Cold War Era Glow Discharge Redundant Rev Counter for the Bus.
a universal nixie tachometer
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Last updated July 28, 2019.
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Sexy Russian Neon Love.
There are far simpler ways to skin this kitty with
cheap and readily available modern
programmable logic, and arguably, point to point
hand rolling a potentially less functional fancy end
result using a greater number of parts seems
somewhat .. archaic.

But this is in fact exactly what we're going to do
here.

No microcontrollers, no IDE's, no code downloads.
Like the Heath offerings of an era passed: Wire it
up correctly, adjust a trim pot or two, and it works.

Admittedly I have no "good" reason for such an
approach, Engineering, in theory, should employ
the simplest and most elegant solution to any
given problem.

"But I remember a time of chaos, ruined dreams,
this wasted land..."

There was a time when nerds of my vintage would
rush religiously to the news stand, anticipating the
arrival of the latest Gernsback periodical.

Only to discover that the featured project required
a pre-programmed PROM, a schematic too
complex to publish in it's entirety, or some other
obscure part that required sending away for.

Although to be certain the DIP parts selected for
this project are decades obsolete, they are still
not difficult to source.

This Nixie tach build, which will take place in the
evenings, after hours on my Mississauga work
bench will as well be filmed in it's entirety as a
video experiment, without editing from concept to
completed project.

At the time of this writing, I have yet to breadboard
a fully functional circuit (Although I already have a
general block layout in mind and know which
components will be utilized), or generate a
schematic diagram. The experiment will be to do
this together.
The money shot. Four new old stock planar Russian
"Nixie" tubes and sockets. These, what I happen to have
in sufficient quantity with large enough digits for easy
viewing, but virtually any tube in any style will work with
little or no adjustment to the circuit.
The meat and potatoes with 5V buses in place. An
LM2917 will do prescaling duty, an ICL-7135 and
SN-7441 will decode and display the results.

One 555 will be used for the time being to "freewheel"
drive the high voltage boost converter FET for the
anodes, the other to supply the 120KHz clock signal to
the 7135, selected do to their relative ease of use and
stability - in effect, so as not to add "wild cards" to the
circuit during the initial breadboard thrash phase.

As well, arguably a bit of a tease, the Nixie's themselves
will not be placed in circuit until the very end - instead a
handful of NE-2 lamps emulating their function.

This nothing to do with worry of damaging the tubes
during testing, they're virtually indestructible. Instead,
just to keep the breadboard uncluttered until the
working circuit is transferred and soldered permanently
to perfboard.