It has become necessary to verify the identity of a person or visitor before opening the door as he may be a burglar . This switchless bell circuit will help you to [[wysiwyg_imageupload::]]identify who is standing at the door as it that activates through the puff of your breath or with a clap. Only those who know the place of secret bell would puff out before the hole of the switch box and now door can be opened without any fear. Interestingly, this circuit does not use a microcontroller but only a BC547 transistor, a microphone, buzzer, switch, LED, a few resistances and capacitances.This Transistor based secret bell circuit is based on the property of the transistor to amplify weak signals. In this, the condenser mic fitted inside a hole of a switch box will trigger the bell on detecting the change in air pressure as you clap or puff your breath.
Many times it happen when somebody comes home in night and press the door bell, We search for the porch light switch. To identify that the visitor who as press the door bell is known or unknown person before opening the door. This circuit will help you to solve the problem. When a visitor press the doorbell switch it will automatically on the porch light after sometime so that when you reach near the door you don’t have to search for light switch. This circuit will automatically off the light after some time. This circuit also has the facility to on the porch light from inside the house. In day time you can off the light with the help of switch S3. Doorbell cum light has inbuilt doorbell so you do not require to purchase a door bell.