In this tutorial, we are making a project of a loud door security burglar alarm. This circuit will activate an alarm that is louder than usual alarms when the door is opened and once the alarm activates it will continue ringing until the authorized person deactivates it by closing the door. It can be very useful to detect intrusions or any unauthorized entry.
This circuit is using two ICs, one is a 555 timer IC and the other is a siren sound generator IC UM3561. The UM3651 IC is wired to produce only one sound. A normally closed Reed switch is used in this circuit for sensing purposes. A small piece of the magnet should be attached at the other part of the door and in front of the reed switch to make it open.
Hardware Components
| S.no | Components | Value | Quantity |
|---|---|---|---|
| 1. | Input Supply DC | 6-12V | 1 |
| 2. | Switch | Reed | 1 |
| 3. | Resistor | 10KΩ, 470Ω, 180KΩ, 5.6Ω/1W, 120Ω, 2MΩR | 1, 1, 1, 1, 1,1 |
| 4. | Capacitor | 100µF (C x), 0.1µF | 1, 1 |
| 5. | Speaker | 8Ω/2-5W | 1 |
| 6. | Zener diode | 3.3V | 1 |
| 7. | IC | NE555, UM3651 | 1, 1 |
| 8. | Transistor | TIP125 | 1 |
Circuit Diagram
Working Explanation
The working of this circuit is quite simple, when any burglar, intruder, or an unauthorized person will open the door, the distance between the reed switch and the magnet will increase. Because of this the reed switch will go from normally open to normally closed and triggers the 555 timer IC. The 555 timer IC’s output will become high and it activates the UM3561 alarm circuit. We are using the time delay mode of the 555 timer IC so once it is activated it will not deactivate until the preset time period is completed no matter when the door is closed or the reed switch becomes normally open. Preset time is set by the variable resistor. You can further increase it by increasing the value of the capacitor Cx.
