■ FIGURE 4. Six Stage Ring Counter Schematic.
base emitter junction of a transistor. Those transistors,
as well as others, are used to drive the digits of the
The schematic in Figure 3 is indicative of the divide
by 10 rings. It depicts the simpler 1-transistor trigger circuit
which is used in the first two rings which divide the 60 Hz
down to 1 Hz. Notice that the transistor is capacitively
coupled to the ring, driving the positive side towards
ground in short pulses.
The schematic in Figure 4 is indicative of the divide
by 6 rings. It depicts the more complex three-transistor
trigger circuit used in the latter five rings. This trigger
circuit uses the first two transistors to clean up the pulses
from the previous stage which then are capacitively
coupled to the third stage
which is then tied directly
to the ring. This provides a
short, clean pulse to ground
with each input transition
from low to high.
Figure 4 also depicts the
nixie tube drivers. For driving
the nixie tubes, three of the
diodes tied to ground in the
standard ring are replaced
with the base-emitter
junction of a transistor. When
the neon lamp lights, the
transistor turns on which
lights the appropriate digit.
This works for half of the
digits. To drive the other half
of the digits, a transistor is
tied to the lamp side of the
44 August 2009
■ CPU Diagram
resistor through a resistor. The transistor drivers are only
used in the ring for the minutes and the ring for the
10s of minutes.
To indicate hours, a 12 stage ring (which is not
shown) is used. This ring is similar to the divide by 10
stage adding two stages to the ring, as well as using the
three-transistor trigger circuit.
Ring Counter Operation
The ring counters work by relying on the fact that the
neon lamps require a higher voltage to turn on than to
remain lit. Figure 3 will be used to explain the operation
of the ring. On initially powering up the ring, one (maybe