VAT meter using ATMega8

June 18, 2024 Roberto Magalhães

When measuring voltage and current with a multimeter, the test leads must be changed carefully. There is a probability of damaging the multimeter if the voltage is mistakenly measured in high current mode. If voltage and current are measured at the same time, we have to use two multimeters and care must be taken when connecting both multimeters. The VAT meter is a combination of voltmeter, ammeter and thermometer. It can measure voltage and current simultaneously along with temperature.

The project is built on ATMega8. Therefore, the reader must have knowledge of how to start with AVR and interface LCD with AVR. It used ACS-712 current sensor to measure current and voltage is measured by ACD terminal. There are two temperature sensors used in the circuit which can measure the temperature of two different places like transformer, voltage regulator or any heating component. All data can be observed on a 16×2 LCD display. This project can measure and display maximum voltage up to 50Volts DC and maximum current up to 20Amps DC. When the voltage exceeds 45 VDC or the current exceeds 15 A or the temperature exceeds 70 degrees, the display flashes the parameter close to the specific value and a beep is generated. Required components –

Block diagram –

Fig. 1: Block diagram of VAT METER using ATMega8

Circuit Connections – This device is based on the AVR ATMega8. ATMega8 is an 8-bit microcontroller that can operate up to 16 MIPS of transfer rate clocked at 16 MHz. Here we are using ATMega8's internal RC oscillator which provides fixed clock rate of 1.0 2.0 4.0 or 8, 0 MHz, then set your ATMega8 internal RC oscillator to 1 MHz. ATMega8 is interfaced with 16×2 LCD, L M35 and ACS712 to make the device. There is a Trimpot (shown as VR1 in the circuit diagram) which is used to adjust the contrast of the LCD. There is a yellow LED with a parallel interface to the entire circuit that is used to indicate that the circuit's power supply is working properly. There is a blinker connected to bit 0 of port D of the ATMega8 which indicates that the MCU is working. Two LM35 temperature sensors are used to obtain the temperature state at two different locations. Both LM35 are connected to bits 1, 2 of port C of the ATMega8, which are pins 1 and 2 of the ADC. The ACS712 current sensor is used to measure current through a series connection with a DC power supply. The OUT pin of the ACS712 is connected to bit 0 of port C of the ATMega8 which is pin 0 of the ADC. The voltage is measured by bit 3 of port C of the ATMega8, which is pin 3 of the ADC. diagram) which is used to calibrate the voltage. The BC548 transistor is used to drive the buzzer. The base of the transistor is connected to bit 1 of port D of the ATMega8. The collector of the transistor is connected to the buzzer and the emitter is connected to ground. AREF or 21st pin of ATMega8 is connected to 5v via 10mH inductor and there is also a 0.1uf capacitor connected between ground and AREF. The entire circuit operates on 5V DC which can be obtained from a 5V power bank or 9V battery with 5V regulated power supply using 7805 IC. The internal RC oscillator (1 MHz) used with ATMega8, so there is no need to add external oscillator. How the circuit works – After assembling the circuit, the ISP port of the ATmega8 must be connected to any AVR programmer and the VATmeter.hex file must be updated on the microcontroller. Then disconnect the AVR programmer circuit. Now the device is ready for operation. When the device is turned on, the flashing LED starts flashing and the LED displays “Welcome to VAT METER”. After a few seconds, the LCD enters a stable state that displays the voltage, amp and temperature of both sensors and updates the data as per the sensor input update. While we connect the DC power supply in series with the ACS712 current sensor as shown in the circuit diagram. The LCD shows battery voltage and current. Make sure the Load is connected in series with the battery and the ACS712 current sensor so that current can be measured through the Load. The temperature sensor can be placed close to the heating component to measure the temperature. If the temperature exceeds 70 degrees centigrade or the voltage exceeds 45 VDC or the current exceeds 15 ACC, the display will flash the parameter close to the specific value and an audible signal will be generated via a buzzer.

Fig.1: Image showing the operation of the VAT METER

Programming guide – This device is based on AVR ATMega8 and is programmed with embedded C using AVR Studio 4. Other programming tools such as Atmel Studio or Notepad++ can also be used to write and compile the code. The ATMega8 is programmed to measure Voltage, Current and Temperature at the same time on a single display. This project can measure voltage up to 50Volts DC and maximum current up to 20Amps DC. Constants used in the code – #define F_CPU 1000000L :- Constant used to define the MCU clock frequency #define BLINKER 0b00000001 :- defines the blinking LED for bit 0 of port D #define ALARM 0b00000010 :- defines buzzer connected to bit 1 of port D #define LCD_DP PORTB: – Port B defined as LCD data control port #define LCD_CP PORTD: – Port D is defined as LCD control port #define LCD_EN 0b10000000 : – The EN pin of the LCD is connected to 7 bits of port D #define LCD_RS 0b01000000 : – The RS pin of the LCD is connected to 6 bits of port D Variable used in the code – AMP long = 488; : – To calculate ampere value to ADC value internal VOLTS=0; : – To store the voltage value long AMPS = 0L; : – To store the current value intTEMP1=0; :- To store the temperature of the first sensor int TEMP2 = 0; :- To store the temperature of the second sensor char DST(8); :- To display the value on LCD long A=0; : – To initially store the ADC value inner loop = 0; :- To control the parameter blinking on the LED internal alarm = 0; : – To control the doorbell int temparray1(5)={25,25,25,25,25}; : – To store 5 temperature values for average temperature int temporray1pos=0; :- To select temperature matrix value int temparray2(5)={25,25,25,25,25}; : – To store 5 temperature values for average temperature int temporray2pos=0; :- To select temperature matrix value Header file and libraries used in the code – #include : – Standard AVR header for input/output #include : – Standard AVR header to provide time delays Function used in the code – initPorts: – To initialize the port as input or putput LCD_enable: – To control LCD EN pin LCD_WriteCmd: – write command for LCD LCD_init: – To initialize the LCD at the beginning LCD_RowCol: – To set the cursor position LCD_ClrScr: – To clean the LCD display LCD_writeCh: – Writes character on LCD display LCD_writeStr: – Writes String to the LCD display ADC_init: – To initialize ADC ADC_read: – Read the ADC value showValue: – Show value in specific format _delay_ms: – For time delay Algorithm – The code for this VAT METER using ATMega8 works as follows. When the VAT meter circuit is turned on, firstly, the port that defines port B and port D as output is initialized. port C set as input. void boot ports ( ) { DDRB = 0xFF; DDRD = 0xFF; DRC = 0x00; } After port initialization, the blinking LED was set to High for some delay and then inverted (set to LOW). Additionally, the LCD initializes. PORTD = BLINKER; _delay_ms (2000); LCD_init ; _delay_ms(100); PORTD &= (~BLINKER); Firstly, the LCD is cleaned to remove any kind of junk values. Then set the cursor to print “Welcome to” massage on the first line and “VAT METER” on the second line. LCD_ClrScr ; LCD_RowCol (1, 1); LCD_writeStr(“Welcome to”); LCD_RowCol (2, 7); LCD_writeStr(“VAT METER”); Now the ADC is initialized and reading all ADC channel values. Then the LCD was cleared to remove the welcome massage. ADC_init ; _delay_ms (2000); for (int i=0; i<10; i++ ) { ADC_reading (i/2); } LCD_ClrScr ; We enter the while loop, here the loop variable used which flashes the parameter on the LCD every cycle while any value exceeds the set value. alarm set to LOW. Blinker LED set to blink every cycle, which indicates that the MCU is working. if (loop==0) loop = 1; other cycle = 0; alarm = 0; PORTD ^= FLASHES; Read the ACD value from channel 3 and store it in variable A. ADC value divided by 2 to maintain the approximate maximum range of 50 volts. LCD cursor placed in its position to print the value in specific format. If the voltage value exceeds the 45 Volt range, the “V” parameter on the LCD will flash and the buzzer will beep. A = ADC_reading(3); _delay_ms(5); LCD_RowCol(1, 1); VOLTS=A/2; showValue(VOLTS); if (VOLTS>450 && loop==0) { LCD_writeStr(””); alarm = 1; } other LCD_writeStr(“V”); Now set A to zero to read another ADC value from channel 0. Some calculations require converting the ADC value to Ampere value. Once we get the ampere value, just print it on the LCD. When the current exceeds the set range of 15 A, the parameter flashes on the LCD and the buzzer beeps. A = 0; ADC_reading(0); _delay_ms(5); for (int i=0; i<10; i++ ) { A = A + reading_ADC ( 0 ); _delay_ms(5); } A = 5110-A; AMPS = (A * AM FACTOR) /10000L; LCD_RowCol(2, 1); showValue (AMPS); if ((AMPS>150 AMPS<-150) && loop==0) { LCD_writeStr(””); alarm = 1; } other LCD_writeStr(“A”); Set A to zero and read the value from ADC channel 1. Here 5 temperature values are taken for each cycle to get the average temperature value. When the temperature value exceeds 70 degrees, the parameter flashes on the LCD and the buzzer beeps. A = 0; ADC_reading(1); _delay_ms(5); for (int i=0; i<10; i++ ) { A = A + ADC_read(1); _delay_ms(5); } TEMP1 = A/2; temparray1(temparray1pos++) = TEMP1; TEMP1 = (temparray1(0) + temparray1(1) + temparray1(2) + temparray1(3) + temparray1(4) )/5; if (temparray1pos>4) temparray1pos = 0; LCD_RowCol (1, 9); showValue(TEMP1); if (TEMP1>700 && loop==0) { LCD_writeStr(””); alarm = 1; } other { LCD_writeCh(223); LCD_writeCh('C'); } Set A to zero and read the ADC channel 2 value. Here, 5 temperature values are taken for each cycle to get the average temperature value. When the temperature value exceeds 70 degrees, the parameter flashes on the LCD and the buzzer beeps. A = 0; ADC_reading(2); _delay_ms(5); for (int i=0; i<10; i++ ) { A = A + ADC_read(2); _delay_ms(5); } TEMP2 = A/2; temparray2(temparray2pos++) = TEMP2; TEMP2 = (temparray2(0) + temparray2(1) + temparray2(2) + temparray2(3) + temparray2(4) )/5; if (temparray2pos>4) temparray2pos = 0; LCD_RowCol (2, 9); showValue(TEMP2); if (TEMP2>700 && loop==0) { LCD_writeStr(””); alarm = 1; } other { LCD_writeCh(223); LCD_writeCh('C'); } If the alarm variable is high, emit a beep through pin 1 of port D. if (alarm) PORTD = ALARM; _delay_ms(150); PORTD &= (~ALARM); _delay_ms(60); Check out the full code and quickly start building this exciting project.

Project source code

 ###

 //Program to
 / *

 filename: VATmeter.C

 author: f.hassan

 date: 10-03-2018

 MCU: ATmeaga8

 display: LCD 16x2

 */


 #define F_CPU 1000000L



 #define BLINKER 0b00000001

 #define ALARM 0b00000010

 //================================================ =================================

 #include

 #include


 #define LCD_DP PORTB

 #define LCD_CP PORTD

 #define LCD_EN 0b10000000

 #define LCD_RS 0b01000000


 long AMPFACTOR = 488; // for 20A

 int VOLTS=0;

 long AMPS=0L;

 int TEMP1=0;

 int TEMP2 = 0;

 char DST(8);

 //================================================ =============================

 void initPorts ( )

 {

 DDRB = 0xFF;

 DDRD = 0xFF;

 DDRC = 0x00;

 }

 //================================================ =============================

 void LCD_enable ( )

 {

 LCD_CP = LCD_EN;

 _delay_us(50);

 LCD_CP &= (~LCD_EN );

 _delay_us(30);

 }

 //================================================ ===========================
 
void LCD_WriteCmd ( unsigned char cmd )

 {

 LCD_CP &= (~LCD_RS );

 LCD_DP = cmd;

 LCD_enable ( );

 }

 //================================================ =============================

 void LCD_init()

 {

 unsigned char initval = 0x30;


 _delay_ms ( 50 );

 LCD_WriteCmd ( 0x30 );

 _delay_ms ( 20 );

 LCD_WriteCmd ( 0x30 );

 _delay_us ( 200 );

 LCD_WriteCmd ( 0x30 );

 _delay_ms ( 100 );


 initval = 0b00001000;

 initval = 0b00000100;

 LCD_WriteCmd ( initval );

 _delay_ms ( 25 );


 LCD_WriteCmd ( 0x0C );

 _delay_ms ( 25 );


 LCD_WriteCmd ( 0x06 );

 _delay_ms ( 50 );


 }

 //================================================ =============================

 void LCD_RowCol ( unsigned char R, unsigned char C )

 {

 switch (R)

 {

 case 2: LCD_WriteCmd ( 0xC0 + C-1 ); break;

 case 1:

 default: LCD_WriteCmd (0x80 + C-1); break;

 }

 _delay_ms ( 3 );

 }

 //================================================ =============================

 void LCD_ClrScr ( )

 {

 LCD_WriteCmd ( 0x01 );

 _delay_ms(3);

 }

 //================================================ =============================
 
void LCD_writeCh ( unsigned char ch )

 {

 LCD_CP = LCD_RS;

 LCD_DP = ch;

 LCD_enable ( );

 }

 //================================================ =============================

 void LCD_writeStr ( char s )

 {

 for (int i=0; s(i)!=0; i++)

 {

 LCD_writeCh ( s(i) );

 _delay_us ( 20 );

 }

 }

 //================================================ ========================================

 void ADC_init ( )

 {

 ADCSRA = ( (1 << ADPS2) (1 << ADPS1) (1 << ADPS0) (1 << ADEN) );

 }


 //================================================ ========================================


 int ADC_read (int cno)

 {

 ADMUX = (cno%4);

 ADCSRA = (1 << ADSC);

 while (ADCSRA & (1 << ADSC));

 return ADC;

 }


 //================================================ ========================================

 void showValue(int vin)

 {


 int V = vin;


 if ( V < 0 )

 {

 DST(0)= '-';

 V = V * -1;

 }

 else

 {

 DST(0)= ' ';

 }

 DST(1)=V/1000 + '0';

 V=V%1000;

 DST(2)=V/100 + '0';

 V=V%100;

 DST(3)=V/10 + '0';

 DST(4)='.';

 DST(5)=V%10 + '0';

 DST(6)=0;

 
if (DST(1) == '0' && DST(2) == '0')

 {

 DST(1) = ' ';

 DST(2) = ' ';

 }


 if (DST(1) == '0' )

 DST(1) = ' ';


 LCD_writeStr ( DST );


 }

 //================================================ ========================================


 int main()

 {


 longA=0;

 int loop = 0;

 int alarm = 0;

 int temparray1(5)={25,25,25,25,25};

 int temparray1pos=0;

 int temparray2(5)={25,25,25,25,25};

 int temparray2pos=0;

 _delay_ms ( 100 );

 initPorts ( );


 PORTD = BLINKER;


 _delay_ms ( 2000 );

 LCD_init ( );


 _delay_ms ( 100 );


 PORTD &= (~BLINKER);

 LCD_ClrScr ;

 LCD_RowCol ( 1, 1 );

 LCD_writeStr ( "Welcome to" );

 LCD_RowCol ( 2, 7 );

 LCD_writeStr ( "VAT METER" );



 ADC_init ( );

 _delay_ms ( 2000 );


 for (int i=0; i<10; i++)

 {

 ADC_read ( i/2 );

 }


 LCD_ClrScr ;


 while(1)

 {

 if (loop==0)

 loop = 1;

 else

 loop = 0;

 alarm = 0;

 PORTD ^= BLINKER;

 A = ADC_read(3);

 _delay_ms ( 5 );

 LCD_RowCol ( 1, 1 );

 VOLTS = A / 2;

 showValue ( VOLTS );

 if (VOLTS>450 && loop==0)

 {

 LCD_writeStr ( " " );

 alarm = 1;

 }

 else

 LCD_writeStr("V");



 A = 0;

 ADC_read ( 0 );

 _delay_ms ( 5 );

 for (int i=0; i<10; i++)

 {
 
A = A + ADC_read ( 0 );

 _delay_ms ( 5 );

 }

 A = 5110-A;

 AMPS = (A * AMPFACTOR) /10000L;

 LCD_RowCol ( 2, 1 );

 showValue ( AMPS );

 if ( (AMPS>150 AMPS<-150) && loop==0)

 {

 LCD_writeStr ( " " );

 alarm = 1;

 }

 else

 LCD_writeStr("A");


 A = 0;

 ADC_read(1);

 _delay_ms ( 5 );

 for (int i=0; i<10; i++)

 {

 A = A + ADC_read ( 1 );

 _delay_ms ( 5 );

 }

 TEMP1 = A/2;

 temparray1(temparray1pos++) = TEMP1;

 TEMP1 = (temparray1(0) + temparray1(1) + temparray1(2) + temparray1(3) + temparray1(4) )/5;

 if (temparray1pos>4)

 temparray1pos = 0;

 LCD_RowCol ( 1, 9 );

 showValue ( TEMP1 );

 if (TEMP1>700 && loop==0)

 {

 LCD_writeStr ( " " );

 alarm = 1;

 }

 else

 {

 LCD_writeCh ( 223 );

 LCD_writeCh ( 'C' );

 }


 A = 0;

 ADC_read(2);

 _delay_ms ( 5 );

 for (int i=0; i<10; i++)

 {

 A = A + ADC_read ( 2 );

 _delay_ms ( 5 );

 }

 TEMP2 = A/2;

 temparray2(temparray2pos++) = TEMP2;

 TEMP2 = (temparray2(0) + temparray2(1) + temparray2(2) + temparray2(3) + temparray2(4) )/5;

 if (temparray2pos>4)

 temparray2pos = 0;

 LCD_RowCol ( 2, 9 );

 showValue ( TEMP2 );
 
if (TEMP2>700 && loop==0)

 {

 LCD_writeStr ( " " );

 alarm = 1;

 }

 else

 {

 LCD_writeCh ( 223 );

 LCD_writeCh ( 'C' );

 }


 if (alarm)

 PORTD = ALARM;

 _delay_ms ( 150 );

 PORTD &= (~ALARM);

 _delay_ms ( 60 );


 }


 return 0;

 }

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