Monday, October 21, 2013

Automatic Doorbell with Object Detection Circuit

Automatic Doorbell with Object Detection Circuit


The circuit operates using a pair of ultrasonic transmitter and receiver modules which are used to detect the person. When the person is detected (the person is in the front door), the doorbell is automatically turned ON.


Figure 1  Automatic Door Bell with Object Detection Circuit Diagram

The ultrasonic transmitter operates at a frequency of about 40 kHz, which means it continuously transmits the ultrasonic waves of about 40 kHz. The power supplied 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 meter, then there is a possibility that the person who is one meter away will not be detected. Likewise, if the range is set higher, then it may lead to false trigerring which means that objects from afar maybe considered as visitors triggering the circuit. So to avoid these problems, the transmitting power is kept to an optimum level.
The ultrasonic receiver module receives the power with the frequency the same as that of the transmitter so that the noise will be eliminated and minimized false triggering. The sensitivity of the receiver can be tuned by using a 500 kilo-ohm variable resistor arranged as a pot in the circuit. By tuning this properly, we can achieve the desired results. The buzzer circuit is the output load which acts a doorbell in the case. The receiver circuit uses the integrated circuit LM324 which has 4 operational amplifier internally. Out of the four, three operational amplifiers only are being utilized. The three op-amps are arranged in cascade to provide high gain as well as noise free output.
An optocoupler is used at the output to avoid any interaction between the circuit and the doorbell.
Assemble the circuit on a PCB as compactly as possible and then attach it to the main door. You may provide a power supply using a 9 VDC adapter with filtered and regulated output. If the 9 V adapter with regulated output is not available, then we recommend you to use a 12 V unregulated DC adapter with 7809 voltage regulator.

Electronics  lab   ,     Created by Muhammad Irfan Electronics  lab   ,     Created by Muhammad Irfan


  1. Good concept. But I think this circuit diagram is taken from ElectronicsHub.Org Blog. In that blog, it is well explained. If anybody interested, visit

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