Nixies: stupid questions.

[cowjam]

I googled for it.  Not sure I had a datasheet for my actual nixies, but I got the datasheet for the chips (which came with the nixies) by googling, and this is it: http://cowjam.co.uk/arct/k155id1.pdf

I've got some IN-35s which are just neon bulbs and they run fine at 180v (or whatever my circuit is running at) and ran fine with or without a 33k ohm resistor.
These ones: http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&item=390206146006&ssPageName=STRK:MEWNX:IT#ht_864wt_905

[FEDERICO]

We bought nixies from the same vendor :-)
Mine are those
http://cgi.ebay.it/ws/eBayISAPI.dll?ViewItem&item=400174245756&ssPageName=STRK:MEWNX:IT
I am going to try to drive them at 170v and see...
After reading about your experience I was thinking that multiplexing and optocouplers should be the safest way...

[cowjam]

Yeah, optocouplers are the way to go! 

If I figure out what happened I'll report back on here.

[wyager]

BTW guys, small neon bulbs should have at least 100K resistors (some use 200K) at 170+V or else they could burn out themselves or your circuit. I am able to multiplex them at 170v with a 100K resistor. Remember that the gas inside them will change its resistance until the voltage across the lamp is the sustaining voltage. A 200K resistor (which is probably better for long life) makes them look a little sputtery.

My A1As regulate themselves at 60V, which means that 110V gets dropped over the anode resistor. 110V/100000?=1.1mA. Almost twice the recommended amount, but I figure since I'm multiplexing... Still probably not healthy.

[FEDERICO]

wyager, thanks a lot for the advice. I am going to follow it!

[cowjam]

wyager, thanks a lot for the advice. I am going to follow it!

This ^ !

[wyager]

No problem. Also, 666 posts cowjam. 

[FEDERICO]

the number of the beast  ]

By the way i see that you (wyager) use a lot of transistors for driving your project. Don't you have a 74141 off hand?

ps. the optocouples i need, TLP627, are damn expensive 

[wyager]

the number of the beast  ]

By the way i see that you (wyager) use a lot of transistors for driving your project. Don't you have a 74141 off hand?

ps. the optocouples i need, TLP627, are damn expensive 

I was basing my project off parts I could get from digikey and I couldn't find any HV nixie drivers. The MPSA42s were only like 5 bucks for 25 IIRC, so I just went with those. I suppose after the shift registers and resistors and perfboard, the 74141s off ebay would have been cheaper, but it was a learning experience anyway. 

BTW, are the optocouples to protect the rest of the circuit from high voltage?

[cowjam]

I don't know if this will have contributed to the burnout, but I have discovered that I'd got the pins all muddled.

The power and ground pins were fine, but I had misinterpreted the position of the nixie pins so that I had the number sequence reversed.

I had also failed to spot the utterly confusing layout of the logic pins on the IC.  If you look you'll see that the pins are labelled A, D, B, C (in that order).  The logic chart is labelled D, C, B, A. 

I will have undoubtedly sent things to the IC that it wasn't expecting, though the logic chart says that should merely have resulted in no output.

[FEDERICO]

BTW, are the optocouples to protect the rest of the circuit from high voltage?

I need them for multiplexing the nixies. If I connect all the cathodes to the nixie driver IC then I need a way to switch on the 170v anodes. I am experimenting the tlc5940 but I can't let it manage the high voltage. That's way I tought about optocouplers connected to the high voltage anche my TLC to open and close the gate.

I had also failed to spot the utterly confusing layout of the logic pins on the IC.  If you look you'll see that the pins are labelled A, D, B, C (in that order).  The logic chart is labelled D, C, B, A. 

So the datasheed is wrong?? Anyway it looks like a strange way for burning an IC...

[cowjam]

No, the datasheet is fine. I hadn't read it properly.

[cowjam]

Another question: Ground sharing.

Do I share the ground for the 180v and 5v circuits?

[FEDERICO]

Just in time, I was going to ask the same question. I think that no, for what I can understand for driving for example the neon bulbs you have to ground them to the arduino with the high voltage mpsa42 transistor, right?

[cowjam]

I hope someone answers soon, I'm about to run another set up (using a shift register) and I don't to kill anything else.

Thing is, the 74141 has one ground pin and runs 5v and high volt so that must share a ground, right?