Has someone tried this zero crossing detector:

   Power Xformer
   secondary       1M               1M
 +--uuuu---O-------/\/\/\-----+-----/\/\/\-----O + 5V (PIC Vdd)
 |         |                  |
===        v                  v

         To rectifier       To PIC pin

This has the advantages of good protection, simplicity and rather accurate
zero detection even with low transforemer voltages. It can also be used
with a center-tapped xformer.

anyone ?

Peter