Building the 'powerpi' power usage monitor for TechInc The raspberry PI in the mains-box is powered by a small power-module in the second row, next to the single (schuko) powersocket. The purpose of it is to interpret the S0-output (100-pulse-per-KW/h) coming from the [Driefazige kWh-teller DSz15D-3x80A] which is mounted on the most bottom rail.
Some info on how to connect something to the S0 bus can be found here: File:S0-bus application note.pdf
A good bit of info about working with Optocouplers can be found [here]
sudo apt-get install ttf-freefont
sudo apt-get install ttf-wqy-zenhei