A simple project for beginners in AVR platform

1. Smart under and over voltage
protection system for home
Represented by : Shuvadip das
id : 021141086
course: energy conversion lab
sec: c

2. Introduction :
• This project is designed which automatically turn on and turn off main power supply in case of
issue in AC main power supply and on one need to control it manually
• It is designed to insure protection of home devices like fan, light lamps, television, refrigerator
and all other things you need to protect in case of under and over voltage in main supply
• Microcontroller is embedded into this system to make it smart enough to handle all the issues
intelligently and to provide control signals to turn on and off AC main power supply.

3. Component description :
• Voltage sensor :
Voltage sensor is used to measure voltage of AC main power supply. Voltage sensor is used difference amplifier to to step down
voltage level from 220 volt AC to 2.8 volt AC or 311 volt peak of AC voltage to 3.96 volt of peak voltage of sine wave.
Difference amplifier is used as a signal conditioning circuit to convert high voltage of AC main supply into low voltage which
microcontroller can easily read. Because microcotroller analog to digital converter can not read voltage more than 5 volt and
voltage more than 5 volt damage microcontroller.
• High speed relay :
Relay is used to turn on and turn off main power supply. Relay get control signal from microcontroller through a transistor.
Diode is use in parallel with coil pin of relay to avoid sparking in case of back emf. Because coil is made of inductive material.
Selection of relay depends on load of your home. For example maximum load of your home devices is 10 ampere. So should use
10 ampere relay. Another important thing while selecting relay for this circuit is switching speed of relay. Your relay speed
should be as fast as possible. Because more the switching speed of relay, more protection it will provide to your devices by
turning them on or off in minimum possible time.

4. Component description : (continued)
• Liquid crystal Display :
LCD is used to display value of voltage and status of your power supply. If AC voltage of main
power supply is greater than 20% of normal operating voltage, LCD display ” fault occur”. Otherwise
LCD display ” No fault”. LCD also displays value of AC main voltage supply.
• Voltage regulators :
7805 and 7812 is used to get regulated 5 and 12 volt which is supply voltage for microcontroller
and relay respectively. 220 to 12 volt step down transformer and rectifier full bridge is used to
produce DC voltage which is input of voltage regulators.

5. Circuit Diagram :

6. Circuit Diagram : ( description)
• Circuit diagram of under and over voltage protection system is shown below. I
have used just a lamp for simulation in this circuit. But you should connect this
circuit at main panel of your home from where AC main power supply
connections have taken for your home devices. Circuit diagram below shows
when voltage is 220 volt AC or less than of normal operating voltage lamp is on
and relay is working. Because relay is used as normally closed mode. But when
voltage become greater than or less than normal operating voltage it will turn
off relay in minimum possible time and relay in return turn off main AC power
to ensure safety of devices.

7. AVR Code :
#include <avr/io.h>
#include "LCD.c"
void InitADC() {
ADMUX=(1<<REFS0)|(0<<REFS1); // For internal vref=2.5V;
ADCSRA=(1<<ADEN)|(1<<ADPS2)|(1<<ADPS1)|(1<<ADPS0);
//Rrescalar div factor =128
}
uint16_t ReadADC(uint8_t ch) { //Select ADC Channel ch must be 0-7
ch=ch&0b00000111;
ADMUX|=ch;

8. //Start Single conversion
ADCSRA|=(1<<ADSC);
//Wait for conversion to complete
while(!(ADCSRA &
(1<<ADIF)));
//Clear ADIF by writing one to it
//Note you may be wondering why we have write one to
clear it
//This is standard way of clearing bits in io as said in
datasheets.
//The code writes '1' but it result in setting bit to '0' !!!
ADCSRA|=(1<<ADIF);
return(ADC);
}
void Wait() {
uint8_t i;
for(i=0;i<20;i++)
_delay_loop_2(100);
}

9. float voltage_READ(void)
{
float max,v;
int i;
float t[40];
for(i=0; i<=39; i++)
{
v= ReadADC(0); //Digital value convert
v =v*(5.0/1023.0);
//v=(v-5.0);
t[i]=v;
}
//ADCSRA|=(0<<ADSC);
max=t[0];
for(i=0; i<=39; i++)
{
if(max<t[i])
max=t[i];
}
max=max*300/3.871;
lcd_gotoxy(1,2);
lcd_printf(max);
lcd_print(" V");
_delay_ms(1000);
return(max);
}

10. void main()
{ PORTA=0xFF;
DDRD=0xFF;
float adc_result,result,v;
int adc_int[40];
int max,i,adc;
//Initialize LCD
lcd_init();
//lcd_clear();
//Initialize ADC
InitADC();
//Put some intro text into LCD
lcd_gotoxy(0,1);

11. lcd_print(" LOAD PROTECTION");
while(1)
{
//Lcd_out(1,1, "Voltage:");
_delay_us(10);//for avoiding spike problem
result=voltage_READ();
if (result>250)
{PORTD=0xFF;
}
if(result<250)
{PORTD=0x00;}
}
}

12. Modification
We can also add more functionality
in this project by adding GSM to
send value and status of AC main
power supply to your home cell
number

13. Thank you