Another stepping stone you might consider (although it is completely
backwards) would be a 16-segment VFD based FLW.
I know that I personally would be very interested in such a device,
given the significantly higher VFD availability than B7971. VFD's are
common cathode and are voltage regulated rather than current regulated
as nixies&LED's are.
As for how to drive Nixies versus common anode LED's.. They're pretty
similar. Just as you say: Higher voltage & higher current. In both cases
you are sinking current through a voltage limiting resistor. Your
current limiting resistor calculations will be different, your supply
voltage will be different, very likely your driving IC (or transistors)
will be different. They easy NPN transistor that is commonly used is the
MPSA42. Other than that, there are tons of different options for driving
the nixies ranging from the antiquated 74141 to the supertex parts to
all kinds of solutions.
-Adam
On 6/6/2012 4:13 PM, Matthew wrote:
Many thanks again for the help on this. Somewhat improbably, I now
have a working LED-based prototype on the breadboard - it includes the
modes of the original and a few new ones too. I have multiplexed it
for now - to save space and bits at least - I started out the hard way
but then discovered the timer interrupt of the Arduino chip which
makes it much easier. But my display is fairly well abstracted from
the rest of the code so if it turns out I want to direct drive, it's
not rocket science to change it.
So my circuit is fairly simple - In each multiplex cycle, the Arduino
writes out to 3 74HC595 shift registers:
* 1 controls the anodes of the 14 segment displays (just one at a time
in this case) - these go through 2N3904 transistors, since the total
draw of one character is more than the register can handle
* The other two control the segments; for now I'm using resistors such
that the 74HC595 can sink the current so they are connected directly
to the cathodes.
Now thinking about moving up to the tubes. Very simplistically, I'm
seeing the eg B7971 as a bigger version of the common-anode LEDs I'm
using - just requiring a higher voltage and current, so needing to be
driven through appropriate transistors. I'm sure it can't be *that*
simple though - can anyone broadly summarise what other things I need
to consider?
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