Project Hub /Basic Analog & Power Electronics/Sequential, Timing & Pulse Circuits/Simple Automatic Bathroom Light Circuit

Beginner

ANALOG / DISCRETE

Project Specific

3 – 6 Hours

Partial Kit

Simple Automatic Bathroom Light Circuit

An automatic bathroom light circuit that turns the light on when the door is opened using a reed switch and a small magnet.

Originally published on ElectronicsForU

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.

10pcs 5mm RED Diffused Light Emitting Diodes - LEDs Set Rs. 39.00
10pcs - 220 ohm 1/4 W Resistor Set Rs. 39.00
LM2596 Step Down DC-DC Buck Converter Rs. 99.00
Reed Switch 2×14mm Normally Open Magnetic Sensor Out of stock
5V 1 Channel Relay Module Rs. 45.00
400 Points Mini Solderless Prototype PCB Breadboard High Quality Rs. 89.00
MB102 Adjustable Breadboard Power Supply Module (3.3V & 5V) for Arduino & Raspberry Pi Rs. 139.00
Jumper Wire 10 Pin Male To Male 20cm Rs. 45.00
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: Voltage Regulator IC (7805 / LM317 / 1117)
Op-Amp IC (LM358 / LM741 / TL072)
Logic ICs (74xx / 40xx)
Diodes (1N4007 / 1N4148 / Schottky / Zener)
Transistors (BC547 / 2N2222 / TIP / MOSFET)
Screws / Nuts / Standoffs / Hardware
Capacitors

Browse all components

How It Works

The Simple Automatic Bathroom Light Circuit uses a step-down transformer (X1) to reduce 230V AC mains electricity down to a safer 9V level. A 1A bridge rectifier (BR1) converts this AC voltage into pulsating DC, which is then smoothed by a capacitor (C1) and regulated by an LM7805 5V voltage regulator (IC1) to supply steady power to the control electronics. The core sensing mechanism relies on a reed switch and a small magnet mounted on the bathroom door. When the door opens, the magnetic field changes, triggering the circuit. An op-amp 741 (IC2) processes the signal, and a 4017 decade counter (IC3) helps sequence the logic. This drives a transistor pair consisting of a BC557 PNP transistor (T1) and a 2N2219 NPN transistor (T2), which together amplify the signal enough to switch a 5V single changeover relay (RL1). When the relay activates, it completes the circuit to turn on the bathroom light, while a 5mm LED (LED1) provides a visual indicator that the system is operating. Resistors like R1, R2, R3, and R4 control the electrical current flowing through the various parts, ensuring safe operation.

Why Build This

Build a fun automatic light for your room that turns on by itself whenever the door opens.

Learn how magnets and tiny switches can work together to control electricity.

Help save energy at home by making sure lights never accidentally stay left on.

Real-World Application

Automated home lighting for bathrooms, restrooms, and storage rooms to save electricity and improve convenience.

Skills You'll Learn

Voltage regulation

Rectification and AC-to-DC conversion

Magnetic sensing with reed switches

Transistor switching

Relay operation

Counter logic circuits

Safety Precautions

Be sure to consult a qualified electrician if you're not comfortable with electrical work or if you need help with installation. Safety should always be your top priority when working with 230V AC mains electricity.

Frequently Asked Questions

How does the circuit know when the door opens?

It uses a reed switch and a small magnet. When the door moves, the magnet moves away from the reed switch, which changes the electrical signal to trigger the light.

Do I need to plug this into a normal wall outlet?

Yes, the project uses a step-down transformer to connect to 230V AC mains power, which means you must be very careful and get help from an adult or qualified electrician.

What is the relay used for?

The 5V relay acts like an automatic electrical switch that allows the low-power electronic circuit to control the higher-power bathroom light safely.

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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