Specifications

CIRCUIT IDEAS
quartz clocks and is readily
available in the market. But use
of a 1kHz crystal using a quad-
NAND IC CD4093 as clock gen-
erator, as shown in Fig. 2, is bet-
ter as it provides the exact time
interval required. In that case,
CD4060 oscillator/divider is not
required.
The CD4017B counter-cum-
decoder IC then divides this
1kHz signal into ten equal in-
tervals, which are programmed
via the single-pole, 10-way ro-
tary switch. Once the delayed output
reaches the desired time interval, the cor-
responding output of CD4017 inhibits the
counter CD4017 (via pole of rotary switch
and diode D6) and fires the Triac. Tran-
sistor T2 here acts as a driver transistor.
The reset pin of 4017 is connected to zero
crossing detector output to reset it at ev-
ery zero crossing. (The load-current wave-
forms for a few positions of the rotary
switch, as observed at EFY Lab, are
shown in Fig. 3.)
The circuit can be used as power con-
troller in lighting equipment, hot-air oven,
universal single-phase AC motor, heater,
etc.
S.C. DWIVEDI
W
hile travelling by a train or bus,
we generally lock our luggage
using a chain-and-lock arrange-
ment. But, still we are under tension, ap-
prehending that somebody may cut the
chain and steal our luggage. Here is a
simple circuit to alarm you when
somebody tries to cut the chain.
Transistor T1 enables supply to
the sound generator chip when the
base current starts flowing through
it. When the wire (thin enameled
copper wire of 30 to 40 SWG, used
for winding transformers) loop
around the chain is broken by some-
body, the base of transistor T1,
which was earlier tied to positive
rail, gets opened. As a result, tran-
sistor T1 gets forward biased to extend
the positive supply to the alarm circuit.
In idle mode, the power consumption of
the circuit is minimum and thus it can be
used for hundreds of travel hours.
To enable generation of different
DHURJATI SINHA
LUGGAGE SECURITY SYSTEM
Select 1 Select 2 Sound effect
(Pin6) (Pin1)
X X Police siren
V
DD
X Fire-engine siren
V
SS
X Ambulance siren
“-” V
DD
Machine-gun sound
Note: X = no connection; “-” = do not care
alarm sounds, connections to pin 1 and 6
may be made as per the table.
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