Electronic door buzzer circuit schematic

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 amplifier 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  .