Under "normal" circumstances, I agree that individual current regulators add a lot of circuitry. The reality is that most tubes are no longer manufactured, so their numbers are dwindling as the price increases, essentially irreplaceable. You wouldn't believe the lengths I went towards protecting NIMO tubes in the clock I'm still working on.
I've debated about building a numitron clock, and the route I think I will go with uses LED 'filaments' that are used in retro light bulbs. Filaments scare the heck out of me because they will fail from thermal cycling, but there is no alternative for NIMO and VFD displays. On Monday, March 6, 2023 at 11:35:22 AM UTC-3 theoldpha...@gmail.com wrote: > Using a current limiter sounds like a LOT of circuitry, 7 times the number > of tubes? I simply use a forward biased diode to drop the voltage, about > 0.7 for a standard silicon diode, and about 0.3 for a Schottky. That > requires only one or perhaps two diodes for the whole set of tubes. Perhaps > not as accurate, but definitely a whole lot simpler. > > > > > > > > > > *From:* neoni...@googlegroups.com <neoni...@googlegroups.com> *On Behalf > Of *gregebert > *Sent:* Monday, March 06, 2023 8:13 AM > *To:* neonixie-l <neoni...@googlegroups.com> > *Subject:* Re: [neonixie-l] Re: IV-9 numitron lifespan > > > > Very good info, Moses. > > > > From that, I would target the operating current well-below 20mA to > prolong the life of the display. You could use an NPN current-limiter > (driver) driven from 5V TTL logic. Let me know if you need circuit details, > but it's a very simple design (1 NPN + 1 emitter resistor). As a starting > point, a 270 ohm emitter resistor will limit current to 16mA. > > > > Do you hear any noise with your PWM running at 1600Hz ? If not, I would > stick with PWM and not use the NPN driver, as it's not necessary. As long > as the PWM cycle-time is shorter than the thermal time-constant of the > filament (probably a few milliseconds), you should be fine. I think you can > measure the thermal time-constant of the filament with a phototransistor > and a scope. Starting at a low PWM frequency, the phototransistor will show > fluctuations in the bulb's intensity. As the frequency is increased, you > should see the amplitude decrease towards zero. I've never actually done > this but I'm pretty sure it will work. You have to use a phototransistor > (or photodiode); a CdS photosensor will have too-slow of a response time. > > On Monday, March 6, 2023 at 2:37:45 AM UTC-3 Moses wrote: > > The TI CD4511B datasheet lists the lists the *minimum* high level output > (at 5v VDD) of 4.1v but typical is 4.55v, maybe others are different? > > > > https://www.ti.com/lit/ds/symlink/cd4511b.pdf > > At 4.55v the segment current on the IV-9 is going to be about 25ma. > Typical IV-9 segment current is about 20ma I believe, so that would be a > 25% overdrive. > > > > I've put up a drive voltage vs segment current table on my site, maybe > it's useful to someone: http://www.neonixie.com/IV-9-6D-RR/#tech > > > > I settled with powering the tubes in my designs in one of two ways.. 5.0v > direct with a recommended PWM of about 65% (the 165 (out of 255) value in > the table) OR 5v through a regular silicon diode, dropping the voltage to > about 4.2v at the tube and PWM that to 76%. Both result in a segment > current of 20ma. Don't know if one or the other is better in regards to > lifetime, I was not able to find any official sources of information. I > experimented with driving them using a 3.3v regulator.. but at that voltage > they were a bit dim. > > > > NOTE: The IV-9 datasheet does mention to avoid running the tubes at a > frequency between 105 and 1000 Hz, presumably to avoid mechanical > resonance. I elected to run them at 1600 Hz. > > > > I looked through some of my testing data.. at a segment current of 3mA the > segments are visible, 2mA they are "barely visible" and at 1mA I noted them > as not visible. Keeping the unlit segments warm with a slight current seems > to make the most sense to me. It's all software on my clock so maybe an > option for the next revision. > > > > That's all I know so far. > > > > Regards, > > -Moses > > On Saturday, March 4, 2023 at 5:52:05 AM UTC-8 theold...@gmail.com wrote: > > Hi Chris, > > > > The numitrons are driven by a 4511 decoder, and according to their data > sheets the max. output at that voltage is 4.1 V, so that is well within > specification for the tube. Yes, I agree, lowering the voltage even further > should increase lifespan. > > > > Bill v > > > > *From:* neoni...@googlegroups.com <neoni...@googlegroups.com> *On Behalf > Of *Chris > *Sent:* Saturday, March 04, 2023 8:19 AM > *To:* neonixie-l <neoni...@googlegroups.com> > *Subject:* [neonixie-l] Re: IV-9 numitron lifespan > > > > Hi, > > While i am not sure for the IV9 numitrons have a look at the DA2300 > lifetime expectancy, > > > > Basically reducing the voltage increases the life expectancy > exponentially. > > So i usually run my numitrons at 4.5V or lower and have had no issues so > far. > > On Friday, March 3, 2023 at 8:05:48 PM UTC+1 theold...@gmail.com wrote: > > I seem to recall there was some discussion on the life expectancy of IV-9 > numitrons some time ago. > > > > In 2015 I built a number of clocks with these tubes, and they started > failing last year. The clock in the picture is on my bench now, the three > good tubes were replaced in November last year. So today all 6 tubes will > be replaced. I have replaced all 6 tubes on a few other clocks also. One or > more segments will no longer light up, and I do not see any blackening of > the glass tube (The black you see in the picture is my permanent marker, s > I will not replace the wrong tube when I disconnect the power). > > > > The tubes are driven directly from a 4511 chip on a 5V power line. > > > > There does not seem to be any order in which they fail, so I do not have > the feeling that any of the tubes are significantly impacted by thermal > stresses from flashing on and off. I would say based on my experience with > them, the expected lifespan is about 7 years of continues use. > > > > Bill v > > -- > You received this message because you are subscribed to the Google Groups > "neonixie-l" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to neonixie-l+...@googlegroups.com. > To view this discussion on the web, visit > https://groups.google.com/d/msgid/neonixie-l/81b5b7e6-d476-4b83-9a8e-c9d6cc468db9n%40googlegroups.com > > <https://groups.google.com/d/msgid/neonixie-l/81b5b7e6-d476-4b83-9a8e-c9d6cc468db9n%40googlegroups.com?utm_medium=email&utm_source=footer> > . > > -- > You received this message because you are subscribed to the Google Groups > "neonixie-l" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to neonixie-l+...@googlegroups.com. > > To view this discussion on the web, visit > https://groups.google.com/d/msgid/neonixie-l/13ceb519-9b4d-469e-9e03-8d844e317239n%40googlegroups.com > > <https://groups.google.com/d/msgid/neonixie-l/13ceb519-9b4d-469e-9e03-8d844e317239n%40googlegroups.com?utm_medium=email&utm_source=footer> > . > -- You received this message because you are subscribed to the Google Groups "neonixie-l" group. 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