I need some explain how does comparator work as zero cross detection and integrated amp
1) There is no comparator, instead the LM324 is a very slow quad opamp. 2) The 1m resistors are a dead short, they are probably 1M which is 1 million ohms. 3) The total gain is 12195 so a very small signal produces a saturated output. 4) The LM324 is so noisy that with the gain that is so high, I think its output will be its own noise at a saturated output level.