Automatic doorbell with object detection

Every house has a doorbell. When a visitor arrives at a home, he looks for the doorbell switch and rings it to let us know his presence. What if a person coming to your home cannot find the doorbell, or the person is too short to reach the doorbell? The following object detection circuit is installed for reference. The circuit will automatically sense the presence of a person and ring the doorbell. This circuit works using a pair of ultrasonic transmitter and receiver modules for detecting people, then if a person is detected, the doorbell will automatically open when the person is in front of the door. The operating frequency of the ultrasonic transmitter is approximately 40KMHz. This means that it continuously emits ultrasonic waves of about 40KHz. Adjust the power supply so that the range of the transmitter is only about one or two meters. The ultrasonic receiving module receives power at the same frequency as the transmitter, thereby eliminating noise and reducing false triggers. The sensitivity of the receiver can be adjusted by using a 500K ohm variable resistor arranged as a potentiometer in the circuit. By adjusting it appropriately, we can achieve the desired results. The output of our circuit is fed to a buzzer circuit which acts as a doorbell in our case. The receiver in this circuit uses IC LM324, which has four operational amplifiers inside. Out of the four op-amps, we use only four of them and leave the other one unused because not much is needed in our case. Three op amps are used in cascade to provide high gain and noise free output. Use an optocoupler on the output to avoid any interaction between our circuit and the doorbell. Assemble the circuit as compactly as possible on the PCB and connect it to the main door. That’s all! You can provide power using a 9V DC adapter with filtered and regulated output. If a 9V adapter with a regulated output is not available, then we recommend you use a 12V unregulated DC adapter with a 7809 voltage regulator.