Hein (fub) wrote,

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Nixie woes

The problem with the nixie clock as it is right now, is that more than one number will light up. Apparently this is called 'ghosting', and it is caused by the transistors 'leaking' a voltage. This is, apparently, most common with the IN-14 nixies.

The solution is simple: a set of 30 diodes and two additional resistors will do the trick: that will pull each cathode up to half of the supply voltage (in this case, 170V / 2 = 85V), which is far below the voltage needed to light up the number (in this case, 140V).
The problem with this solution is that we have already soldered everything on the PCBs we manufactured. I can either declare those two boards a loss (and try to salvage the nixies) and start over, or I could try to 'retro-fit' the diodes in there by simply drilling through the epoxy and using wire or solder to connect it all...

I am also seriously considering re-doing the whole schematic and firmware. Right now, I use direct-drive (each nixie is driven continuously), but I am considering switching over to a multiplexed design. Four nixies can be multiplexed without much difficulty, and it would mean a tremendous reduction of parts on the controller board -- which means that board can be made smaller and cheaper, certainly a factor when it comes to selling the stuff. I could even use a PIC to drive a switching mode power supply (as seen here), further saving on parts and board space...
I have some 4-to-16 decoder ICs, but those are pretty hefty (24 pins), and I wouldn't even use all of the outputs. There are also 3-to-8 decoders, but those don't have enough leads. And then there are, of course, shift registers...

First I need to finish that damned MP3 player (an awful lot of work for something that will be used only one night!), then the LED matrix for kees_s, and then we'll see what happens next...
Tags: electronics project, nixie

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