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.
Circuit Diagram of Automatic Door Bell Using Object Detection:
This circuit operates using a pair of ultrasonic transmitter and receiver modules which are used to detect the person and then if the person is detected, the door bell is automatically turned ON when the person is in-front of the door.
The ultrasonic transmitter operates at a frequency of about 40 Kilo-Hertz. That means it continuously transmits the ultrasonic waves of about 40KHz. The power supply should be moderate such that the range of the transmitter is only about one or two meters.
If the transmitting power is less than one metre, it is possible that the person one metre away will not be identified. Furthermore, if the range is set to be very wide, it may result in false triggering, which means that objects far away from our door are mistaken for visitors and alarm rings. If the alarm goes off for every thing or person far away, this can be inconvenient for us. To avoid both concerns, the transmitting power is set as high as possible.
The ultrasonic receiver module receives the power at the same frequency as the transmitter, which eliminates noise and reduces false triggering. The 500K-ohm variable resistor arranged as a pot in the circuit can be used to adjust the receiver’s sensitivity. We can achieve the desired results by fine-tuning this. Our circuit’s output is sent to a buzzer circuit, which in our case serves as a doorbell. The receiver in this circuit is an IC LM324 with four op-amps on the inside. We’re only using four of the four op-amps and leaving the other one unused because it’s not needed in our situation. In a cascaded arrangement, the three op-amps are used.
An opto coupler is used at the output to avoid any interaction between our circuit and the door bell.
Assemble the circuit on a PCB as compactly as possible and then attach it to your main door. Thats it! You may provide a power supply using a 9V DC adapter with filtered and regulated output. If the 9V adapter with regulated output is not available, then we recommend you to use a 12V unregulated DC adapter with 7809 voltage regulator.