Automatic Dualoutput Display

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This circuit lights up ten bulbs
sequentially, first in one direction
and then in the opposite direction,
thus presenting a nice visual effect.
In this circuit, gates N1 and N2 form
an oscillator. The output of this oscillator
is used as a clock for BCD up/down counter
CD4510 (IC2).
Depending on the logic state at its
pin 10, the counter counts up or down.
During count up operation, pin 7 of IC2
outputs an active low pulse on reaching
the ninth count. Similarly, during countdown
operation, you again get a low-going
pulse at pin 7.


This terminal count output from pin
7, after inversion by gate N3, is connected
to clock pin 14 of decade counter
IC3 (CD4017) which is configured here
as a toggle flip-flop by returning its Q2
output at pin 4 to reset pin 15. Thus
output at pin 3 of IC3 goes to logic 1 and
logic 0 state alternately at each terminal
count of IC2.
Initially, pin 3 (Q0) of IC3 is high
and the counter is in count-up state. On
reaching ninth count, pin 3 of IC3 goes
low and as a result IC2 starts counting
down. When the counter reaches 0 count,
Q2 output of IC3 momentarily goes high to
reset it, thus taking pin 3 to logic 1 state,
and the cycle repeats.
The BCD outputs of IC2 are connected
to 1-of-10 decoder CD4028 (IC4).
During count-up operation of IC2, the
outputs of IC4 go logic high sequentially
from Q0 to Q9 and thus trigger the triacs
and lighting bulbs 1 through 10,
one after the other. Thereafter, during
count-down operation of IC2, the bulbs
light in the reverse order, presenting a
wonderful visual effect.