Specifications

CIRCUIT IDEAS
of the feedback from Q0 to D0, point
‘A’ remains high even after releasing
the ‘off’ switch. As a result, relay
RL1 is deactivated and LED1 also goes
off.
In case of emergency, press the
emergency off switch S17 to disable all
the outputs of IC1. In this state, the
outputs of IC1 are in high impedance
state, and as all transistor bases are
almost ‘open’, all the relays get deacti-
vated.
If all the channels are to be switched
on simultaneously, a ‘low’ logic level
is applied via diodes D17 through
D24, to data inputs D0 to D7, by
pressing switch S18 to activate all the
relays.
M
any electronic devices depend
upon the shape of the signals.
It is very easy to produce
squarewave signals from sine wave,
but reproducing sinewave signals from
the square wave is quite difficult. In
case of static squarewave-to-sinewave
converter, in low frequency range, we
can get accurate sine wave, but in high
frequency range the shape will not be a
true sine wave. Here is a solution to
that problem.
The circuit shown here uses five
ICs. The squarewave signal is fed at
pin 1 of IC1 (CD 4024). IC1 is a 7-bit
counter, but here only 6 bits are made
use of. The first four bits are fed as a
signal bus to IC3 (CD4066) quad bilat-
eral switch through IC2 (CD4077B) that
contains four exclusive NOR gates. It
converts the 4-bit signal bus to ‘up
mode’ and ‘down mode’ hexadecimal sig-
nals, simultaneously. The converted sig-
nal bus switches on and off the ladder
switches inside CD4066. As a result,
the net resistance of lad-
der varies. This varying re-
sistance varies the charg-
ing and discharging cur-
rent of capacitor C1 in the
feedback path of IC5
(LM741).
The charging and dis-
charging mode is controlled
by IC4 (CD4011). In fact,
capacitor C1 works as an
integrator. The sinewave
producing circuit needs 64-
bit squarewave pulse for
360
o
sine wave. A missing
pulse in this 64-bit se-
quence produces ramp.
In this circuit, all ICs
except IC5 are CMOS ICs
and hence the current con-
sumption is very low.
The value of capacitor
C1 may be calculated from
the relationship: C1 = 0.27/
f
0
µF. The value shown in
the circuit is for 50Hz out-
put frequency. The shape
of the sinewave output
may be corrected using
presets VR1 and VR2.
(EFY Lab note. Spikes
were noticed in the output
waveform while operating
with higher frequencies in
the kilohertz range.)
J. CHOUDHURY
AN EXCLUSIVE SINEWAVE
GENERATOR
RUPANJANA
200