Introduction
For the sake of security, The presence of any people or object in a certain region/place is detected using a light fence circuit. Using an LDR and an Op-amp, the circuit is relatively simple to create. The alarm sound emitted by the buzzer is loud enough to identify the presence of a human, vehicle, or item in this portable circuit, which runs on a frequently accessible battery. So, in this tutorial, we are going to make a “Light Fence circuit”.
This is a simple Light Fence circuit that may be used for security. By installing a light fence at the doorway or entry door, we can be warned before someone knocks. As a light source, use a white LED biassed with a 220ohms 3Volt battery.
Hardware Required
| S.no | Component | Value | Qty |
|---|---|---|---|
| 1. | IC | 4069 | 1 |
| 2. | LDR | – | 1 |
| 3. | SPST Relay | 9v | 1 |
| 4. | Light source white LED | – | 1 |
| 5. | Transistor | 2N4401 | 1 |
| 6. | Diode | 1N4001 | 1 |
| 7. | Capacitor | 1uF/20V, 100nF | 1, 1 |
| 8. | Resistor | 100KΩ, 10KΩ | 1, 2 |
| 9. | Battery | 9v | 1 |
Circuit Diagram
Working Explanation
The circuit operates when the LDR senses any activity, according to the circuit diagram. When the opamp ic is activated and the transistor conducts, the LED begins to glow, and the buzzer sounds. As a result, anytime a person or item enters a restricted area, the LDR detects his shadows and the circuit activates the alarm.
Application and Uses
A light fence circuit is used to identify any object or person in a defined zone. Thus it can be used in:
- Security alarm circuits.
- Intruder or burglar alarms.
