How to build melodious multi-tone bell

It is easier now to build a multi-tone bell giving melodious tones with the specially designed PCB design. Assembling becomes easier with this arrangement. Detailed steps are given below.

The specialty of the circuit

Uses IC 741 operational amplifier and just two transistors. The circuit can be energized with a 9V battery as current consumption is low as it draws current only when the switch is pressed and released immediately. 

Various tones are available by just rotating the R1 variable control.  Different tones are available with different settings of the rotor control R1. The output sound is obtained with an 8-ohm impedance loudspeaker. 

The amplifier stage uses just two transistors and just directly drives the speaker. In this circuit AC187/188 pair is shown as power amplifiers. If this pair is not available one can easily replace it with modern NPN/PNP silicon transistors like BC557/548. 

The circuit schematic is given here. 

Parts list

U1=741IC

Q1=BC557

Q2=BC548

R1=220K ohm mini variable resistor/preset

R2,R3, & R4=100K ohm Resistor

C1= 10MFD /12V electrolytic capacitor

C2=100MFD/12V electrolytic capacitor 

LS=8 ohms Loud speaker

Connect the Loudspeaker to points A B

PCB design

PCB copper track

One desires to use it as a doorbell, he/she can ingeniously add this in the doorbell system. Assembling is easier and all components are freely available in the market. Electronics enthusiasts, novice can try this circuit and assemble and boast oneself as a novel electronics project.