IR based Security Alarm Circuit using NE555 timer IC

IR Security Alarm Circuit

Welcome to another episode, in this episode, we will learn about IR based security alarm circuit using a NE555 timer IC. This is an important electronics projects for beginners. Today we will also learn,

  • How to make security alarm circuit
  • Practically, we will learn this circuit working principle
  • We will learn about NE555 timer IC
  • Also, I will design schematic and PCB design Gerber files.

This is an awesome electronics project idea and useful circuit for real world application. You can use this circuit a lot of place like Office, House, Bedroom, street, Store room etc. This is really useful circuit for security system.  If you’re beginner in electronic world and if you want to make it for your daily life, this tutorial will be helpful for you.

Appliance which are requirement for this project

To make this project, we need some components. Let’s collect materials below the list.

For transmit and Receive Infrared Ray

  1. IR LED
  2. Photo Diode
  3. Resistor 270 Ohm, 3.3K


For A stable Multi-vibrator timer circuit

  1. IC NE555
  2. Resistor 10K, 330 Ohm
  3. Capacitor 47uF
  4. LED
  5. Transistor BC547
  6. Battery or power supply
  7. Potentiometer 10K
  8. Some connection Wire


≡ IC (NE555) Pinout

The timer IC (NE555) is an integrated circuit that used in variety of timer, delay count and pulse generation etc. Here the pin diagram of this IC.

NE555 timer IC


≡ IR Security Alarm NE555 Connection Diagram 

The circuit connection diagram too easy. You can make this circuit to see below the schematic diagram very easily. Here see below the schematic diagram of the circuit.

IR Security Alarm Circuit


≡ Circuit Connection

The positive terminal and the negative terminal of the IR transmitter are connected to the ground through a 270-ohm resistor from 5volts and the negative terminal of the IR receiver (Photo Diode) is connected to the positive, and the positive terminal is connected to the ground by a 3.3K ohms resistor of the transistor base.

Here an IR transmitter and receiver are connected being close together (that’s mean face to face connection). On the other hand, the transistor (BC547) emitter is connected with GND and the collector is connected with NE555 IC pin number 4.

The IC NE555 pin 8 and 1 are connected VCC and GND. Here the pin number 3 is an output pin that connected with a resistor and a LED in GND. Also, a buzzer is connected with pin 3.


What is an Infrared LED?

Infrared LED (IR LED) is an LED that emits infrared light. That means it reduces the infrared frequency that’s invisible to us. The wavelength of this frequency is 700nm to 1mm. The IR LED looks like a normal led. It takes a maximum current of 20mA and the maximum voltage is 3 volts.


What is a Photodiode?

A Photodiode is a semiconductor device that converts the light into current based on the mode of operation of the device.


≡ Working Principle of the circuit

When an object is placed in middle of both, the radiation from the transmitter reaches the receiver due to the reflection. And the photodiode converted the reflection into current. Then we set the voltage on the transistor base terminal that we collected from photodiode. Here the transistor acts as a switch and the collector terminal connected the Reset pin to ground, when the IR rays received by photodiode.

When the reset pin of timer IC will receive 0 volts from the transistor, it reset all the process of timer IC. Though we set the IR led and photodiode on face to face. As a result, the photodiode will generate a voltage continuously and the reset pin will always low or 0 volts. So, we see the output pin is low because the IC resetting continuously. But if we placed an object in middle of IR transmitter and receiver the photodiode stopped to convert infrared ray into current. As a result, the transistor will go off and the reset pin collect positive voltage from the transistor collector terminal and the timer IC will go start timing operation and the output will goes HIGH.

The timer IC output is depending on the timer resistor, Potentiometer or variable resistor and timer capacitor. By changing the value of resistor, capacitor and potentiometer we can get different level output.

Download Circuit Diagram and PCB Click

More Mini Electronics Project click

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