Specifications

CIRCUIT IDEAS
PENDULUM DISPLAY
CIRCUIT IDEAS
T
he circuit presented here can be
used for producing eye-catching
effects like ‘pendulum’ and ‘dash-
ing light’. To and fro motion of
a pendulum can be simulated
by arranging ten bulbs in a
curved fashion and lighting
them up sequentially, first in
one direction and then in the
other, using this circuit. For
pendulum effect, the frequency
of oscillator should be quite low.
Similarly, one may create
a dashing light effect by using
19 bulbs and connecting them
in such a way that bulb num-
ber 1 and 19, 2 and 18, 3 and
17, so on are in parallel. For
achieving the dashing light ef-
fect, the oscillator frequency
should be comparatively high.
In this circuit NOR gates
N1 and N2 form an oscillator
whose period can be adjusted
through potmeter VR1. Oscil-
lator output is fed to clock pin
15 of IC2 (CD4029), which is
a binary/BCD up/down
counter. As long as pin 10 of
IC2 is at logic 1, it counts up;
when it changes to logic 0, it
counts down. This changeover is ex-
plained below.
K.P. VISWANATHAN
RUPANJANA
The BCD outputs of IC2 are con-
nected to IC3 (CD4028), which is a 1-of-
10 decoder. As per sequential BCD in-
puts (up or down), outputs of IC3 go
high and trigger the triacs (Triac1
through Triac10) via corresponding tran-
sistors (T1 through T10) to light up the
bulbs connected to them.
Initially, when output O0 of IC3 goes
high, the output of flip-flop formed by
NOR gates N3 and N4 goes high, thus
keeping pin 10 of IC2 at logic 1, and the
counter counts up. Subsequently, when
output O9 become high, the flip-flop is
toggled and pin 10 of IC2 is pulled to
logic 0, and the counter starts counting
down. The cycle repeats endlessly.
AUDIO LEVEL INDICATOR
S.C. DWIVEDI
LOKESH KUMATH
T
he audio level indicator described
here is quite simple and utilises
readily available ICs. The func-
tion of the circuit can be understood
with reference to Fig. 2 which shows
two concentric circles formed by red and
green LEDs respectively.
When the audio level increases, the
speed of the roulette (moving light ef-
fect in the circles) also increases. The
lighting LEDs of one of the two circles
would appear to move in clockwise di-
rection, while the other circles LEDs
appear to move in anticlockwise direc-
tion. When no audio is available, the
speed of these two roulettes appears to
be constant.
Although the LEDs here are ar-
ranged in circular form and only two
colours are used, a number of different
combinations are possible. For example,
one may have red and green LEDs ar-
ranged in two rows, one over the other.
LEDs of one row may be made to ap-
pear moving from left to right and of
the other in the opposite direction, i.e
from right to left.
In the circuit shown in Fig. 1, IC
555 is wired to operate in an astable
mode as a voltage controlled oscillator
(VCO). The only difference here is that
pin 5 (which is a frequency controlling
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