Simple and Affordable Door Alarm Circuit Using CMOS IC
Security is a top priority for any home or office. If you're looking for a low-cost and efficient door alarm, this CMOS IC-based circuit is a perfect solution. It operates with a universal AC-DC power supply and produces a distinct pip-pip-pip sound when a door or window is opened.
How This Door Alarm Works
This circuit is designed not to mimic a loud siren but rather to act as a subtle yet effective security alert, signaling that someone has entered.
Key Components & Their Functions:
🔹 IC1a (Oscillator): Generates a fast-frequency tone.
🔹 IC1b (Oscillator): Produces a slow-frequency tone.
🔹 IC1c (Mixer): Combines both oscillators to create a pulsating alarm sound.
🔹 IC1d (Timer): Ensures that the alarm continues for 20-30 beeps even after the door is closed.
🔹 VR1 (Variable Resistor): Adjusts the frequency of the sound.
🔹 S1 (Piezo Buzzer): Emits the alert sound when triggered.
🔹 Alternative Option: S1 can be replaced with an LED (with a 1KΩ resistor) for a visual alert instead of an audible one.
Circuit Operation
1️⃣ When the door is closed, the switch remains in its normal state, and the circuit is idle.
2️⃣ When the door is opened, the switch activates, and the circuit triggers the alarm sound.
3️⃣ The alarm continues for 20-30 beeps even after the door is closed, ensuring enhanced security.
4️⃣ If needed, R1 and D1 can be omitted, and R2 can be adjusted to modify the alarm tone.
How to Set Up the Door Switch
🔹 A reed switch can be converted into a normally closed switch, ensuring activation when the door opens.
🔹 Micro-switches or other types of contact switches can also be used for reliability.
🔹 Be careful when soldering reed switches, as they can be fragile.
Conclusion
This simple door alarm circuit using a CMOS IC is an effective DIY security solution. Whether for home or office, this system offers a low-cost, customizable, and efficient way to secure entry points.
🔧 Try building this alarm today for an extra layer of protection! 🔧
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