A laser burglar alarm is a security purpose alarm circuit that senses even a small interruption in its environment. It’s sensitive with a long range of detection whose alarm once activated can last for up to 1 minute.
Hardware Components
The following components are required to make Laser Burglar Alarm Circuit
| S.no | Component | Value | Qty |
|---|---|---|---|
| 1. | Transistor | 2N4401, 2N4403, 2N3904, 2N3906 | 1 |
| 2. | IC | UM3561 | 1 |
| 3. | Darlington Transistor | TIP120 | 1 |
| 4. | Laser Pointer | – | 1 |
| 5. | LDR | – | 1 |
| 6. | Battery | 9V-12V | 1 |
| 7. | Zener Diode | 3.3V | 1 |
| 8. | Speaker | 8Ω | 1 |
| 9. | Resistors | 120Ω, 470Ω, 1K, 47K, 180K, 470K | 1,1,2,1,1,1 |
| 10. | Variable resistor | 1KΩ | 1 |
| 11. | Electrolytic capacitor | 470µF | 1 |
UM3561 Pinout
For a detailed description of pinout, dimension features, and specifications download the datasheet of UM3561
TIP120 Pinout
For a detailed description of pinout, dimension features, and specifications download the datasheet of TIP120
Laser Burglar Alarm Circuit
Working Explanation
This circuit includes a laser beam and an LDR to detect that beam. The LDR connected with the circuit is to be placed inside a box or a dark place where no light can enter. Then, punch a hole into that box and set the laser beam such that only the light from the laser can enter through it. After this setup, adjust the 1KΩ variable resistor to set the sensitivity of the project.
Now, when there is an intruder that cuts the laser beam falling onto the LDR, the system is activated. Thus, the resistance of LDR increases signaling to the transistor 2N4401 to start the operation. The trigger of transistor 2N4401 amplifies the signal as well as activated the other transistor in the circuit. Moreover, transistor 2N3906 is responsible for switching the IC UM3561 input pin HIGH. Thus, the IC performs its function and then drives the 8Ω speaker. Therefore, the alarm sets ON producing a loud alarm tone.
Application
- Security system
- Long-distance proximity sensor
