Current Sensor

ACS712 is a hall effect-based linear current sensor that can measure both AC and DC current. Let’s look at the connection and steps to interface.

For a unipolar supply voltage, it nominally remains at VCC⁄ 2. Thus, VCC = 5 V translates into V _IOUT(Q) = 2.5 V. So for 0A the reference voltage is V_ADC = 2.5V and ADC Value is 512.

Current sensing value is

V_out = (V_CC/2) + Sensitivity*Current , Here V_CC = 5V

Here, ADC Value = V_out * (1024/5)

                            = ((V_CC/2) + Sensitivity*Current)* (1024/5) =  ((5/2) + Sensitivity*I)* (1024/5)

                             = 512 + (Sensitivity*I*1024)/5

Current I = (5/(1024* Sensitivity))*(ADC Value-512)

For ACS712ELCTR-20AT the sensitivity is 0.1 and the current value is Current I = (5/102.4)*(ADC Value – 512)

float current(uint8_t phase,uint8_t channel)
{
  float current;
  uint16_t ADC_Value;
  ADC_Value=read_adc(channel);
  if(phase==AC_Current)
	{
		if(ADC_Value>=512)
			{
			 current=(ADC_Value-512)*(5/(ADC_Scale*sinsitivity)); //VCC=5V
			}
	}
     else if(phase==DC_Current)
	{
		current=(ADC_Value-512)*(5/(ADC_Scale*sinsitivity)); //VCC=5V
	}
	
 return current;
}

Here for ACS712-05BT sensitivity 0.185, ACS712-20AT sensitivity 0.1 and ACS712-30AT sensitivity 0.066.

Set timer0 overflow vect and at every interrupt service routine read the current. Let’s look at the main program-

  #include<avr/io.h>
  #include<stdio.h>
  #include<avr/interrupt.h>
  #include"adc.h"
  #include"lcd.h"
float VA=1,Amp_ac,Amp_dc,volage=220;
char str[20];
int main(void)
  {
   LCD_INIT();
   adc_init();
   LCD_Clear();
   timer_ISR();
   while(1)
    {
      sprintf(str,"AC Current=%.2fA",Amp_ac);
      LCD_write_string(1,1,str);
      sprintf(str,"DC Current=%.2fA",Amp_dc);
      LCD_write_string(1,2,str);
      _delay_ms(1000);
    }
  return 0;
}
ISR(TIMER0_OVF_vect)
{
	Amp_ac=current(1,0); //AC Current(1) with channel 0
	Amp_dc=current(2,1); //DC Current(2) with channel 1
	
}

Since we have a PDB supply is fixed at 220V, we can calculate the power = VIcosՓ. If power factor cosՓ=0.98 and V=220V then we can calculate the power from the equation.