I got around to adding a "keep warm" function for unlit segments on my IV-9 clock kit. My experiences and a short video for those interested.
I thought this would be a quick and easy modification.. it was anything but! I added a hardware interrupt at 1600hz, and added code to keep unlit segments warm with about a 1/10 duty cycle. Worked well.. but seemingly random reboots of the ESP32 micro drove me nuts, I chased a non-existing software bug for more then an hour (much more). Later (much later!) I realized that the load imposed by largish changes in brightness, either on power up or a commanded brightness change, combined with the keep warm function was a pretty big load on the power supply. Yes, even higher then just turning all tubes and segments on all at once. I tried different power cables, different clocks, half a dozen different power supplies from boat anchor linears to modern switchers, I was able to trip up all of them. I even have a very low ESR polymer cap on the clock as well, but nope, the spike load was just too much. My conclusion is the first few moments of the keep warm feature at 1/10 duty cycle, on 6 tubes and all segments, is a greater load then just turning on all segments normally. I'll have to hook up some proper equipment to quantify this soon. I could have brute force fixed this in hardware by throwing a bunch of caps at it.. but I went with the more elegant software solution. The brightness is no longer directly controlled, but ramped up and down (on bootup too) to match the requested brightness, this fixed the problem entirely. With a normal lit segment being driven at 20mA, the 1/10th duty cycle gives the unlit segments approx 2.5mA current, which is barely visible. I provided a user adjustable setting for the duty cycle, but having no official manufacturer guidance to go on I think 2.5mA is as good a default value as any. I hope this saves someone 4 hours of profanity ridden shaking of fists at a clock. Side note, while I was in there.. I added cross fading on the digits, which I must admit looks better then I had imagined on a numitron clock. See the video and be well! https://youtu.be/dkOwaZvVQrg Regards, -Moses On Wednesday, March 8, 2023 at 3:08:56 AM UTC-8 gregebert wrote: > Very interesting. Others who have multiplexed nixie tubes, which run at a > lower current, have reported audible noise. I would expect more noise at > higher currents due to magnetism effects, but that isn't happening here > with your numitrons. I've heard it myself with incandescent bulbs; I havn't > done any work with numitorns. > > On Tuesday, March 7, 2023 at 6:00:25 PM UTC-3 Moses wrote: > >> Gregebert, >> >> I've not heard these tubes at all. I was initially running them at 100Hz, >> then changed to 400Hz for a while before settling at 1600Hz. >> I've got half a dozen prototypes running for several months, so if they >> were going to make noise I would have heard them by now. >> >> Neat idea on measuring the time-constant, I'll give it a try. >> >> Regards, >> -Moses >> >> On Monday, March 6, 2023 at 5:12:55 AM UTC-8 gregebert wrote: >> >>> 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]. >>>>> 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 [email protected]. To view this discussion on the web, visit https://groups.google.com/d/msgid/neonixie-l/8f19bb63-0573-4ddd-88da-b66fc267af3en%40googlegroups.com.
