Yes, I mean AC240V, measure current, not voltage, and I do not want to use CT which not easy to get and bulky.
There is such circuit, it use shunt resistor, voltage drop across shunt connect to optocouple input, but opto input need 1.2VDC, so there is a rectifier and pre bias voltage on optocouple input, using CTR (current transfer ratio) , we measure output of opto which is the current under measure.
This is what i remember, but I forgot exactly how the pre -bias circuit work.
BTW, what is di/dt sensor ?