On my boards the cathodes for each segment are wired together and presented at the edge of the board. The grid is permanently connected to HV via a large value resistor. So each segment is like a cathode in a regular nixie tube - pull it to ground and it turns on, let it float and it turns off.
With the boards that Richard has, all the cathodes on the board are connected to ground via a resistor. All the anodes are connected together. It is the grids that are grouped together and presented at the edge of the board. With IN-28s you pull the grid controls whether a tube will light up or not when the cathode is pulled to ground. If you want a tube to light up, you have to pull the grid high. Once it is on, you can let the grid float - not sure if it also stays lit if the grid is pulled to 0V. So in practice what you do is this: 1. Turn all the tubes off 2. Let the grids float for those segments that should stay off, pull the others high (e.g. up to the anode voltage) for those segments that should be on. Note that in Richard's case, his boards have a pullup resistor on the grids, so you have to actively pull them down for those segments that you want to stay off and let them 'float' for those that should turn on. 3. Turn all the tubes on - the segments with a high grid should light up With pulsed DC (un-smoothed rectified AC), all the tubes turn off at twice the mains frequency, because the voltage falls below the maintenance voltage. So you can just permanently connect the cathodes to 0V and the anodes to HV. When the voltage gets high enough, only those tubes with the grid high will turn on. So in this case, all you need to do is pull those grids low for the segments that what you want to be off. The boards effectively read this state around 120 times per second. Pretty simple. If you have steady DC, you have to turn the tubes off yourself, by letting the cathodes float before you change the state of the segments using the grids. If you do this, you will have to be able to handle between 200mA - 250mA per board with whatever is pulling all those cathodes to 0V. So you can see that using un-smoothed, rectified 240V makes this a lot easier. As for what you can use to pull those grids low, I have no idea. You probably don't have to drop them all the way to 0V and I am pretty sure you don't have to let them go all the way up to the anode potential. I guess, in some ways, my boards are easier to drive because we all know how to drive nixie tubes, and my boards just look like very big 7 segment nixies. On Friday, October 16, 2020 at 9:05:19 AM UTC-4 Bill Notfaded wrote: > Anyone have any PNP transistor recommendations? Seems like SOT-323 size > would be possibly ok if I could find some that can take enough voltage. > How high of voltage should I be thinking about for these? You have to bear > with me because I'm a CIS not an EE. For me the I2C parts make much more > sense than the analog EE parts. Would ON MSD42WT1G work or is 300V not > enough would you think? Wait they can't carry enough current can they... > ugh! > > Bill > > On Friday, October 16, 2020 at 5:43:23 AM UTC-7 Bill Notfaded wrote: > >> I found some of these power supplies now that put out 0-500VDC 0-2A with >> 4 sets of outputs. This seems perfect for a four or probably even 6 digit >> clock if the tubes are driven PWM. The power supplies even have 1V >> resolution. These power supplies have a fan in them so I'm interested to >> see how loud they are. I don't really want some loud power supply fan but >> if you think about it 500V @ 2A o.O that's some 1000 watts we're talking >> about. So say the power is good now. I'm interested now in the switching >> of the HV. I'm curious if PCA9685 could be used to PWM using some HV NPN >> transistors? What we need is a PCB design that can route all these control >> lines for all these tubes. This is a LOT more than a usual 4 digit clock >> with 0-9 cathodes to control. One thing that seems nice about the PCA9685 >> is that the phase of the PWM can be controlled so we could make it so all >> the tubes don't turn on and off at the exact same time. Has anyone played >> around with this kind of a configuration before? It would also be nice if >> the transistors could come in smaller package because geesh we need a F' >> load of these things on the PCB. The PCA9685 is 16 channel. So 6 would be >> needed because 23 x 4 = 92 tubes and 92 / 16 = 5.75. I'm kinda thinking >> out loud here so if I'm totally off on this idea someone please let me >> know? It seems like I2C control of the tubes duty cycle and phase would be >> pretty sweet for dimming right? >> >> Bill >> >> On Friday, October 16, 2020 at 3:57:34 AM UTC-7 Bill Notfaded wrote: >> >>> This is exactly correct Paul and I have both shown the 500V models we >>> have here. I bought a second 500V one. I like the fact that some have >>> four outputs too. These are used for genetic research. >>> >>> Bill >>> >>> On Thu, Oct 15, 2020, 1:20 AM Paolo Cravero <[email protected]> wrote: >>> >>>> Hi. >>>> >>>> The PS Paul and I have goes to 500V but I've found some that goto 300 >>>>>> which seems perfect for this with 4 sets of outputs! >>>>>> >>>>>> >>>>>> >>>>> >>>> Maybe it is not what Bill meant, but electrophoresis power supplies >>>> come in ranges up to 300Vdc (minimum) and few dangerously hundred mA. Add >>>> a >>>> current limiting circuit for human safety as suggested by gergebert and >>>> you're set. Easy to find in US and UK over eBay. With some patience can be >>>> had with less than 100 USD/EUR/GBP. >>>> >>>> Paolo >>>> >>>> -- >>>> You received this message because you are subscribed to a topic in the >>>> Google Groups "neonixie-l" group. >>>> To unsubscribe from this topic, visit >>>> https://groups.google.com/d/topic/neonixie-l/bVoCKhPv7Dg/unsubscribe. >>>> To unsubscribe from this group and all its topics, send an email to >>>> [email protected]. >>>> To view this discussion on the web, visit >>>> https://groups.google.com/d/msgid/neonixie-l/CABj2Vaaso61iFnB9fD80BUCD1TepGQzNeuXnD8PUG3oiuX9Kkg%40mail.gmail.com >>>> >>>> <https://groups.google.com/d/msgid/neonixie-l/CABj2Vaaso61iFnB9fD80BUCD1TepGQzNeuXnD8PUG3oiuX9Kkg%40mail.gmail.com?utm_medium=email&utm_source=footer> >>>> . >>>> >>> -- 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/031ad40d-88ac-459f-9bb9-430790ef3326n%40googlegroups.com.
