1.       Introduction

In the contemporary context of escalating energy demands and growing environmental consciousness, the need for intelligent energy management systems has become paramount. Lighting accounts for a substantial portion of total electricity consumption in residential, commercial, and institutional buildings. Conventional lighting systems rely heavily on manual operation, which frequently results in lights being inadvertently left on in unoccupied rooms, leading to considerable energy wastage and increased operational costs [1], [2]. The integration of automation technologies into everyday infrastructure offers a viable pathway toward mitigating such inefficiencies. Automatic lighting control systems, which activate illumination only when human presence is detected, represent a practical and impactful application of sensor-based automation. Among various motion detection technologies, Passive Infrared (PIR) sensors have emerged as a preferred choice due to their low power consumption, affordability, ease of integration, and reliable performance in detecting human movement within confined spaces [3].

This paper details the design, implementation, and evaluation of an automatic room light controller based on a PIR sensor. The primary objectives of this work are: (i) to develop a low-cost, reliable system that eliminates manual light switching; (ii) to reduce unnecessary energy consumption by ensuring lights are active only when a room is occupied; (iii) to provide a scalable solution that can be deployed across diverse indoor settings; and (iv) to demonstrate the practical application of fundamental electronic components—including sensors, transistors, relays, and diodes—in addressing real-world energy challenges.

The remainder of this paper is organized as follows: Section II describes the system architecture and component specifications. Section III presents the hardware implementation and prototype development. Section IV discusses the results and performance evaluation. Section V concludes the paper with recommendations for future enhancements.

2. System architecture and components

2.1. Overall System Design

The proposed automatic light control system employs a modular architecture comprising four functional blocks: (1) motion sensing unit, (2) signal conditioning and switching unit, (3) load control unit, and (4) power supply unit. Figure 1 illustrates the block diagram of the system. The PIR sensor serves as the input transducer, converting infrared radiation emitted by the human body into an electrical signal. This signal is processed and used to drive a transistor operating in switching mode. The transistor, in turn, controls a relay module that isolates the low-voltage control circuitry from the AC lighting load. A 5V charging module provides regulated power to the sensor and control logic.

2.2. Component Specifications and Selection

1) PIR Motion Sensor

The PIR sensor is the core detection element of the proposed system. It operates on the principle of passive infrared detection, sensing changes in infrared radiation levels within its field of view. The sensor contains a pyroelectric sensing element divided into two halves, configured in a differential arrangement that cancels out ambient infrared levels while responding to changes caused by moving heat sources—primarily human bodies. Key advantages include low power consumption (typically 50–100 µA), low cost, compact form factor, and absence of moving parts, ensuring long-term reliability [4], [5].

Specifications: Operating voltage: 5V DC; Detection range: up to 7 meters; Detection angle: up to 110 degrees; Output: digital (HIGH when motion detected).

2) BC547 NPN Transistor

The BC547 is a general-purpose NPN bipolar junction transistor (BJT) widely used for low-power switching and amplification applications. In this design, the transistor operates in the cut-off and saturation regions, functioning as an electronic switch. When the PIR sensor output goes HIGH, the base-emitter junction becomes forward-biased, driving the transistor into saturation and allowing collector current to flow, which energizes the relay coil. The BC547 offers a maximum collector current of 100 mA, a collector-emitter voltage rating of 45V, and a DC current gain (hFE) ranging from 110 to 800, making it well-suited for this application [6].

Pin Configuration: Collector (C), Base (B), Emitter (E).

3) Relay Module

A 5V active-high relay module is employed to interface the low-power control circuitry with the AC lighting load (230V, 50Hz). The relay provides electrical isolation between the two domains, protecting the sensitive electronic components from high-voltage transients. The module includes an optocoupler for additional isolation, a transistor driver, and a flyback diode to suppress inductive kickback from the relay coil. The relay contacts are rated for 10A at 250V AC, sufficient for standard lighting loads [7].

4) 5V Charging Module

A compact 5V DC-DC converter module provides regulated power to the PIR sensor and transistor circuit. The module accepts input from a standard USB power source or a rechargeable battery (3.7–5V) and delivers a stable 5V output. It incorporates overcurrent and short-circuit protection features, ensuring safe operation.

5) 1N4007 Diode

The 1N4007 is a general-purpose silicon rectifier diode with a peak repetitive reverse voltage rating of 1000V and an average forward current rating of 1A. In this circuit, it is used as a flyback diode connected in parallel with the relay coil to suppress voltage spikes generated during coil de-energization, thereby protecting the switching transistor from damage [8].

2.3. Circuit Operation Principle

The operational logic of the system is as follows:

1.         Standby State: In the absence of motion, the PIR sensor output remains LOW (0V). The BC547 transistor is in cut-off mode, no current flows through the relay coil, and the relay contacts remain open. The AC lighting load is disconnected from the mains supply, and the light remains OFF.

2.         Motion Detection: When a person enters the detection zone, the PIR sensor detects the change in infrared radiation and drives its output HIGH (approximately 5V). This HIGH signal is applied to the base of the BC547 transistor through a current-limiting resistor.

3.         Transistor Switching: The base current forward-biases the base-emitter junction, driving the transistor into saturation. Collector current flows from the 5V supply through the relay coil to ground, energizing the coil.

4.         Load Activation: The energized relay coil generates a magnetic field that pulls the relay contacts closed, completing the AC circuit and turning ON the connected light.

5.         Time Delay and Deactivation: After the person leaves the detection zone, the PIR sensor output returns to LOW after a preset delay (typically 5–30 seconds, adjustable via onboard potentiometer). The transistor returns to cut-off, de-energizing the relay coil. The contacts open, and the light turns OFF automatically.

2.4. Cost Analysis

Table 1 presents the detailed cost breakdown of the prototype components. The total cost of ₹400 demonstrates the economic viability of the proposed system, making it accessible for widespread deployment in resource-constrained settings.

Table 1. Cost and specifications

3. Hardware implementation

3.1. Prototype Development

The complete hardware prototype was assembled on a breadboard for initial testing and subsequently transferred to a perforated board (PCB) for permanent implementation. Figure 2 shows the circuit schematic diagram, and Figure 3 presents the complete hardware model.                

Fig. 2. Circuit Schematic Diagram

Fig. 3. Complete Hardware Model

The assembly process involved the following steps:

1.       The PIR sensor was positioned to provide optimal coverage of the target area, with the sensitivity and time delay potentiometers adjusted to desired settings.

2.       The BC547 transistor was mounted with proper orientation (collector, base, emitter identified).

3.       A 1kΩ resistor was connected between the PIR output and the transistor base to limit base current.

4.       The relay module was interfaced with the transistor collector, with the flyback diode (1N4007) connected across the relay coil terminals (cathode to VCC, anode to collector).

5.       The 5V charging module was connected to provide regulated power to the PIR sensor and the relay coil supply.

6.       The AC lighting load (9W LED bulb) was connected to the normally open (NO) and common (COM) terminals of the relay.

7.       The complete assembly was enclosed in a protective housing with appropriate ventilation.

3.2. Testing and Calibration

The system was tested under various conditions, including different ambient temperatures, distances from the sensor, and movement speeds. Calibration of the PIR sensor involved adjusting:

·         Sensitivity Potentiometer: To set the detection distance (3–7 meters).

·         Time Delay Potentiometer: To set the output HIGH duration after motion ceases (5–300 seconds).

Optimal performance was achieved with sensitivity set to approximately 5 meters and time delay set to 30 seconds.

Fig. 4. Replica of Final Hardware Model

4. Results and discussion

4.1. Functional Performance

The prototype was subjected to 100 test cycles under controlled conditions. The system successfully detected human presence and activated the light in 98% of trials. The two failure instances were attributed to the user moving outside the sensor's detection angle. Once motion ceased, the light automatically turned off after the preset 30-second delay in all cases. The response time from motion detection to light activation was consistently below 1 second.

4.2. Energy Savings Estimation

To quantify the energy-saving potential, consider a typical classroom (10 hours of daily usage) where lights are inadvertently left on for 2 hours per day when unoccupied. A standard 40W fluorescent tube consumes 0.08 kWh during this period. Over 200 working days annually, this amounts to 16 kWh wasted per classroom. At an electricity tariff of ₹7 per kWh, this represents an annual saving of ₹112 per classroom. For an institution with 50 classrooms, the annual saving exceeds ₹5,600, while the implementation cost per room is only ₹400—yielding a payback period of less than 9 months.

4.3. Comparison with Existing Systems

Table II compares the proposed system with conventional lighting and other automated solutions.

Table 2. Comparative analysis

The proposed system offers comparable functionality to commercial motion sensors at approximately 15–25% of the cost, making it particularly attractive for budget-constrained applications.

4.4. Limitations

The following limitations were identified during testing:

1.       Limited Detection Zone: The PIR sensor cannot detect stationary individuals, as it responds only to changes in infrared radiation. A person remaining perfectly still may not maintain the light in the ON state.

2.       False Triggers: Rapid temperature fluctuations or moving non-human heat sources (e.g., pets, direct sunlight) occasionally caused false activations.

3.       No Ambient Light Sensing: The system activates lights regardless of ambient illumination levels, which may be inefficient during daylight hours.

5. Conclusion and future scope

5.1. Future Enhancements

The following enhancements are recommended for future iterations of the system:

1.       Integration of Photoresistor (LDR): Incorporating a light-dependent resistor (LDR) would enable the system to activate lights only when both motion is detected AND ambient light falls below a threshold, further improving energy efficiency during daylight hours.

2.       Bluetooth/Wi-Fi Connectivity: Adding a Bluetooth module (e.g., HC-05) or Wi-Fi module (e.g., ESP8266) would enable remote monitoring and control via smartphone applications, allowing users to override automatic operation or receive notifications.

3.       Microcontroller-based Control: Replacing the discrete transistor switch with an Arduino or similar microcontroller would enable programmable timing, multiple sensor inputs, and data logging capabilities.

4.       Multi-Sensor Integration: Deploying multiple PIR sensors in a network could extend coverage to larger areas and reduce false negatives.

5.       Solar Power Integration: Coupling the system with a small solar panel and battery storage would enable off-grid operation, particularly beneficial for rural or remote installations.

5.2. Applications

The proposed system is well-suited for the following applications:

·         Educational Institutions: Classrooms, laboratories, libraries, and corridors.

·         Residential Spaces: Bathrooms, staircases, basements, and storage rooms.

·         Commercial Buildings: Conference rooms, washrooms, and break rooms.

·         Healthcare Facilities: Patient rooms and corridors (with appropriate isolation).

·         Hospitality Sector: Hotel corridors and guest bathrooms.

5.3. Conclusion

This paper has presented the successful design, implementation, and testing of a low-cost automatic light control system using a PIR sensor. The system effectively eliminates manual switching, reduces energy wastage by ensuring lights are active only when human presence is detected, and offers a practical solution for diverse indoor applications. With a total component cost of ₹400, the system is economically viable and can be deployed in educational institutions, residential buildings, bathrooms, staircases, and other spaces where manual lighting control often leads to inefficiency. The prototype demonstrated reliable performance with a 98% detection success rate and sub-second response time.

Acknowledgment:

The authors express their sincere gratitude to Prof. (Dr.) Pankaj Jha, Head of the Department of Electronics and Communication Engineering, IIMT College of Engineering, Greater Noida, for his invaluable guidance, encouragement, and support throughout this project. The authors also thank all faculty members and technical staff who provided assistance during the design and testing phases. Finally, the authors acknowledge their B.Tech. batchmates for their constructive feedback and collaborative spirit.