I am trying to sense the power factor angle using microcontroller.

Now the mechanism that I have thought it that

1. Measure the zero crossing of voltage
2. When the voltage zero is sensed, start the timer of micrcontroller and then start sensing the zero of current.
3. But how to sense zero of currrent? By using a zero crossing current circui

My problem: I have made zero voltage circuit using transistor and opamps. The transistor is dependant upon the voltage applied between the emitter and base.When the voltage is zero, the transistor is off and the collector 5 V pulse is obtained accross collector and emitter.

But what for current? Is there any electronic device that is turned on/off by current ?

So I think the only solution is to convert the current into voltage and then sense the zero of voltage? Is it a viable solution?