Project Hub /Basic Analog & Power Electronics/Sequential, Timing & Pulse Circuits/DIY Kitchen Security Alarm Circuit

Beginner

ANALOG / DISCRETE

₹500 – ₹1,500

3 – 6 Hours

Partial Kit

DIY Kitchen Security Alarm Circuit

This project guides you through creating an LPG leakage and smoke detector using an MQ2 gas sensor and standard analog integrated circuits.

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
DC Motor Plastic Fan Blade Rs. 19.00
5V 1 Channel Relay Module Rs. 45.00
MQ-2 Smoke Sensor Detector Module Rs. 129.00
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)
LM35 / Analog Temp Sensor
555 Timer IC
Transistors (BC547 / 2N2222 / TIP / MOSFET)
Diodes (1N4007 / 1N4148 / Schottky / Zener)
Capacitors
Header Pins / Terminals / Connectors
9V Battery + Snap

Browse all components

How It Works

The DIY Kitchen Security Alarm Circuit relies on a combination of power regulation, analog signal conditioning, and timing control to detect LPG leaks or smoke. Power is supplied by stepping down 230V AC mains voltage using a transformer connected to a 1A bridge rectifier (BR1) and smoothed by filter capacitors (C1 and C2). The LM7805 voltage regulator (IC1) steps this down further to a steady 5V DC rail to power the logic and sensors. The core detection mechanism uses an MQ2 gas sensor (Sensor1), which changes its internal resistance in the presence of combustible gases or smoke. An LM358 operational amplifier (IC2) acts as a comparator, monitoring the analog output of the gas sensor against a reference threshold. When gas concentration exceeds the preset level, the op-amp output goes high, triggering the NE555 timer (IC3) configured in a monostable or timing configuration. The output of the timer drives a pair of 2N2219 NPN transistors (T1 and T2) connected in a Darlington or cascading configuration to supply sufficient current to actuate the 5V SPDT relay (RL1). Simultaneously, a 5mm LED (LED1) illuminates to provide visual indication. The relay switches the high-voltage 230V AC exhaust fan on to clear the air, while a diode (D1) protects the low-voltage circuitry from inductive kickback generated by the relay coil during switching.

Why Build This

Design and implement a standalone analog gas-detection safety system for residential or commercial kitchens using classic integrated circuits.

Gain practical experience interfacing chemical gas sensors with operational amplifiers and timing integrated circuits without relying on microcontrollers.

Learn how low-voltage control circuitry safely interfaces with high-voltage AC mains components like transformers and exhaust fans using electromechanical relays.

Real-World Application

Kitchen safety systems, automated exhaust activation during gas leaks, and early fire warning alarms in residential or commercial kitchens.

Skills You'll Learn

DC power supply design

AC mains step-down transformation

analog voltage comparison using operational amplifiers

sensor signal conditioning

timer circuit configuration

relay driver design with transistor switches

Safety Precautions

Exercise caution when working with 230V AC mains voltage used for the transformer and exhaust fan to prevent electrical shock.

Technology Tags

MQ2 GAS SENSOR

LM358

NE555

GAS LEAKAGE DETECTOR

SMOKE DETECTOR

ANALOG CIRCUIT

ALARM CIRCUIT

RELAY

Frequently Asked Questions

Do I need to write any code or program a microcontroller for this project?

No, this is a purely analog and discrete hardware project, meaning no software or programming is required.

How does the MQ2 sensor know when to trigger the alarm?

The MQ2 gas sensor changes its electrical resistance when exposed to smoke or LPG, which alters the voltage input to the LM358 op-amp comparator. Once this voltage crosses the set threshold, the circuit activates.

Can I connect the exhaust fan directly to the low-voltage DC circuit?

No, the exhaust fan operates on 230V AC mains voltage and is isolated from the low-voltage DC circuit, being switched safely via the 5V SPDT relay.

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.

PRJ-00797