Another thing to consider is when to turn filaments on and off. Having a PIR motion sensor to turn-off the segment supply is important, because long-term you will see dark regions on the phosphor closest to the filament.
Turning filaments on and off too many times will wear them out from thermal cycling. Having series resistance to reduce the peak inrush current will help a lot to extend their life. But leaving them on 24/7 might lead to wearout as well. I have the same issue with my NIMO tube clock (I expect to post more details and a video in a few weeks). NIMO tubes are basically irreplaceable, so burning-out a filament is a death sentence for the tube. For now, I have programable timers for 3 states: cold (filaments off) warm (filaments on, high voltage off) on (filaments and HV on) - Tubes are readable To go from cold-to-warm, the software requires a few seconds of PIR activity so that peeking into the room wont trigger it. Warm-to-on will happen with any PIR activity. What I dont yet know is how long I should keep the clock in the warm state. Too short, and there will be excessive filament cycling. Too long, and it leads to wearout. For now, the warm timeout is 100 seconds, and the cold timeout is 24 hours. After the novelty of this clock wears off, it will be put in standby mode where it's just keeping time and the display is disabled. On Wednesday, September 14, 2022 at 6:35:29 AM UTC-7 Paul Andrews wrote: > Arghh - I accidentally hit send on that last one. So anyway, if you don't > plan to use the grid to turn the tube off, you can wire it to the segment > positive voltage and ignore the need for a bias. You still might want to > put the series resistor in though. The exact value you use is going to > depend on the cold and hot resistance of the filament. Oh, also if it > wasn't clear from my second point, the series resistor acts as a voltage > divider, so you have to figure out what the total total voltage across that > resistor and filament should be. > > In my VFD clock I needed two different filament voltages, so I use a buck > converter to get the larger of the two and used a series resistor to > produce the lower. In retrospect it might have been better to use series > resistors for both and have a higher regulated voltage - the resistances > are all very small and it would help smooth over any variations in > individual tubes and resistors. > > So the easiest way to figure out these values is to measure the filament > resistance when cold to get an initial value for the series resistor, then > start experimenting and measuring. > > On Wednesday, September 14, 2022 at 9:25:57 AM UTC-4 Paul Andrews wrote: > >> I don't know the specs for these specific tubes, but a resistor in series >> with the filament servers a couple of purposes: >> >> 1. It reduces the inrush current (i.e. when the filaments are cold). >> The resistance of the filaments is low when they are cold, so if you put >> the steady-state voltage across them in that state, there will be a much >> greater current. For this purpose the series resistor value should be >> high >> enough to drop that current within the specified limits of the filament. >> 2. Putting a resistor between 0V and the filament raises the base >> voltage of the filament above 0V. If the tube has a grid, it is typically >> specified to be at a negative voltage with respect to the filament so >> that >> it can be guaranteed to cut off the current when pulled to that voltage. >> An >> easy way to achieve this negative bias is to raise the filament voltage >> above 0V and keep the grid at 0V. >> 3. >> >> >> On Wednesday, September 14, 2022 at 4:16:12 AM UTC-4 Richard Scales wrote: >> >>> I think I already see blunders in my original post - the filament is the >>> cathode (I think) at 5V, the segments (individual anodes) at 25V giving a >>> 19V difference over the grid which is at 5V. >>> I am unsure as to the correct value of the series resistor for the >>> heaters- 10R has been used by others though I would prefer to know how that >>> was calculated and indeed whether there are significant gains to be made by >>> moving to an A/C drive for the filaments. >>> - Richard >>> >>> On Wednesday, 14 September 2022 at 09:02:24 UTC+1 Richard Scales wrote: >>> >>>> Hello everyone, >>>> I have just managed to acquire a set of these and would ideally like to >>>> drive them the best possible way. >>>> I had initially though about a 5V for the filament and then 24V for the >>>> cathodes and grid. >>>> The clock would only have segments activated when someone is nearby - >>>> the segments will not be left on all of the time. >>>> Now I read about A/C supply to the filaments and wonder if I should be >>>> going that way. >>>> Would anyone be able to post their findings and/or suggest the right >>>> way forward? >>>> [image: VFDsnip.JPG] >>>> >>>> I just noted that the picture above shows the connection for the grid >>>> (pin 9 on H1) connected to 5V and not the 24V as used on the cathodes. >>>> The more I think about it - the less clear this all becomes! >>>> I need to get it right in my head before I go breaking something and >>>> then I would like to get the best possible result via reasonably straight >>>> forward means. >>>> Would anyone be able to point me in the right direction and/or share >>>> proven drive methods? >>>> - Richard >>>> >>>> >>>> On Monday, 16 September 2019 at 22:23:47 UTC+1 gregebert wrote: >>>> >>>>> Yes! That's exactly what happens. The current through the center-tap >>>>> is the sum of the anode (segment) current and the grid current. And the >>>>> peak current through the filament wires is actually *greater* than >>>>> just the current to heat the filaments. >>>>> >>>>> >>>>> *Tomasz* - As you found out, those VFDs draw a lot of current. I have >>>>> a future design for a 6-tube ILC1-1/8 (smaller tubes than the ILC1-1/7) >>>>> and >>>>> I'm just going to use a high-current filament transformer with the >>>>> center-tap at GND. Grids will NOT be pure DC; closer to full-wave >>>>> rectified >>>>> around 15-16V. Segment anodes will be pure DC around 36-40V with >>>>> current-regulators and non-multiplexed. >>>>> >>>>> I actually have an Op-amp summer+ADC+Software to monitor the current >>>>> thru the center-rap on my NIMO clock to determine the tube health, >>>>> though >>>>> it's orders of magnitude smaller (30uA per tube). >>>>> >>>>>> -- 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 view this discussion on the web, visit https://groups.google.com/d/msgid/neonixie-l/a740e50e-88e7-4b97-ac32-9248b36e3dc5n%40googlegroups.com.
