Hmm... I was messing around with pull-mid resistors a bit. 100K pull- mid resistors on cathodes 4 and 8 seem to mostly alleviate the problem. The only problem is, with two sets of multiplexed tubes, that's four cathodes I have to pull low, which is the equivalent of four 200K resistors in parallel, which burns 3.4 extra mA. I'll have to mess around with different resistor values, but it probably won't work as well.
Pull-mids on the anode have some effect, but I have to use resistances low enough that they also seriously dim the tube. Cathode pull-mids seem to have no effect on brightness. On Feb 9, 10:18 am, will <[email protected]> wrote: > Oops! I have to fix that schematic... Yes, my cathodes are grounded > properly (although I guess I'd better check when I get home?). I'll > take a look at your schematic and try midpull resistors some more. > > On Feb 9, 1:25 am, threeneurons <[email protected]> wrote: > > > > > > > > > On Feb 8, 9:10 pm, will <[email protected]> wrote: > > > > This is so confusing! My DMM measures literally 10mV across its > > > internal 10megohm shunt from (off) anode to ground, which means that > > > the anode is truly OFF... My DMM reports infinite resistance from > > > cathode to ground when it's set to off... Everything seems to be > > > working perfectly! > > > > As a possibly related side note, one of the tubes is slightly brighter > > > than the other, even though their sustaining voltages are within a > > > quarter of a volt of each other and their anode resistors are within > > > 500 ohms. Could this mean anything? > > >http://sites.google.com/site/willyager/nixie-clock > > > Not to ask a dumb question, but are the emitters of your cathode > > transistors grounded ? The schematic omits showing that connection. > > Since the board is hand wired, you probably have grounded them, > > indifferent to the schematic omission. If you did leave them > > unconnected, the problem would be worse. > > > I'm still thinking its one of the two issues already mentioned: (1) > > Timing and/or (2) leakage. > > > The 'midpull' resistors, mentioned, usually can address the leakage > > problem. I think they showed only connections to the cathodes, but the > > anodes should also have a resistor tied to them (100K-470K) that's > > connected to a middle voltage (80V-100V). > > > My third nixie clock uses 4 IN-14s, is multiplexed (1 of 4), by a AVR > > mega8 uC: > > >http://snipurl.com/10zg1u > > > The cathode driver is a pair of SN75468 HV darlington pairs. Part of > > one chip is used as part of the anode drive. The coupling caps are > > needed since the SN75468 can only handle 100V, but the MPSA92s are all > > the way up at ~200V. Cap coupling was (and is) and old technique to do > > level shifting. It has midpulls on both the cathode and anode side. No > > ghosting at all. Been running since 2004. -- You received this message because you are subscribed to the Google Groups "neonixie-l" group. To post to this group, send an email to [email protected]. To unsubscribe from this group, send email to [email protected]. For more options, visit this group at http://groups.google.com/group/neonixie-l?hl=en-GB.
