[AVR] External clock as an input to MCU

[youngsinatra]

I'm using an AD7751 energy metering IC and ATMega32. I connect the PIN22 (CF) from AD7751 to PIN1 ((T0/XCK)PB0) from ATMega32. I want to calculate the energy by calculating the frequency from CF, how do I make this happen? I've set the operation mode to synchronous but I'm confused how to continue the program.. Please help.


Thanks

 

[KlausST]

Hi,

I want to calculate the energy by calculating the frequency

Frequency has nothing to do with energy. Each single pulse represents a certain amount of "energy".
If you want to calculate "total energy" you just need to count (integrate) the pulses and multiply the value with the "singke pulse energy".

**************
You need to measure frequency only, if you want to calculate "active power".

If you want this, then the first thing you need to decide:
* what range of frequency do you expect?

Then decide "frequency measurement method" you want/need to use.
* time measurement between pulses (for low frequencies)
* or "counting pulses for a known period of time" (for high frequencies)
--> there are a lot of "frequency measurement" threads in this forum, with code and discussions.

Then multiply the frequency with the "single pulse energy" to get active power.

Klaus

 

[youngsinatra]

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#include <avr/io.h>
#include <inttypes.h>
#include <avr/pgmspace.h>
#include <avr/interrupt.h>
#include <stdlib.h>
#include "LCD4bit.h"
#define F_CPU 1000000UL
 
volatile unsigned int Pulses, N;
 
 
ISR(TIMER0_OVF_vect);
ISR(TIMER1_OVF_vect);
 
int main(void)
{
    PORTB = 0;
    DDRB = 0xFC;
    DDRC = 0xFF;
    
    int i, j;
    float energy;
    char result[20] = "";
 
 
 
    MCUCR |= ((1 << ISC11) | (1 << ISC10)); //to count the pulse
    GICR |= (1 << INT0); 
    
    uint32_t elapse_time; // to count the time
    TCCR1A = 0;
    TCCR1B = 0x01;
    TIMSK = 0x04;
    
    N=0;
    TCNT1 = 0;
    
    sei();               
    for(i = 0; i<100 ; i++)
        for(j=0; j<1000; j++){;}
    elapse_time = N * 65536 + (uint32_t) TCNT1;
    cli();
    
    while(1)
    {
        energy = (3000 * Pulses * elapse_time) /3600000;
        dtostrf(energy, 3, 1, result);
        LCD_setCursor(4,0);
        LCD_Disp("Energy Meter");
        LCD_setCursor(0,1);
        LCD_Disp("Energy =");
        LCD_Disp(result);
        LCD_Disp("KWh");
    }
 
    
    return 0;
}
 
 
ISR(TIMER0_OVF_vect)
{
    // keep a track of number of overflows
    Pulses++;
}
 
 
ISR(TIMER1_OVF_vect)
{
    // keep a track of number of overflows
    N++;
}

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Here is my progress so far, are there any mistakes or my program is totally wrong?

 

[KlausST]

Hi,

Seems you neither did read post #2, nor the datasheet.

Klaus