Do More

If some intruder tries to open the door of your house, this circuit sounds an alarm to alert you against the attempted intrusion. The circuit (Fig. 1) uses readily available, low-cost components. For compactness, an alkaline 12V battery is used for powering the unit. Input DC supply is further regulated to a steady DC voltage of 5V by 3-pin regulator IC 7805 (IC2). Little Door Guard Circuit Diagram Fig. 1: Circuit of the door guard Assemble the unit on a general-purpose PCB as shown in Fig. 4 and mount the same on the door as shown in Fig. 3. Now mount a piece of mirror on the door frame such that it is exactly aligned with the unit. Pin configurations of IC UM3561 and transistors 2N5777 and BC547 are shown in Fig. 2.  Fig. 2: Pin configurations of UM3561 and transistors 2N5777 and BC547 Initially, when the door is closed, the infrared (IR) beam transmitted by IR LED1 is reflected (by the mirror) back to phototransistor 2N5777 (T1). The IR beam falling on phototransistor T1 rever...

This is a simple circuit of low-cost door knock alarm with timer. This is low-cost circuit uses the piezoelectric element of a piezobuzzer as the input sensor. The piezoelectric element plate is fixed at the centre of the door wing by using a cello tape. Apply a small quantity of adhesive at the edges between the plate and the door. Extend wires about 1-1.5 metres from the piezoelectric to the circuit. IC NE555 (IC1) is configured in monostable mode. Low-Cost Door KnocK Alarm With Timer Circuit Diagram: When it gets an input pulse its output goes high for a period set by VR1, resistor R5 and capacitor C3. IC UM66 (IC2) is used as a melody generator. When the door is knocked at, the piezo plate generates an input pulse, which is amplified by transistor T1. The amplified signal triggers the timer IC NE555 and its output pin 3 goes high to enable the melody generator. Music is heard from the speaker LS1. After the set time period, the melody sound stops. Assemble the circuit on a general-...

Here is electronic project of Simple Electronic Door Buzzer has a very simple function and is very easy to build.  This door buzzer circuit use a LF351 operational amplifier and other few common electronic components.  When the S1 push-button is depressed an initial positive voltage is placed on the C2 and the non-inverting terminal of the LF351 operational amplifier and the circuit will oscillate at a low frequency. Simple Electronic Door Buzzer Circuit Diagram: The used speaker for this project must have a impedance between 40 -80 ohms.  The door buzzer electronic circuit needs to be powered using a 9 volts DC power supply.