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By btidey
#74128 Are you saying it never fires the interrupt?

If the pulse is going low for a period of 200uSec then the esp8266 should be handling that easily and then I don't think it is a speed problem.

How are you testing it manually? Are you sure the output pulse is driving the esp pin properly high and low? You have the pin specified to use the input internal pullup but that is quite a high value resistor (~36K). Depending on the output from the sensor you might need to use a lower value external pull up.