This project is for Laser Security Alarm Circuit using LDR and BC547 Transistors, as it uses LDR, two BC547 transistors, one diode and a buzzer.
When laser light breaks an alarm rings.
Additionally, this circuit is cheap and very easy to build and is good for door security, box security and drawer protection.
Circuit Working:
Parts List:
| Components | Values | Quantity |
|---|---|---|
| Resistors | 470k | 2 |
| LDR | 1 | |
| Semiconductors | Transistor BC547 | 2 |
| Diode 1N4148 | 1 | |
| Buzzer 9V Beeper | 1 | |
| Battery 9V | 1 |
Laser light always falls on LDR and when light falls on LDR the LDR resistance becomes low and then low resistance keeps Q1 and Q2 OFF.
So beeper stays OFF.
When someone blocks the laser light then LDR resistance becomes high and high resistance creates voltage drop across R1 and this voltage passes through diode D1 and R2 and drives the base of Q1.
Then Q1 turns ON and also turn ON Q2.
Then Q2 gives ground connection to buzzer and buzzer starts ringing and also finally, alarm continues until laser beam returns.
How to Build:
To build a Laser Security Alarm Circuit using LDR and BC547 Transistors following are the steps to follow:
- First, take all the parts as shown in circuit diagram.
- Next, battery positive goes to R1 and buzzer positive and R1 second pin goes to LDR top end and also LDR bottom goes to ground.
- After that, R1 and LDR junction goes to diode D1 anode and diode D1 cathode goes to R2 one end and R2 other end goes to ground.
- Now Q1 BC547 base connects to D1 and R2 node, Q1 emitter goes to ground and Q1 collector connects to buzzer negative.
- Then Q2 emitter goes to ground, Q2 collector joins with Q1 collector and buzzer negative and Q2 base goes to emitter of Q1
- Lastly, laser pointer must point to LDR directly.
Conclusion:
Overall, this Laser Security Alarm Circuit using LDR and BC547 Transistors is very easy project, as it works on simple LDR light change.
Also, two BC547 transistors amplify small change and activate beeper.
Moreover, this project is good project for beginners, with low cost and good for home security demonstration.