Warning system door open alarm circuit | uses 555 timer and LDR.

How are you all? I hope you are well. By the grace of God, I am also well. Today I will share with you a door-open alarm circuit, which will alert us as soon as the door is opened.

Edited with Canva.

This circuit uses a 555 timer IC and an LDR sensor that can sense the light when the door is opened and immediately sound the alarm. It can be used not only for the refrigerator door but also for the door, window, cabinet, cupboard or chest. This very simple circuit I have drawn with my own hands and have beautifully illustrated step by step with coloured pens.

Parts used and their functions

555 Timer IC.

Edited with Canva.

Used for timing control and signal generation.

LDR: Light Dependent Resistor.

Changes resistance to generate a signal when the light decreases or increases.

Diode 1N4148.

Protects the circuit from reverse current.

Resistor: 10k, 2M, 1M.

Used for voltage division, timing and signal control.

Capacitor 1µF, 100nF

Works in charge holding and timing configuration.

Buzzer.

Sounds when the door is opened.

Battery.

A 3.7V to 5V battery is used to supply power to the circuit.

Step 1: Gathering the necessary equipment.

Before starting my drawing work, I collected some necessary equipment. These included coloured pens, pencils, scales and an art page. With these materials, I drew the circuit diagram step by step.

Step 2: Dual 555 Timer IC Connection.

In this step, I used two 555 timer ICs. Pins 4 and 8 of IC-1 and IC-2 are connected together to provide a +3.7V to 5V power line. Pin 1 of the two ICs is connected to the ground line. The main timing and output control of the circuit will be done through these two ICs.

Step 3: LDR and capacitor connection.

In this step, I have used an LDR photoresistor whose main function is to detect the presence of light when the door is opened. When the light falls on the door, the resistance of the LDR decreases, and then a signal is sent to the trigger pin of the 555 Timer IC-1. In addition, a D1 diode and a 1 µF capacitor have been used to process the signal properly.

Step 4: Signal trigger and output alarm.

In this step, I have connected a buzzer to the output line of IC-2, which gives a warning by making a sound as soon as the door is opened. I have used R3 and C2 to control the time so that the alarm remains on for a while. The protection of the output has been ensured through the R4 resistance. Finally, I have written the username and community name neatly.

Conclusion.

I have made the entire project step by step by hand. Here a door open alarm has been made using two 555 timer ICs, which gives a sound warning as soon as the door is opened. In this circuit I have used an LDR and other components which have made it effective and easy to use. It can be used for the security of any door, not just a fridge.

List of used parts.

Components	Value	Qty
IC	IC1: 555 Timer, IC2: 555 Timer	1, 1
Polar Capacitor	C1: 1µF 25V	1
Non-Polar Capacitor	C2: 100nF	1
Resistor	R1: 10KΩ 1W, R2: LDR, R3: 2.2MΩ 1W, R4: 1MΩ 1W	4 incl. LDR
Diode	D1: 1N4148	1
Buzzer	Piezo Type DC	1

🟩 Thank you for reading my post and giving your valuable time. Stay well and stay healthy. God bless you. 🟩

Photography Details	📱 Device: Walton Xanon90	📍 Location: Narayanganj, Bangladesh	📷 Captured By: @imranhassan