Specifications

CIRCUIT IDEAS
pin connected to the invert-
ing terminal of a compara-
tor inside the IC) is not
grounded via a capacitor,
but the potential at this pin
is made to change in ac-
cordance with the audio
level. This causes the in-
ternal flip-flop of timer
NE555 to set and reset ac-
cording to the audio level,
and hence the output fre-
quency varies correspond-
ingly. This output is fed to
the clock input pin of ring
counter IC CD4017 whose
output advances at a rate
proportional to the clock in-
put or the audio level
present at pin 5 of IC2.
The audio output is not
taken directly from the out-
put of the deck (across
speaker terminals) because
the output across speaker
terminals depends upon the
setting of the volume con-
trol and would vary from
one model to the other.
Here, the left and the right
outputs (in case of a stereo
deck) are fed to the input
of an audio amplifier IC
TBA810, via capacitors C1
and C2 (0.01µF). These low-
value capacitors help to
maintain the required sepa-
ration between left and
right channels. Otherwise,
at high frequencies the
separation may fall tremen-
dously, thereby short-cir-
cuiting L and R channels.
The 10k preset VR1 be-
fore IC TBA810 is used to
control the output level so
that at maximum output
the potential at pin 5 of
555 is such that the fre-
quency of 555 is between 1
and 15 Hz (approximately). Otherwise,
all the LEDs at the output of IC3 will
appear flickering.
The other 10k preset VR2 is used to
set the normal speed of the roulette,
between 2 and 3 Hz.
One point to be noted here is, that
the audio signals should be taken from
the output of preamplifier IC of the deck
just before the volume control. The out-
put will depend on the setting of vol-
ume control (which we do not want) if
the taken after the volume control.
The power supply for the circuit may
be tapped from the power supply of the
deck, as shown in Fig. 1. The power
supply voltage in a deck is not exactly
12V DC, but is around 15 to18V. It is
preferable to connect a 7812 regulator
IC for 12V regulation.
Fig. 1
Fig. 2
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