I am using ESP8266 GPIO for ZCD (ZeroCrossing Detector). For this I am directly sensing 230Vac with 1M ohms resistor at GPIO. Here I am making use of snap-back circuit protection which is inbuilt to protect GPIO. I have no Idea of its current (amp) limitations as it is not mentioned in datasheet. I had been using this with other microcontrollers and works great.
Can someone help me with the spects.