automatic doorbell system
Automation Cool homemade utility Gadgets / circuit projects ECE engineering projects PIR Proximity sensor/IR obstacle sensor Security Based Automation Sensor based

Automatic doorbell system with auto-detection | 2 circuits

Hello Engineers, Its an automation world. Everything is automated. So why not doorbell? Today, in this tutorial I am going to discuss a circuit that is an automatic doorbell system with auto-detection. This circuit detects automatically if someone is standing at the door and turns the bell circuit on by giving it power. So, let’s get started with our topic automatic doorbell system or automatic doorbell alarm system with object detection.

1st method using PIR in an enclosed box Automatic doorbell system

In the 1st method, a PIR is used to detect the object or person. The PIR sensor is enclosed and surrounded in a box such as a cylindrical shape to prevent surrounding disturbance. To understand basic PIR working click here to this article The PIR is placed upside down and when detects any movement under it, then provides TTL output to further control circuitry.

The circuit diagram

Automatic doorbell system


  • PIR sensor ( difficulty finding PIR in local shops? buy 5pcs from amazon @ $ 5 )
  • Relay12v
  • TIP122 transistor
  • R1 680 ohm
  • PCB

In the circuit above PIR is used to detect the objects. Its enclosed in a box-type structure to sense only movements below it.

PIR sensors do not emit any energy or rays, instead, it detects the infrared radiations emitted by or reflected by surrounding objects. All living or non-living beings having a temperature above absolute 0 emits heat in the form of radiation. A PIR sensor is used for detection of motion by Objects, human beings, animals, etc any kind of movement by any entity.

A PIR requires an input voltage of 3.5v -5v dc at the VCC pin to operate and it gives a TTL( Transistor-Transistor Logic) output directly to the microcontroller’s pin or to the relay driver transistor when it senses motion in its proximity.

Once the transistor gets supply, it turns the relay that connects the BELL to AC domestic supply. This is how this circuitry method works. I prefer to use this PIR method as it’s a more effective and easy setup.

2nd method by using IR Obstacle sensor

automatic doorbell system

The main component is the IR obstacle sensor or IR proximity sensor that does the main work of sense. It’s a type of active infrared sensor which has an infrared emitter as well as an IR detector. So, the working of this obstacle sensor is very simple and easy to understand.

After the sensor is given input 3.3 to 5v dc, the IR emitter LED starts emitting IR light continuously. When an obstacle comes, the IR light is reflected back by it and detected by the IR photodiode. The sensor then provides TTL(Transistor-Transistor Logic) output to the further control circuits. The detection range of the sensor can be set by the preset present over the sensor’s PCB.

The circuit and it’s working


  • IR Obstacle sensor
  • Q1 TIP122 -1pc
  • D1 1N4007 – 1pc
  • RL1 Relay 12v – 1pc
  • R1 680ohms-1K
  • PCB – 1pc

In the circuit shown above, the sensor senses the object or any obstacle with the help of IR Rays.

Sender LED transmits the IR light and when an obstacle comes, it’s reflected back and sensed by the IR receiver. The sensor then provides the TTL output to the connected TIP122 that makes the relay turn ON. The relay after turning ON connects the doorbell to the Domestic AC supply.

Any normal doorbell can be used with this circuit. There are two installation method can be used to install the sensor so that it would be easier to detect the person. This can be chosen according to the vantage of the user.

I prefer to install the setup using the PIR circuit according to the 1st method as it would be suitable for people with all heights. Just enclose it in a box to prevent the surrounding disturbances.

Content Protection by
Aabhishek Sharma is a Computer Science Engineer and a Digital Marketing Trainer and Consultant. Aabhishek Sharma also loves working on Electronics Projects and working with microcontrollers and Designing Home automation Gadgets.

8 Replies to “Automatic doorbell system with auto-detection | 2 circuits

Leave a Reply

Your email address will not be published. Required fields are marked *