The purpose of this project is to construct a Microcontroller based security system that continuously monitors the voltage readings and protect the circuit from over and under voltages. Sudden fluctuation in supply is a very big problem in industries and domestic applications. It causes a major loss for industries, offices and homes. This project gives a low cost and powerful solution for this problem. This Circuit protects refrigerators ACs, Microwave ovens as well as other appliances from over and under voltage fluctuations.   These circuit employes a 12V SPDT relay that is used to control the Load. An NPN transistor is used to drive the relay.  An LED is connected across the relay for visual indication of relay position. This project uses regulated 12V, 500mA power supply. 7812 three terminal voltage regulator is used for supply voltages. Bridge type full wave rectifier is used to rectify the ac out put of secondary of 230/12V step down transformer   The main controlling device of the whole system is a Microcontroller. Voltage sensor and relay switch are connected to Microcontroller. The house hold supply is continuously monitored by the microcontroller. If over voltage or under voltage is detected, it controls the relay switch to break the power supply of the house. To perform the task, Microcontroller is loaded with an intelligent program written in embedded ‘C’ language.    

The main objectives of the project are:

1. Automated over voltage and under voltage monitoring.
2. Break down of house hold supply in case of abnormal voltages.
3. Faster response to the situation.

  The major building blocks of this project are:

1. Regulated Power Supply.
2. PIC Microcontroller.
3. Relay with driver
4. Crystal
5. Voltage sensor
6. Reset.
7. LED Indicators.

      Software’s used:    

1. PIC-C compiler for Embedded C programming.
2. PIC kit 2 programmer for dumping code into Micro controller.
3. Express SCH for Circuit design.

    Regulated power supply:

       

Block Diagram:      

video: