Project Hub /Security Surveillance & Defense/Intrusion Detection Systems/Build your own PIR Motion Sensor Light

Intermediate

ANALOG / DISCRETE

Project Specific

3 – 6 Hours

Partial Kit

Build your own PIR Motion Sensor Light

Learn how to build a microcontroller-free PIR motion sensor light using a PIR sensor, a BC547 transistor, a relay, and a 12V LED strip.

Originally published on CircuitDigest

View original tutorial

Parts You'll Need

This project is sourced from another site, not written by us — this list is our best match of their components against what we stock, not a verified bill of materials. Always check the original blog (linked above) for the actual parts list before buying.

PIR Motion Detector Sensor Module HC-SR501 Rs. 95.00
5V 1 Channel Relay Module Rs. 45.00
10pcs - 220 ohm 1/4 W Resistor Set Rs. 39.00
Jumper Wire 10 Pin Male To Male 20cm Rs. 45.00
MB102 Adjustable Breadboard Power Supply Module (3.3V & 5V) for Arduino & Raspberry Pi Rs. 139.00
400 Points Mini Solderless Prototype PCB Breadboard High Quality Rs. 89.00
Jumper Wire 10 Pin Male To Female 20cm Rs. 45.00

Selected: Rs. 0.00

This list includes a generic resistor set as a placeholder — it is not matched to the exact value or part number this circuit needs. The correct one is specified on the original source page linked above; check it before buying.

We don't carry yet: Transistors (BC547 / 2N2222 / TIP / MOSFET)
LED Strip / NeoPixel / WS2812
DC Barrel Jack / Power Connector
Enclosure / Box / Case

Browse all components

How It Works

This hardware-driven motion-activated lighting system operates entirely through analog and discrete circuitry, eliminating the need for a programmable microcontroller. At the heart of the system is a Passive Infrared (PIR) motion sensor, which detects changes in ambient infrared radiation caused by human or animal movement within its field of view. When motion is sensed, the PIR module outputs a control voltage signal from its data pin. Because this output signal has a relatively low current capacity, it is routed through a 10k resistor to the base terminal of a BC547 NPN bipolar junction transistor. The transistor functions as a solid-state electronic switch: when a positive voltage is applied to its base, it enters saturation mode, allowing current to flow freely from its collector to its emitter. This completes the control circuit for the electromechanical relay module (powered by a 12V supply). Once activated, the relay coil magnetizes its internal switch, closing the high-current contacts necessary to drive the external 12V LED strip. When the PIR sensor's internal timer expires and motion ceases, the base voltage on the BC547 drops to zero, cutting off transistor conduction, opening the relay, and automatically turning off the LED strip. The entire system is powered by a stable 12V DC adapter or battery connected via a standard DC socket, making it a reliable, standalone security and automation solution.

Why Build This

Design and implement a robust, microcontroller-free analog security lighting system suitable for undergraduate engineering demonstrations.

Gain practical experience in interfacing low-power sensor logic outputs with discrete transistor driver stages and higher-voltage electromechanical relays.

Understand power distribution and switching principles for 12V DC loads such as LED strips used in energy conservation and intrusion detection.

Real-World Application

Security systems, automatic hallway/staircase lighting, energy conservation in gardens and parking areas, and standalone motion alarms.

Skills You'll Learn

Discrete transistor switching

PIR sensor interfacing

Relay module operation

DC power distribution

Schematic reading and circuit wiring

Safety Precautions

Exercise caution when working with DC power supplies and relays connected to electrical circuits.

Technology Tags

PIR SENSOR

MOTION DETECTOR

LED

TRANSISTOR

BC547

RELAY

HOME AUTOMATION

INFRARED RADIATION

Frequently Asked Questions

Why is a BC547 transistor used between the PIR sensor and the relay?

The PIR sensor's output pin cannot supply enough electrical current to directly drive the coil of a 12V relay. The BC547 acts as a current amplifier and switch, allowing the low-power sensor signal to safely control the higher current required by the relay.

Can I program or change the time delay of the motion light?

Since this is an analog circuit without a microcontroller, you cannot change the timing via code. However, many standard PIR sensor modules feature onboard analog potentiometers that let you manually adjust the trigger sensitivity and the duration the light stays on.

What power supply should I use for this project?

You need a stable 12V DC power source, such as a 12V DC wall adapter or a compatible battery, capable of supplying enough current for both the relay module and the 12V LED strip combined.

Gallery

This page is part of Kitkraft's Project Hub — a curated collection of electronics & robotics projects gathered from the maker community to help students and hobbyists discover and learn to build. Kitkraft does not claim authorship of the original project, and makes no representation as to the accuracy, completeness or safety of third-party source material. The summary and "How It Works" explanation above are AI-generated, rewritten with reference to the original tutorial — not a reproduction of it. Full credit and a direct link to the original source are provided above. If you're the original creator and have a concern about how your work is represented here, please contact us and we'll address it promptly.

Kitkraft Project Hub — curated from the maker community, credited at the source.

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