MSP430F6736A: Finding voltage value from SigmaDelta ADC output

Hi 

The SD24 is a different input ADC it will minus DC voltage internally.

The Full-sale output depends on your OSR.  Con is not 24bit value base on your over sampling rate. 

Thanks for the reply.

i am getting a 28 bit output.I recalculated the output using 2^28.

But the value obtained is 1.309 and 1.415 for a sqare signal of 13.5Hz with 100mVpp amplitude and 50mV offset.

What is the value of the ADC in the register? Whether it can correctly reflect the voltage collected by ADC. Because I don't know what calculation you added in the software. What is the type of the variable of results[i] and voltage[i]?

results[] is of type unsigned long and voltage : float

I think the register is able to reflect the voltage collected by the ADC.
When I plot the values I get the sine wave and the calculated frequency is almost 13.5 Hz and Peak to peak value is almost 100mV(1.415 -1.309)

unsigned int resultsH[Num_of_Results], resultsL[Num_of_Results];
long unsigned int results[Num_of_Results],FR[Num_of_Results];

case SD24BIV_SD24IFG0:
resultsH[index] = SD24BMEMH0;// SD24MEM0 IFG
resultsL[index] = SD24BMEML0;// SD24MEM0 IFG
if (++index == Num_of_Results)
{
for(i=0;i<Num_of_Results;i++)
{
FR[i]=resultsH[i];
results[i]=(FR[i]<<16) |(resultsL[i]) ;
mean+=results[i]; // To find Mean(Zero crossing)

voltage[i]=(float)(results[i]*3)/con; // voltage value of SigmaDelta ADC Output
}

mean=mean/Num_of_Results; //To find Mean(Zero crossing)
for(i=0;i<Num_of_Results;i++)
{
r[i]= results[i]-mean; //Removing the offset
voltage_r[i]=(float)(r[i]*3)/con; // voltage value of shifted signal
}
}

When I remove the mean value from the results[] and calculate the voltage it is almost in the range -50mV to 50mV.

Hi Anusree,

Got your questions, I can join and try to help you quickly.

Thanks!

Best Regards

Johnson 

Have you watch the mean value in debug mode? You could add all the variables in the watch expression to find which intermediate variables is not performed as excepted.