1. CIRCUIT
IDEAS
IVEDI
BELL-CUM LIGHT CONTROLLER S.C. DW
SURESH KUMAR K.B. the inhabitants for activating the transistors T1 and T2.
above-mentioned timer for switching IC1 is a 14-stage binary counter and
T
his bell-cum-light controller on the light for three minutes from in- oscillator IC. In its quiescent state, the
circuit is equipped with four side the house. S2 is meant to be used Q13 output (pin 3) is high, which re-
switches labelled S1 through during darkness with S4 ‘on.’ sults in conduction of transistor T1 to
S4. While S4 is the mains ‘on’/‘off’ Like S1, switch S3 (labelled ‘call- cut off transistor T2. Thus the relay is
toggle switch for powering the timer bell’) is located outside the entry gate. in de-energised state and the bulb is
circuit for lighting up a bulb for a spe- It is meant to be used during day, ‘off.’
cific duration (mainly during night), when mains switch S4 is ‘off.’ When When the master reset is activated
the functions and placement of the switch S3 is pressed, it activates only by pressing of switch S1 and/or S2,
other three switches (which are push the bell circuit for as long as the switch all the output pins of IC1 including
switches) follow. is kept pressed. Since the bell circuit is Q13 output go low. Thus transistor T1
Switch S1 (labelled ‘call-bell and powered by a 3V battery, this circuit is cut off, while T2 conducts to energise
timer-on’) is located at the outer entry can be activated even if mains switch relay RL1 as also the bulb. Once S1
gate of the house for use by a visitor. is off. and S2 are released, the timer starts
This switch activates bell circuit for as With switch S4 ‘on,’ the supply to counting.
long as the switch is kept pressed. On bulb B1 is routed via N/O contacts of Pressing of switch S1 additionally
its release, a timer is initialised, which, relay RL1. Simultaneously, the AC results in forward biasing of transis-
in turn, switches on a bulb to light up mains stepped down by transformer tor T3, which conducts to extend 3V
the path between the outer gate and X1 is rectified by diodes D1 and D2 battery supply to melody generator
the house door for a specific duration followed by filter capacitor C1. The DC UM66 (IC2). The output of the melody
(3 minutes). supply thus becomes available for generator drives transistor T3 to out-
Switch S2 (labelled ‘timer on’) is timer circuit comprising CD4060 (IC1) put the tune via loudspeaker LS1.
situated inside the house for use by and relay driver circuit comprising Thus, when a visitor presses switch
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2. CIRCUIT
IDEAS
S1 at the gate, the calling bell sounds sistor T1 conducts and T2 cuts off. between the gate and the house. It is
and the timer resets. The Q13 output The relay de-energises to turn the light decided by the values of resistor R4
of IC1 goes low to cut off transistor ‘off.’ and capacitor C3 as follows:
T1. Transistor T2 conducts to energise Since diode D5 is connected from ‘On’ period = 300xR4xC3 minutes
the relay and turn the light ‘on.’ Q13 to clock input terminal (pin 11), The light controller circuit will
When switch S1 is released, the the terminal is always high when Q13 work at night, provided mains switch
timer starts counting. After three min- is high, disabling the counting of IC1. S4 is ‘on.’ During night, only switches
utes (determined by resistor R4 (100- So the state is latched until the next S1 and S2 will be used, while switch
kilo-ohm) and capacitor C3 (0.1µF), resetting takes place. ‘On’ time period S3 is used in the day for the calling
the Q13 output goes high, i.e., tran- can be varied according to the distance bell only.
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CMYK