I agree with Bill. I like a low part count.. the lower the part count the greater the ultimate reliability.
The diode drop is a good idea and is what I used along with PWM of high power '595 shift registers. I thought about adding a separate DC-DC converter for just the tubes.. but that would have been another half dozen parts, and it's not 100% efficient, so it would not have saved too much power vs just a plain old diode burning off some voltage. I'm going to definitely try to see if I can keep the segments warm in software, as everyone agrees the thermal shock of constantly changing segments is not ideal. A side by side test of some overdriven tubes, one with warm segments and one without, may be an interesting test. Regards, -Moses On Tuesday, March 7, 2023 at 8:09:08 AM UTC-8 [email protected] wrote: Not as easy as that sounds. If you want to use software (I presume PWM) you cant use a 4511 anymore since their greatest advantage (besides the BCD to 7 segment decoding) is its latch function. No way to implement any software based dimming. This would require a very drastic hardware redesign. Turning the 5V line down would work, but may cause issues with the rest of your circuit. A dedicated supply for the 4511’s could work, but depending on the final setting, there would be a discord in logic levels between the rest of the circuit and the 4511. Nasty, could result in unreliable communications. Level shifters could fix that, but wow, we are getting complicated again. The diode is still the best solution in my mind. Working with silicon and Schottky diodes you can obtain steps of 0.3V, 0.6V, 0.9V, 1.0V, 1.2V etc. Some diodes have slightly different forward voltage drops, so with a bit of searching you can obtain a lot of very simple options. Using jumpers of DIP switches you can even make it very simple to adjust. Why all the complicated solutions? Bill v *From:* [email protected] <[email protected]> *On Behalf Of *Batareyka *Sent:* Tuesday, March 07, 2023 10:19 AM *To:* neonixie-l <[email protected]> *Subject:* Re: [neonixie-l] Re: IV-9 numitron lifespan There are two ways to solve this problem. 1. Software, but as the author of the topic, there is no software and the possibility of editing it (I I think so), then method number 2 remains. 2. The 4511 chip has a wide power supply range from 3-16 volts. Put the power regulator and turn it up to 4 volts, which will change the output power of the lamp filaments accordingly. Checked more than once. вторник, 7 марта 2023 г. в 17:02:08 UTC+2, [email protected]: Martin, How did you do that? (schematic) Problem with a pot (or any resistor) is that you would need one for each element (7 per tube) since you cannot put one in the common line. Each filament draws about 22mA, so depending on the number displayed, the current would be anywhere between 44 and 154 mA. This would result in different voltage drops depending on the number displayed. It would result in uneven light output. Same reason why you could not use a single current regulator pre tube, but one per filament would be needed. A voltage regulator (such as a simple diode) does not have that disadvantage. Bill v *From:* [email protected] <[email protected]> *On Behalf Of *martin martin *Sent:* Tuesday, March 07, 2023 9:09 AM *To:* [email protected] *Subject:* Re: [neonixie-l] Re: IV-9 numitron lifespan How about this clock I built in the early 80s? 5314 clock chip. I used a 1k pot for dimming. Has been running for many moons now! ~ *[email protected]* On Tue, Mar 7, 2023 at 5:55 AM gregebert <[email protected]> wrote: 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 [email protected] 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:* [email protected] <[email protected]> *On Behalf Of *gregebert *Sent:* Monday, March 06, 2023 8:13 AM *To:* neonixie-l <[email protected]> *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 [email protected] 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:* [email protected] <[email protected]> *On Behalf Of *Chris *Sent:* Saturday, March 04, 2023 8:19 AM *To:* neonixie-l <[email protected]> *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 [email protected] 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 [email protected]. 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