In this tutorial, we are making a project of mains power come back alarm. Mains power goes off for various reasons some times because of technical issues. But in some countries due to load shedding, it goes off frequently every day to overcome this issue people use either an uninterruptible power supply UPS or a generator to have the electricity until the mains power comes back. In these cases a mains power comes back alarm always comes in handy, this will alert you every time whenever the mains power is back through a melodious alarm.
There are two ICs used in this circuit. the first one is a timer IC i.e. NE555. The other IC is a UM66 melody generator IC. one will provide a timer application in this circuit and the other will generate a melodious alarm.
Be careful while working with this circuit as you are dealing with the mains AC voltage so it can give you a lethal shock if you are not careful. And if you are not familiar with working with AC line voltages then do not attempt to make this circuit.
Hardware Components
| S.no | Component | Value | Qty |
|---|---|---|---|
| 1. | Bridge rectifier | 1N4007 | 1 |
| 2. | Main voltage line | 220V | 1 |
| 3. | IC | UM66 | 1 |
| 4. | IC | NE555 Timer | 1 |
| 5. | Resistor | 680Ω/5W, 270KΩ, 220KΩ, 560KΩ, 100Ω | 2, 1, 1, 1, 1 |
| 6. | Capacitor | 220µF/16V, 10nF, 0.1µF, 100µF | 1, 1, 1, 1 |
| 7. | Transistor | 2N3904 | 1 |
| 8. | Speaker | 8Ω | 1 |
Circuit Diagram
IC NE555 Pinout
IC UM66 Pinout
Working Explanation
The circuit is connected to the mains power supply, when the mains voltage will come back it will activate the circuit. now this AC voltage will be converted to DC through a bridge rectifier and then filtered through an electrolytic capacitor before going into the circuit. the 555 timers are working as a timer which will activate the UM66 IC that will generate a melody in the 8 ohms speaker amplified through a transistor 2N3904. The alarm runs for a few seconds and then goes off automatically. The time period of this running alarm depends on the 100uF capacitor. And to increase the output sound you change the transistor and use BD139 instead.
