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Registered Member #1956
Joined: Wed Feb 04 2009, 01:22PM
Location: Jersey City
Posts: 172
Hello all
I am working on a nixie multimeter for my bench. Already have a nice PSU for it. Need advice for the 'driving the tubes' part of the project. I dont like the idea of multiplexing my IN12s, I rather prefer direct driving each one of the digits. Will be 60 of them!
All the projects I found make use of the MPSA42 or very old ic's like the 74141 or similar. I dont like both!
I found this Supertec HV5522 32 channel serial-to-parallel converter with open drain outputs, capable of sinking up to 100 mA @ 200 V for each output, limited at 1,5 A for all outputs together.
I can only think this ic is suitable for driving nixie tubes. Am I missing something?
Registered Member #1334
Joined: Tue Feb 19 2008, 04:37PM
Location: Nr. London, UK
Posts: 615
The Supertex devices are already used by many nixie enthusiasts - just look at the Google NEONIXIE-L group. There are dozens of designs out there.
Main problem with the Supertex parts is simply getting them - the company doesn't like to issue samples and most of the main stockists that people use also don't stock them .
For a cathode driver, you only need to have about 80V and 5mA capacity for these tubes - Anode drivers are on the 180/200V HT+ rail, but the cathode drivers rarely see more than 50V because of the tube's own drop, even when lit. The IN12 strikes at about 170 and maintains at around 120, so with a 180VDC HT line you are only going to see 60V at the cathodes. They also only need 2mA per cathode when lit.
i.e. the Supertex drivers are huge overkill - nice in that there are less parts, but no real technical advantage. Use of discrete drivers, e.g. MPSA42s, is simple and very cheap, especially if you are multiplexing (in which case you'll need some MPSA92s or MPSA94s as anode drivers.
Remember, multiplexing is not a sin! Most of these tubes were explicitly designed to be multiplexed. Direct drive is fine, but you get more complex boards and need many more driving lines. For a 6 digit multimeter, you would use a 3*2 or a 2*3 scheme which would mean 1/2 or 1/3 as many cathode drivers as the direct drive scheme.
Another one you might consider is the HV5812 with 20 outputs - you can use 10 of them to drive cathodes and he other 10 to drives anode switches for multiplexing and the decimal point neons - have a look at Pete Hands FLW design ("Four Letter Word" design). Many other examples out there...
Do a Google search with the keywords "Supertex nixie" - over 2000 hits - Lots of possibilities.
Registered Member #1956
Joined: Wed Feb 04 2009, 01:22PM
Location: Jersey City
Posts: 172
@Nicko Thanks for the info! Multiplex makes everything easier. But I read people saying it increases tube life while other said it decreases it for older tubes.
@Conundrum I was thinking about getting a board from batchpcb. SMD is not a big deal to solder if you have a nice soldermask. If you got the PLCC it's even better:
PM me if you want to work with me on this. I want to have a first layout on the following weeks, as soon as I decide the way to go driving this valves
Registered Member #1334
Joined: Tue Feb 19 2008, 04:37PM
Location: Nr. London, UK
Posts: 615
tobias wrote ...
@Nicko Thanks for the info! Multiplex makes everything easier. But I read people saying it increases tube life while other said it decreases it for older tubes.
Most tubes, including the Russian ones, except the very earliest, were explicitly designed to be multiplexed. In 20 years of building stuff with nixies (I have several 100 different types), I've yet to find (or hear of) any evidence that multiplexing in anyway affects the life of a tube. I'm also pretty sure that no-one amongst the 400+ neonixie-l members (many of whom are professional engineers) has seen this, but it may well be worth asking just in case.
I wouldn't multiplex any of the very earliest tubes because they were never designed for it, e.g. the NU GI-10 Inditron (which doesn't even have an explicit anode) but with the later tubes its definitely not a problem.
Registered Member #1956
Joined: Wed Feb 04 2009, 01:22PM
Location: Jersey City
Posts: 172
Finish soldering everything today. While soldering I tested each one of the components. Atmega already reads the RTC time and temperature. HV5522 already shifts. "Just" missing the software now.
The BLANK input of the HV5522 is connected to an output of the uC so I can control the brightness.
On the back I have both SPI and I2C connectors, two analogue inputs and four digital inputs. The idea is to add multimeter capabilities to this as soon as the easier clock function is implemented.
Registered Member #3271
Joined: Mon Oct 04 2010, 02:29AM
Location: Canada
Posts: 159
tobias wrote ...
Hello all
I am working on a nixie multimeter for my bench. Already have a nice PSU for it. Need advice for the 'driving the tubes' part of the project. I dont like the idea of multiplexing my IN12s, I rather prefer direct driving each one of the digits. Will be 60 of them!
All the projects I found make use of the MPSA42 or very old ic's like the 74141 or similar. I dont like both!
I found this Supertec HV5522 32 channel serial-to-parallel converter with open drain outputs, capable of sinking up to 100 mA @ 200 V for each output, limited at 1,5 A for all outputs together.
I can only think this ic is suitable for driving nixie tubes. Am I missing something?
I used DS8880 high voltage drivers from National Semi. Seems to be just fine.
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Advice needed- HV5522 driving nixies
