Project Hub /Basic Analog & Power Electronics/Sequential, Timing & Pulse Circuits/12V Automatic Anchor Light Circuit Using 555 Timer and LDR

Intermediate

ANALOG / DISCRETE

Project Specific

3 – 6 Hours

Partial Kit

12V Automatic Anchor Light Circuit Using 555 Timer and LDR

An automatic 12V anchor light circuit built around an NE555 timer and an LDR ambient light sensor to automatically switch on at dusk and off at dawn.

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.

LDR Light Sensor Module Rs. 49.00
5V 1 Channel Relay Module Rs. 45.00
10pcs 5mm RED Diffused Light Emitting Diodes - LEDs Set Rs. 39.00
10pcs - 220 ohm 1/4 W Resistor Set Rs. 39.00
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 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: 555 Timer IC
Potentiometer / Trimpot
Capacitors
Custom PCB / PCB Fab
accumulator

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How It Works

This automatic anchor light circuit uses an LDR (Light Dependent Resistor) and an NE555 timer IC to monitor ambient light levels and control a 12V marine navigation light. The LDR acts as a variable resistor whose resistance changes inversely with light intensity: in bright sunlight, its resistance is very low, but as dusk falls and light levels drop, its resistance increases significantly. This change in resistance alters the voltage divider network connected to the input pins of the NE555 Timer IC (IC1). Working alongside a 470k potentiometer (VR1) and a 100uF capacitor (C1), the 555 timer evaluates the threshold voltage set by ambient conditions. When the ambient light falls below the user-adjusted threshold, the output of the NE555 changes state to trigger a 12V electromagnetic relay. The relay acts as an electrically operated heavy-duty switch, closing the circuit to supply power from the 12V DC power source or accumulator to the 10mm white LED. A current-limiting resistor (R2) protects the white LED from excessive current, ensuring it shines steadily throughout the night. At dawn, the increasing sunlight lowers the LDR resistance again, causing the NE555 to deactivate the relay and automatically turn off the anchor light, providing seamless hands-free operation.

Why Build This

Gain practical experience designing automated dusk-to-dawn lighting systems for marine and outdoor applications.

Learn how to integrate an analog light sensor (LDR) with an NE555 timer IC and an electromagnetic relay to drive high-power loads.

Build a functional, curriculum-aligned electronics project that solves a real-world navigational safety requirement for boats.

Real-World Application

Marine navigation, specifically for boats and commercial or recreational vessels requiring mandatory automatic anchor lights between sunset and sunrise.

Skills You'll Learn

Light sensor integration

Analog voltage divider design

Relay driving with ICs

Threshold detection

DC power management

Safety Precautions

Ensure proper waterproofing of the enclosure when mounting the electronics on a masthead in a marine environment.

Frequently Asked Questions

Can I use this circuit with a standard 9V battery instead of a 12V DC source?

No, the circuit is specifically designed around a 12V DC power source to properly actuate the 12V electromagnetic relay and drive the 10mm white LED.

What is the purpose of the 470k potentiometer (VR1)?

The potentiometer allows you to manually calibrate the exact light threshold at which the circuit triggers, ensuring the anchor light turns on precisely at dusk rather than too early or too late.

Why is an electromagnetic relay used instead of connecting the LED directly to the 555 timer?

The relay isolates the sensitive NE555 timer IC from higher power demands and allows the circuit to reliably switch heavier marine lighting loads using the 12V supply.

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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