Home Automation Circuit Diagrams

Automatic Door Bell With Object Detection

At our homes, we all have a Automatic Door Bell.When a visitor arrives at our home, he looks for the doorbell switch and then rings it to let us know he’s there. What can be done if the person who came to our house couldn’t find the doorbell or if the person is too short to reach the doorbell? How will it be if we utilise an automatic doorbell that rings whenever someone enters our home? There aren’t any more annoyances. The individual who comes to our residence no longer needs to look for and press the doorbell. If we use an object detection circuit to install this automatic doorbell, the circuit will automatically identify the presence of a person and ring the doorbell.

Here’s how it typically works:

Object Detection:

  • The system is equipped with one or more sensors, such as cameras or motion detectors, that monitor the area around the entrance door. These sensors can detect the presence of people or objects within their field of view.

Image Processing:

  • If cameras are used, the system may employ image processing and computer vision algorithms to analyze the video feed in real-time. These algorithms can identify and classify objects or people based on their size, shape, or other visual features.

Object Recognition:

  • Once an object or person is detected, the system can recognize and categorize them. For example, it can distinguish between a person, a delivery package, a pet, or a vehicle.


  • When an object or person is detected and recognized, the system triggers the doorbell. This can be done using a traditional chime or a modern notification method like a smartphone app or a video intercom system. Homeowners or business owners receive an alert that someone or something is at the door.

Additional Features:

  • Depending on the sophistication of the system, it may offer additional features such as:

    • Two-way communication: Allowing you to communicate with the person at the door through an intercom system.
    • Remote access: The ability to view the live video feed or recorded footage remotely using a smartphone or computer.
    • Integration with smart home systems: The system may be integrated with other smart devices like smart locks, allowing you to remotely unlock the door or grant access to trusted individuals.
    • Alerts and notifications: You may receive alerts not only for visitors but also for specific events, such as package deliveries or unexpected visitors.

Recording and Storage:

  • Some systems may have the capability to record and store video footage, providing a record of all door activity.

Circuit Diagram of Automatic Door Bell Using Object Detection:

Automatic Door Bell

This circuit relies on a pair of ultrasonic transmitter and receiver modules to detect a person’s presence in front of the door and activate the doorbell accordingly.

Ultrasonic Transmitter and Its Frequency

The ultrasonic transmitter functions at around 40 kilohertz (KHz), continuously emitting ultrasonic waves. It’s crucial to moderate the power supply to limit the transmitter’s range to approximately one or two meters.

Why Transmitting Power Matters

The transmitting power’s range is critical to ensure effective detection without false triggering. Too short a range may lead to missed detections, while an overly wide range can cause the system to mistake distant objects for visitors, resulting in inconvenient alarms.

Ultrasonic Receiver Module and Sensitivity Adjustment

The ultrasonic receiver module operates at the same frequency as the transmitter, minimizing noise and false triggers. A 500K-ohm variable resistor (potentiometer) allows precise sensitivity adjustments for optimal performance.

Buzzer Circuit and Doorbell Integration

The circuit’s output is connected to a buzzer circuit, serving as the doorbell. The receiver, an LM324 IC, incorporates four op-amps, with three of them cascaded for our application. An opto-coupler is employed to isolate the circuit from the doorbell.

Final Assembly and Power Supply

Assemble the circuit on a compact PCB and affix it to your main door. For power, a 9V DC adapter with a filtered and regulated output is recommended. If such an adapter isn’t available, a 12V unregulated DC adapter with a 7809 voltage regulator can be used as an alternative power source.


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