Many of the people have a phobia of darkness, so to assist them in such situation, we have explained a simple circuit. It will automatically turn on street light in the way of LEDs or bulb coupled with relay. Working this circuit is very much easy and also the power consumed by the circuit is very low because of the very few components used in the circuit.
LDR is a device whose sensitivity depends upon the intensity of light falling on it. When the strength of the light falling on LDR increases the LDR resistance decreases , while if the strength of the light falling on LDR decreased resistance incresed. In the time of darkness or when there is no light, the resistance of LDR is in the range of mega ohms, while in the presence of light or in brightness in decrease by few hundred ohms.
Automatic control of street light using LDR
Automatic Street LightAutomatic Street Light
control using LDRcontrol using LDR
Compiled by :
Changela Savan IU124106008
Kavathiya Mit IU124106020
Loharikar Devang IU124106023
Zala Ajay IU124106062
Planning of Project
Description of Hardware
Many of the people have a phobia of
darkness, so to assist them in such situation,
we have explained a simple circuit. It will
automatically turn on street light in the way of
LEDs or bulb coupled with relay. Working this
circuit is very much easy and also the power
consumed by the circuit is very low because
of the very few components used in the
Description of Hardware :
on intensity of light.
Resistance of LDR
increase in intensity of
light and vice-versa.
It is a passive component having two terminals that
are used to manage the current flow in the circuit.
A current that flows via a resistor is directly
proportional to the voltage that appeared into resistor.
(1) Fixed value resistor
(2) Variable resistor
The CA 3140 is an operational amplifier can
works on supply voltage 4V to 36V & very
low input current from 10pA to 1mA.
Here, The CA3140 works as a comparator
and gives fast response &high speed.
Relays is an electrically operated switch.
Current flowing through the coil of the relay
creates a magnetic field which attracts a
lever & changes the switch contacts.
It has 3-pin,4-pin,5-pin etc…but we have
used 5-pin in our circuit diagram.
Relay offers easy way for LED to indicate a
voltage is present at Relay coil.
As no input state,
the COM is connected
To NC & when operating
V is applied to relay coil
Gets energized &COM
Is now with NO.
(5) BC548 Transistor :
It is a general purpose silicon, NPN, bipolar
junction transistor. It is used for amplification &
Here, for switching purpose it is
biased so that it remains on if
there is signal at its base , other-
wise it is completely off.
Working of Automatic Street Light
Controller Switch Circuit:
The working of circuit is very much easy to
understand. In this circuit, we used IC
CA3140 which is basically an operational
amplifier. Pins 2 and 3 of these IC are used
to compare the voltage and give us the
output in return i.e. it works as a potential
divider in its inverting and non-inverting
inputs (pins 2 and 3).
In this LDR and VR1 form one potential
divider which is used to provide a variable
voltage at the inverting input (that is 2) and
the second potential divider is built around
non-inverting input (pin 3) with the help of R1
and R2 which will grant half of the supply
voltage to non inverting pin.
As we know property of LDR that during the
time of day resistance is low therefore
voltage at the inverting input ( IE pin 2) is
higher than the voltage at the non-inverting
input (pin3) hence the output at the pin6 is
low so the transistor goes into the cutoff state
which means LED or bulb will not glow.
But in dimness or in night we know that
resistance of LDR is high hence voltage at
inverting input pin 2 of the IC CA3140 decreases
than the non inverting input pin 3 as a result
output pin 6 moves to high state which make
transistor to conduct and the LED or bulb
associated to it start simmering.
No man power required.
Less Consumption of electrical energy.
Cheap and economical.
In coming days, this will prove a great boon
to the world, since it will save a lot of
electricity of power plants that gets wasted in
illuminating the street lights. As the
conventional sources are depleting very fast,
then it`s time to think of alternatives.