I would guess that reason to set the 'off' voltage of both the anode and the cathode to the same values is to ensure that no current flows. Not sure why they picked 80V instead of, say, 0V for that. In the scheme I suggested, the anode would be pulled to 0V while the cathodes would be up at 80V. Not ideal, but the current flow should be minimal with that voltage difference.
My own experiments did not have a means to both push and pull the anodes/cathodes, so I relied on a pull down resistor for anode and a pull up resistor for the cathodes. I bread-boarded the design extensively before committing to it. Note that it is truly difficult to breadboard a multiplexed scheme. In my experience, the finished PCB will perform more reliably. Richard, I think you can calculate the required current by multiplying the steady current by off-time/on-time. A ballpark figure would be Is * num-tubes. Then start with like half that :), but don't go above 10mA. BTW, what does the note translate to? Connection sequence? On Wednesday, May 26, 2021 at 1:08:35 AM UTC-4 gregebert wrote: > Interesting. Anodes and cathodes are biased to 80V. Also, note that the > segment drivers use current-limiting (emitter resistors). > > On Tuesday, May 25, 2021 at 8:48:50 PM UTC-7 Richard Scales wrote: > >> OK, I think I'm homing in on a solution. >> >> Assuming that I go with HV513 for high and low sides with the VPP's set >> accordingly there is then the whole series resistor thing to work out as I >> believe that peak currents can be higher in a multiplexed situation (did I >> read that right?). The circuit that I have seen for the Bally Pinball >> displays appear to be using a total of 1k5+1k2=2k7 though I have no >> knowledge of the specification of the displays that they were using. >> >> For the ZM1500 displays I have here - the specification suggests anode >> current between 0.4mA and 1.0mA with a maintaining voltage of 125V >> (assuming that I translated that correctly). >> >> Assuming a current of 0.5mA and a supply of 170V that suggests a series >> resistor of (170-125)/0.5 K = 90K, a world apart from the values that >> Bally are suggesting but I don't know their displays characteristics. >> >> Is there a suggestion that, depending on the 'on' time of the segment, >> the actual current could be set higher? >> >> The same specification also lists an anode peak current of 10mA. >> >> For now I'll plan to use something like 90K on each cathode to see how >> that goes - unless anyone can suggest that is hideously wrong? >> >> - Richard >> >> [image: Bally.JPG][image: ZM1500.JPG] >> >> On Tuesday, 25 May 2021 at 20:11:18 UTC+1 Paul Andrews wrote: >> >>> The HV513 is push/pull. You can use it for the anodes and the cathodes. >>> You set Vpp to 170V for the HV513 you are using to control the anodes. You >>> set Vpp to 80V for the HV513 you are using to control the cathodes. Each >>> pin can source or sink 20mA. You could even chain them all together, as far >>> as the SPI interface is concerned. >>> >>> You could use a resistor divider for the 80V, or you could use a zener >>> voltage clamp. There should be next to no current flowing when the cathodes >>> are at 80V (otherwise they would be lit). >>> >>> On Tuesday, May 25, 2021 at 1:25:44 AM UTC-4 Richard Scales wrote: >>> >>>> I think I am getting a little closer to understanding this all a little >>>> bit more. I have almost grasped the concept of clamping the cathodes at an >>>> intermediate voltage to aid switching them on and off in a timely manner >>>> in >>>> an effort to minimise ghosting. >>>> >>>> Now it's all down to driver choice and chip count. >>>> >>>> How about HV5812's? i have seen these used in multiplexing circuits - >>>> especially those where a group of say 6 nixies are split into two groups >>>> then the 20 bits from the driver are split into two groups of 10 bits, >>>> each group for one set of three nixies. that works just fine for nixies, >>>> not so good for a 16 digit device with cathodes common to all! >>>> >>>> Regardless, it would be slightly more efficient than using a 32 bit >>>> device though ultimately an 8 bit device would suffice. Using the HV5812 I >>>> can see that I can just connect Vpp to 80V, job done. If I wanted to use >>>> HV513 (on the grounds that I only need 8 bits) would I then just clamp >>>> each >>>> cathode to 80V via a suitable resistor? >>>> >>>> I guess I could simply not worry about it and waste the bits, I'm only >>>> ever going to do this once or twice and one of my design goals is to make >>>> this thing as small as possible. >>>> >>>> For the high side i definitely need to switch 16 anodes so I need to >>>> employ a push/pull device - HV5523 will do that or I could perhaps use a >>>> couple of HV513's - again, the easiest thing to do would be to use a >>>> single >>>> HV5523 and waste half of the bits. >>>> >>>> In an effort to home in on a solution - a single HV5523 for the 16 >>>> anodes and a single HV5812 for the cathodes (clamped to 80V) - have I >>>> missed anything crucial here? >>>> >>>> I just feel that I should get a handle on this multiplexing thing. I >>>> now have a couple of different multi digit panaplex displays coming so I >>>> need to come up with a plan. >>>> >>>> I have some ZM1500 (12 digits) on hand and some IGP-17 (16 digits) on >>>> their way. >>>> >>>> ... and I've not even started to think about the timing of all the >>>> various switching operations yet! >>>> >>>> Thank you all for helping me with my education >>>> >>>> - Richard >>>> >>>> On Friday, 21 May 2021 at 19:13:35 UTC+1 nixiebunny wrote: >>>> >>>>> Richard, >>>>> A single push-pull HV driver chip will not be able to drive a >>>>> multiplexed display. >>>>> >>>>> The reason is that it only connects each tube element to either 0V or >>>>> 180V. It is not capable of leaving an element disconnected. >>>>> >>>>> >>>>> On Thu, May 20, 2021, 8:45 PM Richard Scales <[email protected]> >>>>> wrote: >>>>> >>>>>> Sorry, I mean using the same type of device to control the anodes AND >>>>>> the cathodes but but the actual same piece. >>>>>> So, using an HV5523 (or perhaps multiple HV513, multiple because >>>>>> there are probably 8 cathodes (seven segment panaplex displays) and 16 >>>>>> Anodes (16 digits)) could be a way forward then. >>>>>> Please could you let me know more about the need to clamp the >>>>>> cathodes to a certain voltage? (Exposing my real lack of understanding >>>>>> here!) >>>>>> - Richard >>>>>> >>>>>> >>>>>> -- 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/572b8c59-860e-41b7-a271-5e19cf317cbbn%40googlegroups.com.
