Useful resources for this https://dextrel.net/dextrel-start-page/design-ideas-2/mains-zero-crossing-detector https://www.eevblog.com/forum/projects/mains-zero-crossing-detection Zero crossing detect ICs https://www.rohm.com/products/power-management/ac-voltage-zero-cross-detection-ics/bm1z001fj-product

The circuit below provides a simple method to detect a mains voltage input with an input range of 90 – 240V AC: The output gives a low signal for around 90% of the time when a mains input is present, so you need to connect it to an edge detect input of a microcontroller (e.g. […]