
« Last Edit: December 02, 2016, 07:34:34 pm by firehacker »
 

Offline Spuddevans

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Re: EEVblog #948 - Nixie Tube Display Project - Part 1
« Reply #68 on: December 02, 2016, 08:09:55 pm »
Uh oh. The EEVBlog forum echo chamber is in full effect.

Tim mentioned the SN75468.

I was unaware of this part, but when reading a datasheet for the ULN2003 it actually said for 100V use see the SN75468 (and SN75469 I think  :-\ )

Quote
I don't want to get into the psychological discussion of how technical people think but I hate to think what goes on in your design review meetings (assuming you actually work professionally. If not then still take it in the spirit intended) when good ideas and complete solutions are ignored for no apparent reason.

That's forum's for you, people will choose what to follow whatever they want to, and why not  :-// I am in the process of designing a Nixie Clock and had been going to use nearly 70 HV transistors and 70 resistors as a means for driving the Nixie's. Then after watching Dave's video and reading this thread I looked into the ULN2003's, that was when I read the datasheet and found the high voltage versions and am going with them now.

But everyone will choose what they want to use, I've been on enough forums (Forii??  :-// ) to realise that arguing my point of view gets me nowhere but feeling all riled up. If I can add to a discussion I will, but I'm not out to convince everyone I've got the best answer (cos usually I dont, and then I have to eat humble pie, and for those who've met me, I don't need to eat any more pies!!  :-DD )

Tim
 

Offline calexanian

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Re: EEVblog #948 - Nixie Tube Display Project - Part 1
« Reply #69 on: December 02, 2016, 09:28:08 pm »
The actor that played Garak was the bad guy in dirty harry.
Charles Alexanian
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Online NivagSwerdna

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Re: EEVblog #948 - Nixie Tube Display Project - Part 1
« Reply #70 on: December 02, 2016, 09:58:42 pm »
https://threeneurons.wordpress.com/nixie-power-supply/ is a very good read and mentions SN75468 and ULN2003 parts.  It also explains that the required voltage on the OFF cathodes to keep them from glowing is very much a function of tube size... this rabbit hole runs deep.
 

Offline Nobody2

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Re: EEVblog #948 - Nixie Tube Display Project - Part 1
« Reply #71 on: December 03, 2016, 09:24:05 am »
a) You still need the shift registers unless you have 88 I/O pins available on your micro
and
b) You need 88 transistors + 88 resistors if using BJT

I'd rather have 13 ULN2003's + zeners instead of 88 transistors and resistors.
The ULN2003 combine the transistor and the base resistors in a nice easy to solder package.
A better solution IMO.
I would suggest to use the ULN2803 instead of the 2003. So you "only" need 11 ULN's, shift registers and zeners.
 

Offline EEVblog

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Re: EEVblog #948 - Nixie Tube Display Project - Part 1
« Reply #72 on: December 03, 2016, 09:59:08 am »
Why are you using TPIC6C595 (in your component library drawing video)? They have a breakdown voltage of only 33V instead of 50V for A and B variants and have a different pinout!

They have clamping zeners built in.
It will have to be the 50V B series though, otherwise the digits would bleed on with the 30V C series.
« Last Edit: December 03, 2016, 10:39:39 am by EEVblog »
 

Offline alank2

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Re: EEVblog #948 - Nixie Tube Display Project - Part 1
« Reply #73 on: December 04, 2016, 02:02:46 am »
I was reading a page about nixies and have a few questions.

#1 - One page mentioned something about AC power - can nixies be driven with an ac?

#2 - I read that is isn't wise to have it turned off - maybe this was a reference to older nixie type drivers though.  With a newer style higher voltage driver with zener's like has been talked about here, is it ok to have all segments off?

#3 - What is the best way to have an adjustable brightness for nixies?  Given you have a fixed resistor to limit current...

Thanks!
 

Offline alank2

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Re: EEVblog #948 - Nixie Tube Display Project - Part 1
« Reply #74 on: December 05, 2016, 04:44:26 pm »
Anyone have any thoughts about my questions?
 


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