Calling Bell circuit design

Project-01. Calling Bell circuit diagram.

Description

The project provides the schematic and the parts list needed to construct a musical door bell. The door bell is operated at 1.5v-3.0v as well as with an musical IC (UM66) to make the circuit. As a modified circuit it is successfully operated in ac supply as well as in dc supply when ac supply will be turned off as we required.    

The circuit has been built using the basic characteristics of transistors. A musical IC UM66 is used to generate musical tone which is further amplified using a transistor. The charging time of the capacitor can be controlled by the variable resistor of 100KΩ. For AC power supply, two 470KΩ resistors is used along with a bipolar capacitor of 250V in parallel. Then a bridge network is connected to convert AC to DC.  Zener diode in parallel makes the voltage constant. This constant voltage ensures the power source for the circuit. At the same time it is connected with the base of the PNP transistor. When AC supply is on the E-B is reverse biased, so no current will flow through the Base to Collector. In this way the battery source is switched off. But if the AC power is off the transistor becomes forward biased. So the current will conduct through base to collector. In this way, the power source for the circuit is automatically switched to the available power source.


Circuit Description:
There we have used a 1.0µF capacitor and two 470k resistors by replacing transformer. Then a bridge rectifier is used to supply the input voltage to the main door bell circuit. The output voltage of our supply is 4v which is required to operate the door bell. At the modified section we have used a p-n-p transistor (BC557AP),a resistor(500Ω) and two diodes(1N4001GP) which will operate the circuit in dc supply in the absence of ac supply as we predicted. 

Apparatus:

—  IC                         (UM66)                                      1pc

—  Speaker                (8 Ω  0.5W)                                1pc

—  Diode                    1N4007)                                     5pcs

                              1N4732 (Vz = 4.70V)                  1pc

—  Capacitor              1µF (bipolar) 250V                     1pc

                                   220µF                                         2pcs

—  Resistors               470KΩ                                       2pcs

                                    100 Ω                                        1pc

                                    4.7K Ω                                      1pc

                                    500 Ω                                        1pc

—  Transistor              BC 557                                      1pc

                                    BC548                                       2pcs