In most of the homes the door bells are conventional ding-dong type. Most of us don’t like its sound. Due to mechanical moving parts with spring mechanism its long term durability is questionable. I had also one such door bell in my home. After a period of time its performance deteriorates and one time it becomes completely intolerable because of its noisy irritating sound.
The new types of door bells available in market are bird sound door bell. They are costly. and even I didn’t like it because of its high frequency and high volume sound output.
So the idea came into my mind that why not to build a very simple door bell with few components that gives nice melodious output and that is at the less cost also. So I build this door bell with all the items available in home. Let us see how I have made it.
First collect the required components
· Transformer – 230 V to 18 V@500 mA
· Diode bridge or 4 diodes – 1N4004
· Capacitors – 1000 µF, 0.1 µF
· Resistors – 560Ω
· Voltage regulator ICs – LM7805, LM7812
· Relay – 12 V 1 C/O
· Transistor – 2N2222A
· 8Ω speaker
· Melody generator IC UM66
Now build the circuit on general purpose PCB. (See the circuit diagram tab for the doorbell circuit)
· 230 VAC is applied to primary of transformer with bell switch in between as shown
· The secondary of transformer is connected to AC input terminals of diode bridge
· A 1000 µF capacitor is connected across rectified output terminals of diode bridge
· This output is given as input to both voltage regulator chips 7812 and 7805
· The output of 7812 IC drives relay coil directly. A filter capacitor of 0.1 µF is connected across it.
· The output of 7805 is given to common terminal of relay
· The second normally open terminal of relay is connected to input of UM66 through voltage divider network made up of resistors R1 and R2
· The output of UM66 drives 8Ω speaker through NPN type transistor Q1
· When bell switch is pressed and hold for some time (2-3 sec) the AC supply is given to primary of transformer
· The diode bridge rectifies AC supply available from secondary. Capacitor C1 filters it out and finally 7812 will generate 12 V and 7805 will generate 5 V
· As relay gets 12 V, it energise and switches ON
· So common terminal gets connected to normally open terminal and 5 V supply is given to UM66 through voltage divider. Due to same values of R1 and R2 2.5 V is given to UM66
· UM66 generates musical sound output that is amplified by Q1 so that musical output is audible through speaker
Here is the photograph of the circuit that is completely housed in a plastic box. The plastic box is hanged on the wall at the place where wire connections for door bell are given. The transformer primary inputs are taken out of box and connected with these wires as shown in photograph given below.
Now when external door bell switch is pressed and hold for 2-3 seconds a musical – melody sound is produced from bell.