Why is multiplexing nixie's bad

[dr pepper]

So why is multiplexing a bad idea, and static displays make tubes last
longer?, does multiplexing accelerate cathode poisoning or something?
I have 3 or 4 prototypes I've put together and they all use
multiplxing, even the single tube ones use pwm as a brightness control
(and so probably inherit the 'bad habits' too).

[Adam Jacobs]

I don't think that multiplexing is a bad idea.. On the contrary, it should extend the life (provided that you don't drive the tubes at more current than they are rated for). That's the key, really.. I think that most people drive the tubes at significantly higher than rated currents when they multiplex so that the brightness is higher.

If I run 6 IN-12 nixies at 2.5ma each in a 1x6 mus, then I would assume that the tubes would last 6x as long as they would in a direct-drive configuration.

-Adam

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[David Forbes]

Multiplexing itself isn't bad for the tubes, but it requires higher
drive current to achieve the same brightness level, since each tube is
illuminated for a small percentage of the time. Therefore, a multiplexed
display of a particular brightness will not last as long as a
direct-drive display of the same brightness.

On the other hand, Nixie tubes were designed for scientific equipment in
office or lab environments. Direct drive at the recommended current
level can be excessively bright for typical home lighting environments.

The choice is best made based on the desired brightness level of the
display.

--
David Forbes, Tucson AZ

[Adam Jacobs]

For in the bedroom, I find the 1x6 mux (at standard current) to be of acceptable brightness. On the contrary, a 1x6 mux VFD clock that I built is _way_ too bright for the house (like you can't sleep for the blue glow). I took the VFD clock to the office and it looks fine there.

Relative brightness is a relative thing.

-Adam

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[threeneurons]

Other than brightness, some have observed mechanical 'singing' coming off the larger tubes, like IN-18s. If the multiplexing frequency is too close to the mechanical resonating frequency, of the tubes, you may hear the tube buzzing. That usually can be remedied by altering the frequency. And only a small amount. Change it too much, and you'll jump on top of a harmonic (multiple) of the resonant frequency, which is almost as bad. Plus you'll have to find those numbers, experimentally.

Oh, and if you pick too low of a multiplexing frequency, you'll see them flicker. But then again, can easily be remedied by increasing the frequency. Of course, if the frequency is too high, the tubes won't have enough time to turn-ON. But there's a wide range between flicker (low) and turn-ON (hi) issues.

All the clocks, I've made, are multiplexed. No problems, and some of them are approaching 10 years of operation. Only problem, I've had, was choosing the IN-4, on my first clock. Those are not mercury enhanced, hence need to be replaced periodically.

 

[Dan Hollis]

On Thu, 20 Sep 2012, threeneurons wrote:
> Other than brightness, some have observed mechanical 'singing' coming off
> the larger tubes, like IN-18s.

This is the most annoying thing about multiplexing. You can hear the in-18
tubehobby kit singing from across a room.

Anyone delling direct drive in-18 kits?

-Dan

[Jeff Thomas]

Pro's: Reduced component count.

Cons: Significantly reduced brightness in comparison to direct drive at equal cathode current.  Visible flicker- like POV, accentuated at periphery of vision.  Audible noise, or buzzing.


PWM with direct drive is also a common feature of many clock designs to control display brightness.


Regards, Jeff







 

[David Forbes]

On 9/20/2012 10:37 AM, Jeff Thomas wrote:
>
>
> On Wednesday, September 19, 2012 6:39:22 PM UTC-7, dr pepper wrote:
>>
>> So why is multiplexing a bad idea, and static displays make tubes last
>> longer?, does multiplexing accelerate cathode poisoning or something?
>> I have 3 or 4 prototypes I've put together and they all use
>> multiplxing, even the single tube ones use pwm as a brightness control
>> (and so probably inherit the 'bad habits' too).
>>
>
> Pro's: Reduced component count.
>
> Cons: Significantly reduced brightness in comparison to direct drive at
> equal cathode current. Visible flicker- like POV, accentuated at periphery
> of vision. Audible noise, or buzzing.

Flickering is not an issue if the refresh rate is high enough. The audible noise
is subject to the tube itself, so it may or may not be present. The clocks that
I built had neither of these problems. And I set the display brightness to that
which would result in the same tube lifetime as a direct drive display, which is
about twice the direct drive current for a 1/6 duty cycle display.

The main disadvantage of a multiplexed display is that you have to worry about
those details, and other details such as ghosting of adjacent digits. So it's a
technique best used by more advanced clock builders willing to take the time to
learn about and solve the problems that may crop up.


--
David Forbes, Tucson, AZ

[Adam Jacobs]

You forgot the other pro's:

- reduced power consumption
- dramatically increased tube life at equal cathode current.



--
The point is that there isn't a "right" answer or a religious opinion. To multiplex or not is really a design decision which should be made based on your product requirements. I own (and have designed) both multiplexing and non-multiplexing clocks. I tend to lean towards multiplex for the "cheap & easy" clocks and towards direct-drive (with cross-fade PWM, etc) for the "deluxe" clocks.. but to each their own. In the case of VFD clocks, I can heartily recommend multiplexing. The fact that VFD's are triodes makes multiplexing a breeze.. and they are so bright anyways, I can't imagine what they would look like direct driven.

-Adam

On 9/20/2012 10:37 AM, Jeff Thomas wrote:

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[jb-electronics]

Hi there,

> On Thu, 20 Sep 2012, threeneurons wrote:
>> Other than brightness, some have observed mechanical 'singing' coming
>> off
>> the larger tubes, like IN-18s.
>
> This is the most annoying thing about multiplexing. You can hear the
> in-18 tubehobby kit singing from across a room.

might also be the switch mode power supply. I have a couple of small
power supplies from TaylorEdge who are remarkably loud.

> Anyone delling direct drive in-18 kits?

Take a look at Dieter's IN-18 Blue Dream masterpiece:
http://www.nixiekitworld.com/

Best regards
Jens

[Adam Jacobs]

I've definitely used a few inductors that buzzed nastily before. The
sound of a coil contracting around a ferrite repeatedly.
That's one advantage of using one of those ugly acrylic box cases. :)
Great at noise dampening.

-Adam

[Dan Hollis]

The ringing is coming directly from the tubes.

-Dan

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[Jeff Thomas]

You forgot the other pro's:

- reduced power consumption
- dramatically increased tube life at equal cathode current.

-Adam

Right you are! :))

Here's a few more to support your posts:

- Less weight.
- Fewer calories.
- Smaller Carbon footprint.

Although in fairness, since were nitpicking here; you could make your tube life comparison of operating at equal cathode current to direct drive, to include the penalty of substantially reduced brightness.

Regards, Jeff

[Adam Jacobs]

That was my point, really, I was trying to stay in the same reference frame as your post. Given equal cathode current in both cases, the multiplexed device will have lower brightness and greater tube life. Given equal cathode current, the direct driven device will have higher brightness and reduced tube life.

-Adam W7QI

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[jf...@my-deja.com]

On Sep 20, 11:24 am, jb-electronics <webmas...@jb-electronics.de>
wrote:

> Hi there,
>
> > On Thu, 20 Sep 2012, threeneurons wrote:
> >> Other than brightness, some have observed mechanical 'singing' coming
> >> off the larger tubes, like IN-18s.
>
> > This is the most annoying thing about multiplexing. You can hear the
> > in-18 tubehobby kit singing from across a room.
>
> might also be the switch mode power supply. I have a couple of small
> power supplies from TaylorEdge who are remarkably loud.
>

I have some old B-7971 clocks that are use 1x6 multiplexing at about a
2kHz rate. Even though they are completely enclosed in cabinets
madeof 1/4" plexiglass, you can hear them singing up to 10' away in a
quiet room. The high speed switching of the high voltages also
produces a lot of RFI on the AM and SW bands. It could not be
switching noise from the power supplies because these clocks have
linear power suppplies, the noise (singing and RFI) is at the mux
rate, and you can hear that it is it coming from the tubes.

The clocks have all been running 24/7 for more than 35 years, so if
mux'ing reduces the lifetime I have not seen it yet.

[seaforth23]

I reckon I am quids in here - I am 62 years old - and have had at least 2 direct drive clocks (Mike Harrison design) running continuasly for over 20 yrs now - I can't see any deterioation in brightness. But maybe my eyes are not as good as they used to be. I have built a 6 digit multiplexed B7971 clock which you could here singing in a quiet room - but i regarded  that as a "feature" not an annoyance. But then my hearing is probably not as good as it used to be.  I reckon the clocks I make now (given the average human lifetime) will be safe with either type of drive!

[kay486]

I have a multiplexed Z566M clock and it makes quite a lot of noise. I think tha the noise is produced by the cathodes, because they arent completely fixed in place by the spacer rings, so they tend to buzz when they are multiplexed. Thats just my guess though.

On Thursday, 20 September 2012 02:39:22 UTC+1, dr pepper wrote:

[John Rehwinkel]

> I reckon I am quids in here - I am 62 years old - [...] I reckon the clocks I make now (given the average human lifetime) will be safe with either type of drive!

I have some good news for you. The oft-quoted "average human lifetime" is from birth, and includes all those people that die young. However, you weren't
just born, you're past all that stuff. Which means the "average human lifetime" no longer applies to you. People that have made it to 50 can't die younger than
50, so their entire distribution is pushed forward. The average age of death for living 50-year-olds is much higher than the average age of death of newborns.
At 62, this applies more strongly. Granted, not many people make it to 150, but a fair chunk of us older folks can expect to see our hundredth birthday.

- John

[Instrument Resources of America]

Does this mean that I have more time too?? This is definitely good news
John as I'm over 60. Lets celebrate, I want a beer!!!!!!!! LOL Ira.

[Tidak Ada]

The noise made by coils may easily be reduced by the use of PlastiDip®

 

eric

---

From: neoni...@googlegroups.com [mailto:neoni...@googlegroups.com] On Behalf Of kay486
Sent: donderdag 20 september 2012 22:57
To: neoni...@googlegroups.com
Subject: [neonixie-l] Re: Why is multiplexing nixie's bad

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[dr pepper]

Well it seems my original post caused some interest.
I was aware of the brightness issues, its a similar story with leds.
I've messed around with 4 or 5 types of tube but never got any audible
sounds from them, I have with switching supplys, but later designs I
use are 30kc and up, I've just been messing with a minimal boost
supply that generates 200v from 5v and the drive waveform comes
straight off the microcontroller, I even have a brighness control
built in the software.
To conclude then it sounds like there is no major issue with muxing
tubes, so long as there isnt so many tubes that the current has to be
wound up so much that the tubes max isnt exceeded.
I'll remember this and if I decide to have a load of tubes on display
then I'll probably still multiplex them but in groups rather than an
entity.

On 20 Sep, 23:07, "Tidak Ada" <offl...@zeelandnet.nl> wrote:
> The noise made by coils may easily be reduced by the use of PlastiDipR
>
> eric
>
>   _____

[Terry S]

On Sep 20, 5:07 pm, "Tidak Ada" <offl...@zeelandnet.nl> wrote:
> The noise made by coils may easily be reduced by the use of PlastiDipR
>

I don't think I'd use PlasticDip. It has a distinct solvent odor.

We used to use beeswax for flyback transformers. Give that a try.

Terry

[Adam Jacobs]

I've also seen hot-glue used, especially if the potting is to lower RF
noise.
I'm a big fan of hot glue. I don't know where I first heard the
expression "Non-conductive solder", but I've latched onto it happily.
I also like that it easily dissolves in acetone.

-Adam

[Jan Rychter]

On 20 wrz 2012, at 19:50, Adam Jacobs <ad...@jacobs.us> wrote:

[about multiplexing]

> You forgot the other pro's:
>
> - reduced power consumption
> - dramatically increased tube life at equal cathode current.

Ok, so has that actually been proven? I've seen opinions stating that tube life is dramatically increased and others saying that it is dramatically reduced. Some people say it has no influence at all. I'd really like to see a definitive (e.g. fact- or reasoning- based) statement on the matter.

Anyone?

--J.

[fixitsan]

It is clear that the statement was correct, considering it quoted "at equal cathode current"
 
So take one nixe and turn it on , direct drive for 24 hours
Take another in a 1:4 mux which runs for 24 hours. in this muxed case each tube is only on for 1/4 of the 24 hours. Therefore , where the cathode current is the same in a muxed clock as for a direct drive clock, the tubes in the muxed clock  must experience lower utilisation levels, individually speaking.

Tube life is a function of cathode current (until the current is so low that poisining could occur). That suggests something of a relationship between lifetime and power dissipation. In many muxed designs the cathode current is increased and therefore the nixie lifetime would be reduced if the tube was always on. However, in a 1:6 mux although the tube is dissipating more power due to the higher current, it is only active for 1/6th of the time of an equivalent direct drive tube.

I have seen several good statements made here, backed up with good theory, which suggests that a doubling of cathode current in a 1:4 or 1:6 clock doesn't affect tube lifetime when compared to a direct drive design using lower current, which didn't appear to bring about any controversy.

Personally, I've run a 1:6 mux with 2.2 times rated current and a 2:3 mux with 1.6 times rated current, as well as a 1:2 mux (2 tube clock) with a 1.4 current multiplier. All clocks were sufficiently bright for normal viewing in a well lit room. Lifetime seems to not have been affected. There were early scare stories about reduced lifetimes when datasheet lifetime figures were considered sacred, but they all seem to have been false.

The noise is often due to mechanical movement, I think it is caused by electrostatic effects. I noticed in one clock which sufferedd badly that when I changed the design so that instead of letting 'off' cathodes float they were instead tied to a mid level voltage of about 90 Volts, via a 'pull mid' resistor, that the noise was reduced. That might confirm that floating cathodes adopt a high floating voltage which is quickly removed when it is pulled to ground and that causes the electrostatic deflection. By reducing the energy which needs to be discharged the movement, and therefore the sound, is also reduced.

Chris

[dr pepper]

That answers a few points.
So overdriving tubes isnt necessarily a no no.
I also didnt know poisoning occurs at too low a current, better put a
minimum brightness limit on any new designs then.
I have a dekatron circuit that uses 'pull mids', it works without
them, I was wondering why they were there, I think your comments
answer that question.

On 21 Sep, 10:24, fixitsan <chefin...@gmail.com> wrote:
> On Friday, September 21, 2012 9:27:18 AM UTC+1, Jan Rychter wrote:
>

> > On 20 wrz 2012, at 19:50, Adam Jacobs <ad...@jacobs.us <javascript:>>

> Chris- Hide quoted text -
>
> - Show quoted text -

[Bill van Dijk]

A lot of the discussion here about multiplexing is in generalities. I use a
number of Burroughs B5750 tubes (who have miraculously survived more than 30
years of clean-up attempts from the ball and chain :-)) and their
documentation specifically states that this tube is designed for time share
applications, and even provides data for increased anode currents at
different duty cycles.

Since some tubes do not have that information, I would suspect they were not
specifically designed with multiplexing in mind. This of course does not
mean it would be bad for them I suppose.... Any of the tubes I multiplexed
did not complain, although some did not like a 1-6 multiplex in the sense
that there were brightness issues and some ghosting issues to be resolved.
I have not had any noise issues from the tubes, but I use mostly small tubes
that may be less susceptible.

Bill van Dijk

> -----Original Message-----
> From: neoni...@googlegroups.com [mailto:neoni...@googlegroups.com]
> On Behalf Of dr pepper
> Sent: Friday, September 21, 2012 10:10 AM
> To: neonixie-l
> Subject: [neonixie-l] Re: Why is multiplexing nixie's bad
>

[Adam Jacobs]

I believe that the "singing" issue is primarily a problem with larger
nixie tubes, of which I have no (as of yet) experience. I've never had a
problem with singing tubes with IN-12, IN-14, IN-8, IN-8-2, IN-16, IN-17
tubes.. but these are pretty small tubes (18mm digit height or less).
never had a problem with ghosting either, but the IN-12's in a 1x6 are
definitely lower brightness with a very slight flicker that is only
noticeable from the edge of the eye. There is a very distinct "look" to
the 1x6 mux, so I use it only for my lowest-end clocks. If I'm
interested in how it looks, I'll use a 2x3 mux or direct drive. To my
eye, the 2x3 mux looks a LOT better tan 1x6.

-Adam

[dr pepper]

Interesting pojt Bill on the fact that some data sheets specify
multiplexing and some dont, as you say some tubes were not 'desgined'
to be muxed, I think thats probably because muxing wasnt common when
nixies were current, I wonder what manufacturers did to a tube to make
it intended for muxing, or whether its just a new spec applied to an
old design.

I really dont spose I'm going to know without trying if lifecycle is
greatly reduced without trying it myself, one thing encouraging is
that there are folks that have clocks with muxed tubes that have been
going for years, and theres no mention of anyone with a clock that
munches tubes every 10 minutes.

> >> question.- Hide quoted text -