Automatic Street Light LDR

In this lesson today, we will learn how to design and construct Automatic streetlight using LDR.

A street lighting is any electrical lighting that is fixed outside house for the illumination of such environment, or a Street light is a raised source of light on the edge of a road or walkway, which is turned on or lit at a certain time every night. Automatic streetlight controller will automatically turn on streetlight in the way of LEDs or bulb coupled with relay. This system employed the output from an uncomplicated light/dark activated circuit and obliges a relay in its output which can be further attached to switch ON/OFF a streetlight and electrical application in a household also.

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below is the circuit and block diagram

Explanation of block diagram:

The circuit diagram of automatic streetlight control system using LDR are as follows, LDR senses the illumination level and gives the input signal as voltage drop. Amplifier: Darlington circuit amplifies the input current to get maximum current gain. Switch: Relay switch closes or opens electrically and automatically, which is energized or de energized by the Darlington pair. Streetlight: Street light is the output of the circuit. In this circuit, it has been replaced by LED.

 

Power Supply

The input to the circuit is applied from the regulated power supply. The A.C input i.e., 230V from the main supply is step down by the transformer to 12V and is fed to a rectifier. The output obtained from the rectifier is a pulsating D.C voltage. So in order to get a pure D.C voltage, the output voltage from the rectifier is fed to a filter to remove any A.C components present even after rectification. Now, this voltage is given to a voltage regulator to obtain a pure constant D.C voltage. 

Light Dependent Resistor 

(LDR) A Light Dependent Resistor (LDR) is a device which has a resistance which varies according to the amount of light falling on its surface. There are two basic circuits using LDR the first is activated by darkness, and the second is activated by light. The two circuits are similar and just require an LDR, some standard resistors, a variable resistor and any small signal transistor. Light Dependent Resistor contains cadmium sulphide track.

Principle of operation:

The automatic streetlight control system operates on 12 V DC supply from rectifier circuit. The automatic streetlight controller has a photoconductive device whose resistance changes proportional to the extent of illumination, which switches ON or OFF the LED with the use of transistor as a switch. Light dependent resistor, a photoconductive device has been used as the transducer to convert light energy into electrical energy. The central dogma of the circuit is that the change in voltage drop across the light dependent resistor on illumination or darkness switches the transistor between cut-off region or saturation region and switches OFF or ON the LED.

Working of streetlight:

This is a design for circuit diagram of a streetlight that automatically switches ON when the night falls and turns OFF when the sun rise. In fact, you can use this circuit for implementing any type of automatic night light. This circuit is based on the operation of an LDR system.  it uses an LDR to sense the light. The LDR offers Very low Resistance in brightness. In this case the voltage drop across the LDR is less than 0.7V. This voltage is more sufficient to drive the transistor into saturation region. When there is light the resistance of LDR will be low. So, the voltage drop across POT R2 will be high. This keeps the transistors Q1 ON. The collector of Q1 (BC 547) is coupled to base of Q2 (IRF44n). So Q2 will be OFF and so do the relay. The LED will remain OFF. When night falls the resistance of LDR increases to make the voltage across the POT R2 to decrease below 0.6V. This makes transistor Q1 OFF which in turn ON Q2. The LED will glow. The high collector current flowing through the relay, diode, LED and resistor makes the LED glow. When a light of suitable intensity is incident on the light dependent resistor, the resistance decreases, and the voltage drop across the light dependent resistor is low In POT R2 can be used to adjust the sensitivity of the circuit. In this project we have used one LED for indication. We Can use bulb of any wattage, provided with relay should have the sufficient rating. The circuit can be powered from a regulated 12V DC power supply.

Conclusion

This Lesson elaborates the design and construction of automatic light control system circuit. Circuit works properly to turn lamp ON/OFF. If the conditions have been satisfied the circuit will do the desired work according to specific program. The sensor controls the turning ON or OFF the lighting. The lights have been successfully controlled by IRF44N transistor. With commands from the switching circuit the lights will be ON.

See you guys in our next lesson. thank you