A little searching comes up with this link:

https://lucidar.me/en/home-automation/linky-customer-tele-information/

The ‘power’ pins do not put out a 50Hz sine wave, but instead a 50kHz carrier with the 7-bit data amplitude modulated onto the carrier.

A digital DVM will most likely measure using dual slope integration, which will be much to slow to react to 50kHz. So it sees the signal as zero. The analogue meter will just have a half wave rectifier, ie, a series diode, so will produce a measurable waveform from the input.

The rectifier bridge produces a DC voltage as expected, which both meters will detect on DC voltage ranges.

Andrew

Er, which voltage regulator?  And what final voltage do you want, 5V or 3.3V?

0.68 Farad (that’s 680,000 microfarads) supercaps are £1.50 each in a pack of 5 from RS.  Working voltage is typically quite low, these are 3.6V.  Best to use a switched-mode buck converter down to 3.3V and if you need 5V a boost converter from 3.3V.  This is because the tolerance on the capacitors is -20 to +80% so if you put two in series to get a higher working voltage one of them may have a significantly higher voltage on it than the other depending on tolerance – of if you can measure the capacitance then try to get the closest matching pair from the batch.

If it isn’t obvious, don’t try connecting the supercap to the bridge-rectified 10V unless you buy one (actually an array) specified for say 16V – RS do sell these but they cost more like £150!  You can buy pre-built buck/boost converter boards for peanuts.  Use a conventional say 100uF electrolytic on the 10V then feed to the converter.

Low power electronics design is not straightforward, as in all engineering the devil is in the detail. It requires proper system design, careful consideration of power consumption at each stage and a detailed knowledge of the modules/components.

If there is a working solution, using wires, I’d stick with it. One could always put a LoRa, or other interface such as Bluetooth, at the point where the wires enter the house, and mains power is available. That way the information would be available throughout the house without the need to run extra wires everywhere.

From a simplicity viewpoint a linear IC regulator at the meter end is good. But to maximise the power available at the regulated output then I agree with JohnH that a buck converter is a better solution.

Be careful with super capacitors, read (and understand) the datasheets. When supercapacitors first came out they were used to backup RTCs and could only supply microamps. There are now supercapacitors that can accept/supply much higher currents. But as always they also have a premium price. For instance looking at some 0.68F supercapacitors from RS they have a DC impedance of 50 ohms. So with a current draw of 20mA that’s a 1V drop; not good!

Andrew

Solar panel and battery down by the gate? I can’t remember when I last looked at my smart meter display, when it first arrived we kept looking at it, but I know tumble dried s cost a lot, so we hardly use it, but if I want a cup of tea, the kettle us going on no matter what the meter says