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When
any person tries to enter the gate, the light beam falling on
the LDR1 is momentarily interrupted. As a result IC 1,
configured as monostable flip-flop, gets a trigger pulse at
its trigger input 2. Its out goes high for a predetermined
time period. The period can be adjusted by varying the value
of resister R1 or capacitor C1 as T=1.1*R1*C1 sec.
Output pulse from IC 1 forward biases the transistor T1. As a
result the musical bell is switched ON. The musical bell is
built around IC 2(UM 66). The output from IC 2 is amplified by
transistor T2 to drive an 8-ohm, 500mW-load speaker. IC 2 is
also gets trigger pulse at its trigger input when IC 1 gets
trigger at its trigger input because trigger input pin 2 of IC
1 and IC 2 are shorted. Therefore its out goes high for a
predetermined time period. The period can be adjusted by
varying the value of resister R2 or capacitor C2 as
T=1.1*R2*C2 sec. Output pulse from IC 2 forward biases
transistor T3 and relay R1 is energized, but the bulb is
switched ON only at night.
An
LDR based circuit is used to switch ON the bulb at night only.
The bulb is switched ON when relay R1 and R2 are energized.
Relay R1 and R2 are connected in series with bulbs to the
power supply. Two relays are like two switches of the bulb.
During day time LDR offers a very low resistance, and thus the voltage pin 2 of IC 4 is more than 1/3 Vcc, so that its output goes low and the relay R2 is de-energized. These results in
opening of power supply contact to the bulbs and thus
switching OFF the bulbs. During the night time the dark
resistance of LDR is very high, and thus the voltage at pin 2
of IC 4 is less than 1/3 Vcc, so that its output goes low and
the relay RL 2 is de-energized. These results in shorting of
power supply contact to the bulbs and thus switches ON the
bulbs.
Water
level indicator and controller
Generally overhead tanks are filled with water by operating a
pump. We have no control over the level to which it may be
filled. It may cause overflow or water level may remain too
low when we switch OFF the pump motor. Manual operation of the
motor pump starter is thus not advisable. Present circuit may
be added to the existing manual starter of the pump motor so
that it may be operated automatically.
Four
sensor probes made up of brass or stainless steel stiff wires
or rods may be hung firmly in the tank. This indicates the
water level in the water tank at four steps F, H, L, E i.e.,
Full, Half, Low, Empty. When there is no water in the water
tank the circuit automatically switches ON the pump and
switches OFF when the water level comes to Full.
Probes marked E and L are hung with their bottoms near the
bottom level of the tank at which we wish to start the pump.
The probe F is hung with its bottom end in between those
probes E and F. It is used for indication of the middle level.
Sensor H, L, F are connected with resistors R1, R2, and R3,
where as probe E is directly connected to ground. Resistors
R1, R2, R3 are connected to 12V supply through resistors R4,
R5 and R6 respectively.
Working:
When
the water level in the tank is below probes E and L, output of
gate N9 is logic low and output of gate N12 is latched to
logic high level. Simultaneously output of gate N11 goes logic
low and is inverted by inverter. Now the output of gate N10
becomes logical high, and thus the transistor is forward
biased to ON state and the relay is energized. These results
in shorting of power supply contact to the pump and thus
switching ON the pump motor.
As
the water starts filling in the tank and ultimately touches
probe F, the output of gate N11 goes high and is inverted by
inverter. Now the output of gate N10 becomes logical low, and
thus the transistor is reverse biased to OFF state and the
relay is de-energized. These results in opening of power
supply contact to the pump and thus switching OFF the pump
motor.
Water
level states are displayed using IC 5 and IC 6 in conjunction
with 7-segment display. The display indicates F for Full, H
for Half, L for Low and E for Empty level condition.
Remote
control unit
This
unit replaces the conventional switch boards. Fans, light and
other equipments can be operated and controlled using remote
control unit. Also, this unit can be used for opening and
closing the gates at the pressing of a button on the remote
control.
This
circuit has two stages: a transmitting unit and a receiver
unit. The transmitting unit consisting of an infrared LED and
its associated circuitry. The receiving unit consists of a
sensor and its associated circuitry. The IR LED emit infrared
light switch is put on in the transmitting unit. To generate
IR signal 555 IC based astable multivibrator is used. Infrared
LED is driven through transistor BC 177.
In
receiver section, the first part is a sensor, which detects IR
pulses transmitted by IR-LED. When any key on the remote
control handset is depressed, the output of IR sensor
momentarily transits through low state. As a result the
monostable is triggered and a short pulse is applied to the
clock input (pin 14) of IC 7493, which is a counter IC. Thus
Q1 output (pin1 &12) of IC 7493 becomes high and transistor T2
is forward biased to ON state and the relay is energized.
These results in shorting of power supply contact to the bulbs
or any equipments and thus switching ON the bulbs or any
equipments.
Touch sensitive burglar alarm for internal security
This
simple circuit when connected to a metal locker or cupboard
generates an alarm when touched by an undesired entity.
The
transistor gets saturated by just touching its base. Here is a
simple, low cast touch switch with alarm based on this idea.
The 50 Hz hum present in our body is the key to this circuit.
BC 549 transistor has been chosen for this circuit. The
circuit is basically a burglar alarm with timer. Timer circuit
is a monostable multivibrator. Initially voltage at pin 2 of
IC 1 is low.
If
the sensor, which is the base of the transistor T1 is touched
by the finger (even the slightest, touch will do) transistor
T1 is saturated. Now the voltage at pin 2 of IC 1 is greater
than 1/3 Vcc. As a result IC 1 gets a trigger pulse at its
trigger input pin 2. Therefore its out goes high for a
predetermined time period. The period can be adjusted by
varying the value of resistor R1 or capacitor C1 as
T=1.1*R1*C1 sec.
The siren circuit is build around IC 2 (UM 3561).
Since the output of IC 1 is high, the IC 2 gets power supply.
The output from IC 2 is amplified by transistor to drive an
8-ohm, 500mw load-speaker.
For queries on the above please
contact
ranjith@electrofriends.com
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by
Ranjith Yadapadithaya
ranjith@electrofriends.com
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