Simple Doorbell with DC Backup Power Using UM66 IC

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A doorbell with DC Backup Power is a doorbell circuit that is even operational when the main power of a home, office or any building is cut off. This is highly preferable in building/home areas where there is electricity shortfall, load shedding, or other technical issues frequently seen. It works with both the AC supply of the mains and the DC supply of the backup battery.

Hardware Components

S.no	Component	Value	Qty
1.	Breadboard	–	1
2.	Connecting Wires	–	1
3.	Battery	9v	1
4.	IC	UM66	1
5.	PNP Transistor	2N4403	1
6.	NPN Transistor	2N4401	1
7.	Diode	1N914	1
8.	Zener Diode	3v	1
9.	Diode	1N4007	4
10.	Resistor	100, 220, 2.2k	1, 1, 1
11.	Capacitor	220uF, 0.1uF	1, 1
12.	Transformer	100mA/500mA, 6V	1
13.	Slider Switch	–	1
14.	Speaker	4 ohm	1

UM66 IC Pinout

2n4403 Pinout

2n4401 Pinout

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Circuit Diagram

Circuit Explanation

For the AC supply of the mains, a transformer is there to step down the main voltage of 2201V/110V to 6V. The variation of the output current of the transformer is from 100mA to 500mA. Four transistors 1N4007 arrangement is such that they make up a full-wave rectifier. A full-wave rectifier converts an AC voltage to pulsating DC voltage using both the positive and negative half-wave cycles of the AC power supply. The capacitor of 220µF, then, filters the rectified voltage coming from the bridge rectifier.

When the circuit needs backup or in case of mains power failure, the transistor 2N4403 shifts the circuit on the battery of 9V, automatically. Furthermore, a Zener diode, in this circuit, regulates the voltage, thus cutting it down to 3V. The rectified and filtered voltage, then, passes through 1N914 diode to the 3V Zener Diode. Cutting down the voltage to 3V is necessary for operating IC UM66. IC UM66 is responsible for generating melody for the doorbell. The IC UM66, thus, drives the 8Ω resistor that outputs the ringing of the bell.