Pandicon ZM1200 in Action!

[SWISSNIXIE - Jonathan F.]

Hi folks,

Sadly, i have very little time for my hobbies at the moment because of work, but this weekend i found some time to get to my lab. While looking for a part, i digged up an old started project, laying there almost 2years. It was my attempt to build a pandicon "clock-like" device. So i looked over the schematics and parts, and soldered the last parts to actually make it work. After doing a basic electrical test, a quick arduino code brought the tube finally to life!

For driving the pandicon, i used a a few HV513 ICs along with diodes and zener diodes, inspired by the original circuit from Valvo, which can be found here:http://www.tube-tester.com/sites/nixie/dat_arch/ZM1200_valvo.pdf

Find attached my schematic if you are curious :)

Since this tube is not something everyone sees everyday, especially in a working condition, i thought id share a short video where i did some tests with the tube. There is still a bit of flickering and not code bugs, but I'm working on that

The video shows:

• Displaying a 6 digit clock, using comma and quote as " : "
• Displaying the current date with current time
• Fill the screen with random changing numbers
• "Ping-Pong" or "KnightRider" with digits

https://www.youtube.com/watch?v=1iZ8MGqne_w&feature=youtu.be

[Dekatron42]

Nice!

Have you made any tests to remove/reduce the ghosting between the digits?

/Martin

[Terry S]

Love the Pandicon.... If anyone has one for sale, PM me.

Terry

[Nick]

ZM1200s (14 digits, 10mm) are pretty rare - I have only one.

ZM1206s (8 digits, 10mm) are more common - I've seen more of those - still scarce though

IV-18 and IV-21 are still options though they are VFD not nixie.

Nick

[SWISSNIXIE - Jonathan F.]

I did tests to remove ghosting, but none seem to work

Basically i do create a timer element (50us-500us selectable)

TimerEvent 1 :   select cathode X

TimerEvent 2:    turn Anode Y off

TimerEvent 3:    wait

TimerEvent 4:    wait

TimerEvent 5:    wait

TimerEvent 6:    turn Anode Y off, reset TimerEvents

I  did this because i thought it actually would help if the cathode stays on for a while to "discharge" but it doesnt change a thing, also chaning the timer duration does not change anything, i also tried to "drive it hard" which means

TimerEvent1:  select cathode x, turn on anode Y

----

TimerEvent6:  turn both off, reset

Maybe it is an electrical issue.... will investigate further

[Paul Andrews]

Pull Anodes to ground with a 100K resistor so it drops to zero fast. Pull cathodes up to at least +75V via a 330K resistor - so they come off zero fast. 75V-90V is a good off-state for cathodes. I'll take a look at my timings too.

[Paul Andrews]

I should add: This is not for a ZM1200, just a bunch of multiplexed IN12s.

[Paul Andrews]

And I see the HV513 does the last part for you. What do you have VPP set to and how fast does it push the cathodes up to VPP?

[SWISSNIXIE - Jonathan F.]

VPP of the Anode HV513's is set to around 186V currently,

VPP of the Cathode HV513's is depending on the HV, but is around 75V, which is in spec of the 70-100V Vkk from the Datasheet

Anode OFF-Voltage is 104V which is in spec of 85-115V

If i set cathode and anode at the same cycle, the time for anode rise and cathode fall is around 2.5-5uS, same goes for deselecting

See attached two screenshots from a oscilloscope, yellow= anode, green=cathode, blue= Output Enable

[SWISSNIXIE - Jonathan F.]

Since i'm not getting any kind of positive effect by software changes (time, pattern etc),i looked at the circuit and found a small problem (V-Screen was connected to Vbias) which was fixed, sadly this changed also nothing to the problem, so i searched my old pandicon calculator in the lab and took measures.

The first very odd thing i noticed is that they don't bias the anode! They just apply high voltage on the and then go straight back to 0V at the anode. The next very strange thing is that the driver of that calculator doesn't seem to be "on" all the time, it looks like the HV turns on for a short time, and then decays to 0V "slowly". In the first screen of the scope here you can see a few anode pulses that turn on quickly and then decay to 0V, the duration of this pulse is around 2ms. In the second pic you can see one pulse magnified in time were its visible that the "steady" HV is only active for around 200uS before starting to fall

I also checked what the cathode drivers do, which turned to be exactly what i thought, the ARE biased with around 75V as specified in the datasheet and are pulled low and then return to bias. In the Screenshot you can see cathode "0 digit" (green) following anode 1 (blue) and cathode "1 digit" (yellow) following anode 2 (red). For the test i set "10" on the calculator which meant 2 cathodes have a value to display, and 6 have not! Its very interesting how the "processor" works with that. If you look at the yellow trace, which is the second cathode (which display the 1 of 10), it does not return to bias after the anode turns off, it just stays LOW for the rest of the switching cycle. Thereby the processor saves some operation to not go back to HIGH again. Very insteresting to see what kind of logic they already had at that time.

My conclusion now is that maybe i can try to not even turn anodes on that don't have to display anything, just leave it off. Currently i'm turning them on, but don't activate any cathode since i've have nothing to display. Could it be possible that a "charge" is trapped in the tube by that?

I also will make a experiment with no Anode bias, as in the calculator

If anyone here knows more about panidcons and there use i'm happy to hear about!

- Jonathan