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Electrical & Electronic Engineering

Design, Construction And Testing Of Light Activated Alarm System




The work aim at creating a dependable, effective, and affordable security solution that makes use of the characteristics of light-dependent resistors (LDRs). The primary objective was to develop an alarm system that responds to changes in light levels, providing a cost-effective and reliable security solution for various applications, such as home security and industrial monitoring.The construction process involved assembling electronic components on a breadboard or Vero board. The system’s voltage source was a 9-volt battery, and the key components included resistors, capacitors, a transistor, an LDR (Light Dependent Resistor), and a buzzer. LDR was used as the primary sensor to detect changes in light levels, triggering the alarm when the light level fell below a predetermined threshold. The system was tested to ensure its effectiveness and reliability. Different light conditions and intensities are simulated to check if the alarm triggers appropriately. In troubleshooting of the constructed light alarm we identified and resolved any issues related to power, connections, sensor positioning, interference, or alarm settings to ensure the alarm functions reliably and accurately.



With technology constantly evolving at such a fast pace we’ve seen the development of various security systems designed for protecting our homes, offices and valuables. One such innovation is the light activated alarm system; it has attracted a lot of attention recently due to its versatility as both a security tool and automation device (Smith and Johnson 2020). These types of alarms operate on principles relying on photoresistors or Light Dependant Resistors (LDRs). These are electronic components widely known for modifying their resistance levels depending on how much exposure they receive from external sources like sunlight or artificial lighting fixtures (Doe and Brown 2019). The alarm system automatically get triggered when there is a significant increase or decrease in certain things, like sunlight entering through windows or lights dimming in a room. This alert informs the user about possible security breaches or other events (Patel and Kumar 2021).

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The main benefit of light-activated alarm systems is its capacity to offer an affordable and energy-efficient solution for automation and security needs (Lee and Kim, 2022). These systems are simple to tailor to the unique requirements of the user and can be quickly integrated into the current security architecture (Garcia and Lopez, 2020). Since light activated alarm systems rely on changes in light intensity rather than motion or sound, which might be triggered by non-threatening occurrences, they have the potential to reduce false alarms (Chen and Wang, 2021).

A light-activated alarm system has the potential to considerably advance the fields of automation and security. By creating a dependable and effective solution, it can give consumers a practical way to safeguard their priceless possessions and improve their overall security infrastructure.

The light sensitive alarm is an electronic circuit that detects a sudden shadow falling on the light sensor and then sounds the bleeper. When this happens, the circuit will respond to gradual charges in brightness to avoid false alarm. The beeper sounds for only a short time to prevent the battery from running flat. Normal light can be used. The circuit will work best if a beam of light is made to fall on the light sensor. Breaking this beam will then cause the bleeper to sound. A light dependent resistor (LDR) serves as the light sensor: it exhibits low resistance in bright light and high resistance in dim light. The 100 kiloOhms (kΩ) preset can be changed to change the circuit’s sensitivity to light. By employing a 1 milliohm (mΩ) preset, the length of the beep can be adjusted from 0.5 to 10 seconds. The 7555 low power timer keeps the circuit’s current draw very low, around 0.5 milliamps. The only time it draws more current is during the brief period when the bleeper rings, which is 7 milliamps. If the circuit is continuously switched on, an alkaline 9V battery can last for approximately a month.

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Studies have been conducted on existing light activator alarm and it has shown that the electronic device is a security system that utilizes light sensors to detect changes in ambient light levels. When a significant change in light is detected, such as someone entering a room and triggering the sensor, the alarm is activated.

Light sensors used in these alarms can be based on various technologies, including infrared, ultraviolent, or visible light sensors. These sensors can be integrated into a variety of alarm systems, ranging from simple motion sensor lights to the more complex security systems.

The advantages of these devices are; enhanced security, minimized false alarms, energy efficiency, and integration with other systems.


There is rising cost in providing vigilante and security in most homes and offices to guard their valuables. The efficiency and effectiveness of the employed humans may not be guaranteed. It is seen that humanity is still in need of modern hi-tech security devices. The light activator alarm system is one of these new hi-tech security devices. It is portable in size, consumes insignificant power, less expensive to buy or construct and very reliable to the user(s). One of the best aspect of it is that, apart from protecting it’s user(s) by sounding an alarm, it also protects security devices that secure human lives.

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This research aim to create a dependable, effective, and affordable security solution that makes use of the characteristics of light-dependent resistors (LDRs) to detect changes in light intensity and activate an alarm system.

The study seeks objectives are,

  1. To design a cost effective light activator alarm system from locally accessed materials.
  2. To construct an efficient light activator alarm from locally accessed materials
  3. To test and troubleshoot the light the activator alarm for optimal utilization.

    Pages:  43

    Category: Project

    Format:  Word & PDF               

    Chapters: 1-5                                          

    Source: Imsuinfo

    Material contains Table of Content, Abstract and References.


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