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How To Design An Automatic Street Light Controller Circuit With Gsm Device Using Relay And Ldr.

Importance of Street Lights

Accidents are more prone during the night and street lights tend to play a significant role in avoiding such accidents as well as improving the safety condition of a place. The provision of street lights has turned out to be one of such expensive responsibilities that the authority of a city is entrusted with. To the tune of between 10-38% of the energy bills in most of the cities is attributed to lighting. Street lighting has a direct impact on the economic and social stability of mostly the developing countries hence it has become of critical and special concern (Boylestad, 2013, p.201).

Through the fixtures of lights, the public and the government have been assisted in reducing the levels of crime rates as well as accidents in the areas in which they have been used. On the other hand, street lights help in fostering social inclusion through offering an environment in which there is freedom to walk even in the wee hours of darkness. The world of today is too busy to the extent that nobody bothers or other remembers to switch the street lights ON/FOFF when not needed. Significant financial resources go to waste as a result of inefficient lighting with poor lighting culminating into unsafe conditions. Through the use of energy-efficient technologies, it is possible to reduce the cost of street lighting in significant proportions.

Power consumption, automation, and cost-effectiveness form the main consideration in the current day technology (Molloy, 2014, p.245). Automation intends to use intelligent systems in a bid to reduce manpower which power saving and efficiency remain the main forever consideration owing to the fact that the energy resources and sources are getting depleted every day due to various reasons. In term of cost-effectiveness, the design of a system must be cost effective due to the unlimited requirements.

Overcoming the problems have resulted in the introduction of Automatic Street lighting control methods. The objective of this project is to offer a better alternative if not the best for the reduction of the electrical wastages in the operation o street lights in this generation where automation humans do not rest and are not able to manually regulate operations in any sector or field.

This project presents an automatic street light control system that makes use of a light dependent resistor and a relay. The use of this system eliminates the need of manual works as the street lights will be switched ON automatically as soon as the sun gets to levels that are lower than the region that is visible to the eyes. The systems automatically switch OFF the street lights when the sun is illuminating the side of the earth. Presented herein is a simple yet powerful concept that is used in the switching ON/OFF of street lights (McKinlay, 2016, p.269).

Current Day Technology

When the sun gets to below the visible region of the eyes, the street lights are automatically switched ON while an ample amount of sunlight availability switches the street lights OFF automatically.  A light dependent resistor is used as the light sensing device. The use of light dependent resistor allows automatic operation on the streetlights in such a way that the street lights will be in the OFF mode when there are enough amounts of sunlight available and ON mode when there is darkness (Braga, 2011, p.114). The operation of the light dependent resistor is such that its resistance is inversely proportional to the intensity of light that falls on it.

Upon light falling on the light dependent resistor, signals or commands are sent to the control circuit commanding the street light to be OFF. Th project takes advantage of the operation of a transistor in both saturation and cut-off regions in switching ON and OFF the lights as deemed appropriate with the aid of switch that is operated by a magnet.

The operation of the system in line with the variation in sunlight such that during the day when there is enough sunlight hitting the LDR, the resistance is high and thus acting as an insulator while during darkness the LDR has a low resistance path thereby permitting the flow of electricity (Mazidi, 2014, p.368).  The ATmega8 microcontroller performs the switching action of street light alongside a relay driver circuit. A controlled 5V DC is needed for the whole control circuit in order to operate. A step-down transformer is included in the system to step down the 230V AC to 12V AC which is then converted to 5V DC using a bridge rectifier. The regulated output from the voltage regulator is then set to the control unit for use in its operation.

 A Light Dependent Resistor is of great importance especially in sensor circuits that are controlled by light or darkness. The resistance of Light Dependent Resistor is usually very high, as high as 1000000 ohms at times which drops tremendously when illuminated with light. Photosensors are devices which are capable of changing their characteristics in the presence of light adding such devices include phototransistors, a light dependent resistor as well as a photodiode. Just as the name goes, light dependent resistance relies on light to change their resistance (Breithaupt, 2015, p.154). They are made of a film of cadmium selenide or cadmium sulfide that is deposited on a ceramic substrate which is composed of no or very little electrons upon illumination. When the strip is long, the resistance tends to be higher. The resistance decreases when the strip is illuminated with light.

Automatic Street Lighting Control Methods

The light depended resistor applies the principle of photoconductivity. The moment light falls on the LDR its conductivity decreases while the electrons which are in the valence band are triggered to move to the conduction band (Horowitz, 2015). The photons which the incident light is having must possess energy which is more than the semiconductor bandgap this results in the electrons moving to the conduction band from the valence band.

These devices depend on the nature of the light. The moment lands on the light dependent resistor the resistance decreases and when the amount of light falling on the surfaces decreases the resistance increases. When the light depended resistor is kept in darkness its resistance is high and when it is kept in light its resistance decreases (Braga, 2011, p.282).

The figure below shows the circuit diagram of the light dependent resistor. The resistance of the LDR is high when the light intensity is low, which halts the flow of current to the base terminal of the transistor thereby making the bulb to go off. Nevertheless, the resistance of the LDR is low when the light intensity is high, which makes the current to flow to the base of the first transistor then afterward the secondary transmitter which results to the bulb lighting (Breithaupt, 2015, p.634). The present resistor, in this case, is used to turn down or up to decrease or increase the resistance.

The following are the feature of an LDR:

  • Lightweight
  • Wide ambient temperature
  • High reliability
  • Wide spectral response(Devlin, 2015, p.177)
  • Components of the regulated Power Supply

The following are the basic building blocks of a controlled DC power supply:

  • DC filter
  • Step down transformer(Kamal, 2009, p.258)
  • Rectifier
  • Voltage regulator

The step-down transformer is used in converting 230V; 50 Hz AC to 5 V. This is achieved through giving the alternative voltage that comes from the second terminal of the transformer to the bridge rectifier. The voltage is then fed into a regulator of 5V through the electrolytic capacitor which removes the ripples thereby creating a stable output. A 5V DC is therefore achieved after regulation of the voltage at the 7805 IC output (Boylestad, 2013, p.137).

Among the features of ATmega8 microcontroller include 8KB In-System Programmable Flash that has Read-While-Write abilities, 512 bytes EEPROM, 23 I/O modes of general purpose, 1 KB SRAM, Timer, SPI port among other features.

Advantages of ATmega8 microcontroller

  • Has an additional EEPROM that stores data in power off time
  • An interrupt can be generated through both changes of the level of output
  • Faster instruction time than 8051
  • Uses RISC instruction sets
  • Built using two various architectures
  • Ease of programming AVR

Aim: To design and implement a system of control of street light that is automatic using light dependent resistor and relay


  • Explore the current street light control systems
  • Design a street light control system that is efficient
  • Come up with the hardware control unit
  • Test and confirm the validity of the designed system

Objective 1 methodology

  • Exploration into the existing literature will be made so as to enable an in-depth comprehension of the current street light controls systems. The literature will be analyzed to come up with the limitations of the existing street night control systems that will also form the basis of the need for their elimination.

Objective 2 Methodology

  • The design of the street light control system will be done in line with the specifications.
  • MULTISIM will be used in simulating the designed control circuit to establish its workability and the various characteristics will be noted.
  • The design will undergo further refining so as to achieve the desired features and then retesting will be done using MULTISM

Objective 3 Methodology

  • The choice of the appropriate components of the control unit will be chosen and the final design fabricated.

Objective 4 Methodology

  • Observations will be made on the working of the fabricated control circuit system and the notable features recorded.
  • The benefits and advantages of the new design will be tested and validated against the efficiency and performance of the existing systems.
  • Conclusions will be made based on the validation studies attained.

Design of the Automatic Street Light Control System

The emphasis of this project is on the development of an automatic street light control system that is cost-effective as well as reliable. The main disadvantage of the existing switching and timer switching systems is linked to power wastage. The main concern here, therefore, is to come up with an automatic street controller system that is highly reliable (Gajjar, 2015, p.278).

The whole controlling unit will be controlled by the ATmega8 microcontroller. This controller needs 5V DC in order to operate which will be obtained from a rectifier circuit. The rectifier circuit is also inclusive of a voltage regulator and a step-down transformer. The light dependent resistor that is used in this experiment as a light sensing device is used in sending analog signals to the microcontroller for interpretation. The four button keyboard alongside the liquid crystal display is used in setting the real-time, OFF time and ON time settings. A period of one hour is provided as the tolerance to allow efficient working of the streetlight (Mazidi, 2014, p.327).

Two conditions must be satisfied in order to switch the streetlights OFF/ON. The light intensity sensing of the light-dependent diode is one such condition while the other is the timers sued in the microcontroller. Upon the achievement of these conditions, the microcontroller is able to produce control signals that are used to energize or de-energize the relay that is used in switching ON/OFF the street lights.

The ATmega8 microcontroller has an Analog to digital converter that is used in conveying the analog signals sent by the light dependent resistor to digital signals. Setting of the real-time and On/Off time is done and a one hour tolerance is preset with the aid of codes that are written using the C programming language (McKinlay, 2016, p.167). This program is then dumped into the microcontroller for processing.  The ATmega8 microcontroller controls the operations of the Relay switch.

The power wastages that have been identified as the main drawback of the conventional street light control system are attributed to the improper operation of the switching system. This project thus aims at developing automatic streetlight systems that are very reliable in terms of reduction of wastages of power. The automat control unit that has been designed is composed of a microcontroller that has been used as the main component that controls the whole system alongside a Light Dependent Resistor. The designed system is found to demonstrate a highly reliable and efficient automatic switching system which addresses the challenge of the conventional switching system (Zheng, 2009, p.298).

The constructed system as shown in the figure below is a circuit of an automatic street light control. The project includes designed systems such as codes that are written in C programming language and the dumped into the ATmega8 microcontroller. In the ATmega8 microcontroller, the analog signals that come from the Light Dependent Resistor are analyzed and the keyboard LCD display is used in doing the settings of the ON/OFF time settings. The streetlights will turn ON/OFF only upon attaining the conditions described (Kamal, 2009, p.189).  


Boylestad, R.L., 2013. Electronic Devices and Circuit Theory. 11th ed. New York: Pearson Education.

Braga, N.C., 2011. Robotics, Mechatronics, and Artificial Intelligence: Experimental Circuit Blocks for Designers. 6th ed. Paris: Elsevier.

Breithaupt, J., 2015. New Understanding Physics for Advanced Level. 3rd ed. Chicago: Nelson Thornes.

Devlin, P.M., 2015. Brachytherapy, Second Edition: Applications and Techniques. 2nd ed. Oxford: Springer Publishing Company.

Gajjar, R., 2015. Raspberry Pi Sensors. 7th ed. New York: Packt Publishing Ltd.

Horowitz, P., 2015. The Art of Electronics. 3rd ed. Cambridge: Cambridge University Press.

Kamal, R., 2009. Microcontrollers: Architecture, Programming, Interfacing and System Design. 3rd ed. London: Pearson Education India.

Mazidi, M.A., 2014. 8051 Microcontroller and Embedded Systems, The: Pearson New International Edition. 2nd ed. Sydney: Pearson Education Limited.

McKinlay, R., 2016. PIC Microcontroller and Embedded Systems: Using Assembly and C for Pic18. 3rd ed. Moscow: MicroDigitalEd.

Molloy, D., 2014. Exploring BeagleBone: Tools and Techniques for Building with Embedded Linux. 4th ed. London: John Wiley & Sons.

Zheng, J., 2009. Wireless Sensor Networks: A Networking Perspective. 4th ed. Beijing: John Wiley & Sons.

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