Like John said, 20uS is way too short. Most nixies won't even respond. It 
can take close to 50uS for a nixie tube just to ionize. Here's an old 
scope, photo I took, of some signals going into a NL-905 nixie tube:

<https://threeneurons.files.wordpress.com/2011/08/timing01.jpg>

I stepped the anode voltage On for 4mS, then kept it Off for 12mS, and 
repeated, for a 16mS total period, or ~64Hz.


The Anode is turned On at the beginning of the trace. Notice it takes 30mS 
for the tube to even start conducting. Full conducting at ~50mS. It varies 
some with different model tubes, and quite a bit with anode voltage. I did 
some speed tests, some 10 years ago, but lost the file. I used a few types 
of nixies, and varied the anode supply from 180 to 200V. Got the best 
results with a ZM1000, at 200V, and using its primer (-100V 10M ohm) 
electrode. I got it to strike in 7mS. The presents of light also speeds up 
ionization.


When I multiplex nixies, I nominally use ~200uS interdigit "blanking". 
Blanking is when no digits are On. Nothing set in stone, about 200uS. 
That's just close to the minimum, I suggest. Any time from ~150uS to 1mS is 
good.


100Hz (10mS) total frame rate (cycle thru all digits) was mentioned. So if 
its 3 x 3, then each set of 3 digits is one for roughly 3.3mS, less the 
blanking interval. 3.3+3.3+3.3 roughly equals 10 (9.9 is close to 10 for 
our purposes). Personally, I can't see any flickering, even as slow as 40Hz 
(25mS), but I'm old. You can always vary the frame rate, and test it on 
your self. If you're not going to do anything fancy like "cross fading", 
then that 100Hz is a good figure to use.



> To load the HV5122 it takes 5us. 
> And i would leave the digits on for 15us for example.
> This would result in 20us cycles at a 50/50 duty rate.
>
> Has anybody experience with multiplexing?
>
> Is 20us too long, just right, too short? 
> I would like to see no flicker, if possible
>
>

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