This electronic door buzzer circuit schematic 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 ampl
ifier and the circuit will oscillate at a low frequency. The used speaker for this project must have a impedance between 40 -80 ohms. The door buzzer electronic circuit need to be powered using a 9 volts DC power supply.