hi,
i am tying to make a Zero crossing circuit with hysteresis using LM311, can any one please tell me what power supply (Vcc+ & Vcc-) should i use to make the its output suitable for inputting to microcontroller (or what current & voltage magnitude is suitable for microcontroller). & how to calculate the value of positive feed back resistor.

I have attached the cirsuit here with

Thank yu in advance.

 

There's no attachment.

 

If the signal is small (like from a radio headphone jack) you can skip the comparator and make the ZCD right at the microcontroller with a few components (cap, resistors, diodes).

Many microcontrollers already have comparators too.