Thanks! That's alot of positive information - it seems that numitrons are indeed sturdy devices and they do not need that much protection as I thought. What is the frequency of the dimming PWM? I wonder how high it has to achieve steady temperature due to thermal inertia of filaments. PWM dimming would end up much cheaper than LED drivers, I was afraid that it could affect the filaments life length, but now that I know that the idea is well tested... I'll still think about a way to change the brightness without directly PWMing the filaments, but it is really tempting.
I'll definitely use direct driving, for same reasons as you mentioned - ability to use any old phone charger as power supply, to keep things cheaper and more portable. By the way - I stumbled upon this graph taken from DA-2300 datasheet: Taken from this site: http://www.dos4ever.com/numitron/numitron.html Note the logarithmic scale on tube life! W dniu piątek, 23 lutego 2018 15:10:24 UTC+1 użytkownik Mark Moulding napisał: > > I've built quite a few Numitron-based clocks, as well as other displays > using the technology. Personally, I love them: they're easy to drive, last > a *long* time, and are, to my eyes anyway, very attractive. They provide a > wonderful glow, and because they're broad-spectrum, they can be filtered to > any color. However I usually leave them "naked", and the non-monochromatic > light they emit seems to give a richer, warmer look than LEDs, or even > Nixies, to some extent. (Of course, they don't have the fully-formed > character set of the Nixies.) > > I've used a variety of schemes to power the devices. At first, I used a > dedicated microprocessor (an AT89C2051 - about $1 each) for each tube, with > the segments direct-driven from the processor outputs. I implemented a > serial communication scheme that allowed the displays to be daisy-chained > to any length, and controlled with a single 2400-baud serial signal. These > were driven using the RCA-recommended strategy of keeping the filaments > just below a visible glow whenever they were "off" for maximum lifespan, I > did this using PWM, and implemented brightness controls also, since I > already had the code to do the PWM. These worked very well, and the only > failure I've had, even in extremely rough service (a mutant vehicle roaming > the desert at Burning Man) was due to mechanical damage to the tube. > (Amazingly, it even kept working for a few minutes without any glass > envelope at all!) > > A scheme that I've never used, but which is easy and should work well, is > to use a single fixed resistor from each segment to the supply (or ground, > of course, depending upon your circuit topology) to provide the keep-warm > current for the filaments > > For most of my clocks, I've just ignored the keep-warm function, and have > seen no ill effects as a result. I've been using 74HCT595 serial-in > parallel-out latching shift registers to direct-drive the tubes; their > outputs are rated to sink 35 mA (74LS595 are even higher, at 130mA), and I > PWM the enable input to provide dimming. I've had clocks running for a > decade now with no tube or other part failures (except for wall-wart power > supplies - they're often notoriously poor in quality). The highest stress > is probably on the colon lamps, which are two 3.5-volt grain-of-wheat bulbs > that I'm running in series to match the luminosity of the Numitrons; even > though they've been blinking on and off every second for years, I haven't > had any failures there either. Note that since my clocks are often placed > in bedrooms, they're usually run at less than full brightness - PWM ratio > of around 50% or so; however, even the one I gave to my 94-year-old mother, > which runs at full power, has also had no failures. > > A note about using the Numitron clocks (or Nixies, for that matter) in > bedrooms: they're excellent for this application! A reasonable amount of > research shows that ambient light containing a significant blue-spectrum > component can disturb sleep, reducing the amount of REM sleep and overall > sleep time. This is true even when the eyes are closed! The warm glow of > Numitrons, especially when dimmed, contains almost no blue light, and so is > the ideal bedroom clock display. I'm lucky enough to have acquired most of > the remaining supply of DTF104B tubes (1" digit height, end-view), and > clocks made with these can be seen easily across a room, even if the viewer > normally wears glasses. > > I always use direct-drive in my designs, because multiplexing pretty much > obviates the big advantage of Numitrons, which is the ability to drive them > directly from the +5-volt logic supply - there isn't sufficient brightness > without a higher-voltage supply. I did use multiplexing once, to retrofit > an existing 3-digit LED display on a musical keyboard I rebuilt into a > steampunk enclosure. In this case, I simply replaced the LEDs outright > with the Numitrons, and removed the current-limiting resistors. This > actually worked better than I thought it would; although the displays were > a bit on the dim side, they were still completely legible in normal room > lighting. > > Other comments about the lifespan of Numitrons are very accurate - at > reduced voltages, the tubes will last basically forever. RCA data sheets > show a mean life expectancy at full voltage of 100,000 hours (longer than > LEDs are specified for!), and their lifespan curves are basically > asymptotic to infinity at 70% voltage. Also of note is the specified > ruggedness of these devices: rated impact acceleration (while operating!) > of 200G, vibration 5-200 Hz 20G, etc. The Russian tubes are not specified > as highly (15,000 hrs operational life - I have no idea about vibration), > but I use them all the time, and again have never had a failure. > ~~ > Mark Moulding > > > > On Wednesday, February 21, 2018 at 5:26:39 AM UTC-8, Tomasz Kowalczyk > wrote: >> >> Hi, >> I'm recently getting more and more interested in making an IV-16 clock. >> I'm planning to make 6 tubes one, so burning filament can be an issue - >> while the datasheets can state 5000+hrs, I'd like to be extra careful. >> One idea is to use a LED driver with programmable current, for >> example STP16CP05XTTR - current is set by an external resistor, so it would >> be possible to introduce dimming the display without PWM. There are >> numerous chips which allow current sinking, however I am concerned with >> power dissipation on these - that's why my choice is a package with thermal >> pad. As far as I know, most critical moment in incandescent bulbs is turn >> on due to inrush current - with a CCS this problem would simply not exist. >> However I've noticed a small mention of numitron driving in this CD4511 >> datasheet: >> https://www.ti.com/lit/ds/symlink/cd4511b.pdf >> <https://www.google.com/url?q=https%3A%2F%2Fwww.ti.com%2Flit%2Fds%2Fsymlink%2Fcd4511b.pdf&sa=D&sntz=1&usg=AFQjCNFkxbN5R5Smzeurxtf3m7gNcRqeOA> >> On last page there is a small schematic. It shows another method of >> dealing with inrush current - all filaments are prebiased with small >> current, which causes them to be already on edge of glowing - kind of how >> VFD filaments are biased. >> >> What are your experiences with numitrons? What methods of prolonging >> their life did you use? Or did you just ignore the problem, as IV-9 and >> IV-16s are still quite cheap? >> Please share your experiences and thoughts. >> > -- 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+unsubscr...@googlegroups.com. To post to this group, send an email to neonixie-l@googlegroups.com. To view this discussion on the web, visit https://groups.google.com/d/msgid/neonixie-l/eb4f6f40-8f9d-4292-83d3-45bacd3fc751%40googlegroups.com. For more options, visit https://groups.google.com/d/optout.
