Specifications

CONSTRUCTION
and 13) of
CD4066
, as
shown in
Fig. 3, is
made high,
it can switch
AC and/or
DC signals
between its
correspond-
ing output
pins (3-4, 8-
9, 10-11, and
1-2 respec-
tively) in
both direc-
tions. In other words, it acts like an ana-
logue switch which can be turned on or
off by making its input control pin high
or low. A single IC contains four such
switches/sections (A, B, C, and D). The
control inputs of the two IC
S (CD4066)
are derived from the decade counter IC
(HEF4017). Only four outputs of this IC
(Q0 through Q3) are used and the fifth
output Q4 (pin 10) is connected to the
reset pin (pin 15) via diode D1.
When power is turned on, the output
Q0 (pin 3) of this
IC
will be high. In this
condition any audio signal fed to the ‘ra-
dio I
/P terminal reaches the output. If
desired, the audio output from a radio
receiver can be connected
to this input terminal.
Circuit diagram and de-
tails of such radio receiv-
ers have appeared in ear-
lier issues of EFY.
With each depression
of switch S1, the outputs
of IC4 (Q0-Q3) go high se-
quentially to control dif-
ferent modes of operation.
When Q1 (pin 2) of IC4
goes high, the audio sig-
nals from the output of the preamplifier
reach the output terminals of the circuit.
At the same time, a 9V regulated power
supply to the preamplifier is switched on
through transistor T1. When Q2 (pin 4)
goes high, any audio signals applied to
the auxiliary I
/P terminals (Aux. I/P (L)
and Aux. I/P(R)) reach the output termi-
nals. When Q3 (pin 7) goes high, the
power to both the FM transmitter and
preamplifier is switched on and the sig-
nals from the preamplifier appear at the
base of transistor T3 (BF494) which, in
association with some passive compo-
nents, forms an FM transmitter. The de-
tails of coil L1 are included in the parts
list. The frequency of this transmitter falls
between 88 and 108 MHz.
The frequency can be slightly varied
by adjusting trimmer capacitor VC1. The
transmitted signals can be received on any
FM receiver working in 88-108 MHz
range. LEDs D2 through D5 are bilateral
LEDS which are used to display the se-
lected function.
Section II. This section employs a
JFET dual operational amplifier LF353
whose gain for different audio frequen-
cies is controlled by the corresponding po-
tentiometer settings (VR3 and
VR6 for bass, VR4 and VR5 for
treble for left and right channels
respectively) and, additionally,
by sound mode selector switch
S2. The simplified circuit dia-
gram for left channel is shown
in Fig. 4, while the complete
schematic circuit diagram is
shown in Fig. 5.
In the simplified diagram,
the function of decade counter
IC
(HEF 4017) and bipolar ana-
logue switcher ICs (CD4066) are
replaced by a simple switch, SW.
The output of preamplifier (sec-
tion I) is applied as input to the
inverting terminal of op-amp IC8
and at the output we obtain a
180
o
phase shifted amplified sig-
nal. Potentiometers VR3 and
VR4 are used to control low fre-
quencies (bass) and high fre-
quencies (treble) respectively.
In the normal mode (Q0 out-
put of IC7 high), pole-P of switch
SW is in contact with terminals
1 and 2 simultaneously. In this
condition, normal gain is
achieved for both high and low
frequencies as per settings of
Fig. 3: Internal schematic
diagram of CD4066
switcher IC
Fig. 4: Simplified schematic diagram of tone and sound
mode control (left channel)
Fig. 5: Tone and sound mode control (Section II)
31