Square wave generation

Its a triggering circuit that i want to build for firing the SCR's(used in the Rectifier Bridge). Problem is the the pulse to be fed to the SCR's has to be in synchronization with the A.C source to be fed to the SCR's. So Synchronizing this pulse would require first converting into A.C into Square Wave pulse...Friends recommmended to use lm324 as comparator for the circuit...Can anyone guide me on this first step?

The MOC3081 by ON/Motorola? E

yep..you r right..the MOC3081 by Motorola is used normally...but can it fire the SCR with the source given as A.C.??.as i already specified i have to generate the pulse for firing the SCR from the same A.C source that is going to be fed to the SCR...and what if donot use MOC3081..any other simple way?..thnks for the suggestion..

The datasheet shows such a circuit....E