True enough, but my old PC has a serial port.
I already have a uP onsite measuring temperature.
Voltage and current are next.
donald
I have a simple current system in use that uses an old tape recorder
playback head glued against one of the main leads, followed by a peak
detector.
You likely need no RMS, but if you use a 50Hz (or 60Hz US) lowpass, and
use a PIC with a ADC, you will have several channels analog input, and you
could take a lot of samples and get peak-to-peak value, and calibrate once
against a real meter (So 110V would be 110 x 2 x sqrt(2) = 311V,
100x attenuator gives 3.11V peak peak on the ADC).
The PIC will have RS232 or you can do it in software, add a MAX232.
You could even FM modulate that signal and send it via the mains.
As you already have temp, you maybe already have the ADC, and maybe enough
channels, else multiplex with some 74HC405x CMOS switch.
Main isolation, well you likely already have a transformer, grab and measure
the secondary for voltage, if no transformer and powered by for example RTG
or polonium 210, you could generate current for an optocoupler via capacitive
coupling if you want o be exotic, and the current in the photo-transistor
at the other end of the optocoupler would be proportional to the input mains
voltage.
Or buy a transformer.
There are many other ways I will not discuss these in this limited space as I
am watching telly on this PC now, and looks like I have to zap again.
If you made it this far thank you for your attention span.