Two simple circuits (electrically isolated and non-isolated) of zero-crossing detector of main's AC.

• Article (rus): https://cxemka.com/62-detektor-perehoda-cherez-nol-s-galvanicheskoi-razvjazkoi-i-bez-neyo.html
• Youtube (sub): https://www.youtube.com/watch?v=oTmkZlAcVUI

• STM32F103C8
• STM32CubeIDE
• HAL