This document describes an automatic street light control circuit using an LDR (Light Dependent Resistor). The circuit uses an operational amplifier IC CA3140 to compare the voltage from a potential divider using the LDR and a variable resistor, to a fixed voltage from another potential divider. During the day when light falls on the LDR, its resistance is low and the LDR voltage is higher, turning the lights off. At night when resistance is high, the LDR voltage decreases below the fixed voltage, turning the lights on. The circuit automatically controls street lights based on ambient light levels measured by the LDR to efficiently use energy.

2. Automatic Street Light control using
LDR

3. GROUP MEMEBERS
M Asif UW-13-ME-BSC-052
Jawad Arshad UW-13-ME-BSC-056
Ahsan Nasim UW-13-ME-BSC-092

4. Circuit diagram

5. COMPONENTS
 IC
 Resistor
 Variable Resistor
 Capacitor
 LDR
 Transistor (BC548)
 Relay
 LED

6. WORKINGWORKING
• 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).

7. • 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.

8. • 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.

9. PROTEUS IMPLEMENTATIONPROTEUS IMPLEMENTATION

10. AdvantagesAdvantages
No man power required.No man power required.
Simple Construction.Simple Construction.
Efficient method.Efficient method.
 Less Consumption of electrical energy.Less Consumption of electrical energy.
Less maintenance.Less maintenance.
Cheap and economical.Cheap and economical.