my project is to make power factor meter,
my approach is to find out the zero crossing of both Current and Voltage,
find out the time difference and then calculate the angle

can anyone tell me which zero crossing detector i should use,
i am using 8051 mc,

other ideas are highly appreciated

 

You can use a comparator such as an LM339 quad which will give you a digital output change at the zero crossing. You should add some hysteresis feedback to avoid oscillations around the zero point.

You do know that the zero crossing scheme only works accurately if both the current and voltage are pure sine waves with little distortion(?).

 

crutschow beat me to it about it only working with sines.

Take a look at http://www.splatco.com/tips/pwrfact/pfarticl.htm

Some of my EE101 is coming back to me.