The greatest problem with these sensors is electrolysis and subsequent oxidation, due to the DC current flowing through the sensor in a humid environment.
There are some solutions: Most of the circuits that supposedly feed the sensor with A are bogus as it is apulsed DC at best..
One could try a capacitive sensor...... in theory very good but in practice plagued by issues.

What I have done is to remove constant current from the sensor by feeding it from a transistor that I can switch on and off. I take a measurement every 2-6 hrs and switch the current off in between. Makes a huge difference

@jpaulin Looking good. And I mean GOOD

@scalz A very late reply, but someone else might be helped with it.
Hardware SPI is working.
The onnly thing is that on W5100 shield it will work without any problem but with most 5100 modules you need a small modification fixing w5100 problems

@Anticimex I do agree. It CAN be used, but it is just a bad choice as the ethernet libraries do not leave much space for much else.
ENC28J60 in that aspect is worse than the W5100.
I tried it more like a proof of concept and it does work pretty well just passing data, but I put everything on an ESP8266. OK, WiFi rather than Ethernet but thats OK for me

@dynamite yes i do not see a problem in measuring the amplitude. I am not sure if, when measuring current through a CT, the frequency will change, as that is just the grid frequency, but probably you were referring to its use in measuring gas flow.

My idea to use a dedicated attiny is simply so the ESP will be freed of the burden of calculation/measuring, as this will be a rather continuous process. The code will probably fit an attiny13, but I have never tried i2c on an attiny13, but I have on an attiny85, so i am pretty sure it will work on the 25 and 45 as well. The 13 I still have to try

@dynamite indeed, that is why i was looking at yr code. On the other hand, if the frequency is known and you know the amplitude, you can make a calculation.... but then again, in order to know the amplitude you need a series of measurements.
Thats why i was thinking to let a dedicated attiny do that: all it needs to do is to measure and put the result in its I2C registers. The esp8266 then can do a hoist of other things and just pull the powerparameters when needed

@Yveaux yes, As a matter of fact I looked into that one, I think they can be had for 60cts, but the 'problem' is they need a galvanic connection to the grid and to the esp as well. I want it to be completely isolated from the grid

@dpcr thanks, indeed, I am using a CT as well, adding a dc bias, still balancing between just measuring the amplitude of the sinus, or measuring all along the sinus. I think i will have an attiny 25 or ideally an attiny13 do this as a dedicated I2C slave and have that read by an ESP8266. Ofcourse there is the sonoff Touch, but thats a tadd too much to put on a large number of devices.

@dpcr Thanks, yes i read how you did it with locating the sweet spot, but I was thrown off by the 'no magnet' statement.
'connecting' my meter is also still in the cards, no idea if it has a magnet or not (in which case i may use a Hall sensor), otherwise i may try the magnetometer

@dynamite thanks, i know pretty well how the magnetometer works, but I guess i was thrown off by the statement 'no magnet', but I guess it must be weak magnetization of the various parts then

@dpcr very interesting, I may use some of your sine measuring approach in a powermeter i make.

Nevertheless, i have a question: you say you have no magnet in yr meter, so what is it the magnometer is actually picking up?

@jpaulin OK, thanks. Just seemed like a rather long antenna in the picture.
I am using this antenna, with very good results. Better than the 1/4 wavelength whip

@jpaulin Thanks, that is good to know. I have the RFM69 HW running with a W5100/Promini. W5100 module needed a bit of a hardware tweak for SPI, but works well. Now I probably would have opted for the 5500 as well.
I just use it to communicate between two properties at some 500 meter distance, most sensors I use are attached to ESP8266

Seems like a rather long Antenna on yr module. What frequency are you on?