Thank you all for your input. Currently (!) I am looking at a small A/C driver - one per display - I should be able to report back once tests have been performed - waiting on board fabrication - I would also only have the whole thing 'on' once triggered (that includes both filament and segment supplies) so most of the time - the device will be 'cold'.
As for the segments - the plan is to use a 74595 coupled to a TD62783 for switching the 24V - each tube will attach to an individual PCB - the PCB's can then be chained together - 6 planned for this clock plus a couple of colons using IV-26's (multiple dot action is planned). - Richard On Wednesday, 14 September 2022 at 16:26:23 UTC+1 gregebert wrote: > 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 [email protected]. To view this discussion on the web, visit https://groups.google.com/d/msgid/neonixie-l/d55208d8-ef7e-4491-912f-4f63a2cff1f9n%40googlegroups.com.
