@Nick - I know that cathode current control per segment might seem a bit of an overkill, but as @greg said, considering the price of the tubes, I think we should do our best to meet all of the datasheet specs if possible. And if you carefully look at the datasheet, consider the case you want to display a character like "*" (asterisk), then add together the currents of each segment from the datasheet and it will exceed the maximum anode current defined in the same datasheet, this is why each cathode current should be adjusted so that if you add them all together, the sum will be lower than the maximum anode current (of course, how much this really impacts the life of the tube will remain a mystery I guess, but we should still be careful)
This could be achieved by adjusting the resistor value in each of the segment lines but this carries a side effect. These tubes will presumably run in our clocks for years and during the that time, their characteristics will probably change. The voltage drop on the tube will probably change and if the supply voltage is fixed this will also result in changes to the segment current (Is = (Ua - Um) / Rs). If Um rises over time, this would result in lower voltage drop across the resistor and in turn lower the segment current (perhaps to the point where brightness might not be what we would like it to be) and this is why a constant current sink might come handy to make sure current in each segment remains fixed over the years of operation. Dana četvrtak, 11. svibnja 2017. u 17:36:02 UTC+2, korisnik gregebert napisao je: > > The problem is that if the segment currents stated in the Burroughs > datasheet are summed-up for various characters, many characters exceed the > max-spec for anode current. However, the average character-current is > on-par with the max anode-current spec. Unfortunately, we'll never know > what Burroughs intended. > > I took a different approach and gathered a lot of data on my 7971's, > including a guesstimate of the current that gives good visual illumination > for each segment. > When I scaled-back the spec-value for segment currents to get most > characters within the 22mA max anode-current spec, I found that the > 'visually good' current was on-par with the scaled current. What I ended up > with is segment currents that are visually good, and within the > max-anode-current spec limit (slightly over for 2 characters). > > Hopefully I will have time this weekend to finish my board and try it out. > -- 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 post to this group, send an email to [email protected]. To view this discussion on the web, visit https://groups.google.com/d/msgid/neonixie-l/a4d95431-e69e-4e94-98be-d782587d70fd%40googlegroups.com. For more options, visit https://groups.google.com/d/optout.
