Want to protect our home or room from intruders?
This simple IR Burglar Alarm Circuit is our smart security buddy!
It uses invisible IR light to sense any movement or break in the beam.
The moment someone crosses the path, a loud buzzer alerts us instantly.
Easy to build, with low cost and perfect for beginners in electronics!
Circuit Working:
Parts List:
| Component Name | Value | Quantity |
|---|---|---|
| Resistors | 100Ω, 1/4 watt | 1 |
| 1k | 1 | |
| Variable Resistor Preset 50k | 1 | |
| Semiconductors | Transistor BC557 PNP | 1 |
| Phototransistor L14F1 | 1 | |
| Infrared LED (IR LED) | 1 | |
| Buzzer 3 to 12V DC | 1 | |
| Battery 9V | 1 |
IR LED sends invisible infrared light continuously.
The phototransistor L14F1 receives this IR light.
When any object or person blocks this light, transistor BC557 gets activated.
The buzzer turns ON and gives sound alarm.
When the IR beam is not blocked then the phototransistor keeps BC557 OFF and buzzer silent.
The 50k variable resistor VR1 controls the sensitivity of the circuit.
IR LED and resistor R1 100 ohm limits the current to safe value.
R2 1k resistor works as a load resistor for the phototransistor L14F1.
It helps convert light signal into voltage signal.
Formulas:
Below is the formula with calculation for IR Burglar Alarm Circuit:
Current through IR LED.
I = V / R
= (9V – 1.2V) / 100 ohm = 78 mA approx
This current is enough for IR transmission.
How to Build:
To build a IR Burglar Alarm Circuit following steps should be followed:
- Connect IR LED anode to 9V through R1 resistor.
- IR led cathode connect to GND.
- L14F1 collector connect to 9V through 1k R2 resistor.
- Connect emitter to base of transistor Q1 and one end of preset 50k VR1.
- Other end of VR1 connect to GND.
- Emitter of BC557 connect to +9V supply.
- Collector of BC557 connected to one terminal of buzzer.
- Other terminal of buzzer connect to GND.
- Connect 9V battery positive to positive of the circuit.
- And negative of 9V battery connect to GRN of the circuit.
Conclusion:
This IR Burglar Alarm Circuit is cheap and easy to make.
It can detect movement or interruption in IR beam.
By adjusting the VR1 the sensitivity can be changed.
It is useful for home, shop or lab security.