Needed:
-Raspberry pi zero w
-mbus interface: google : «site:aliexpress.com usb to mbus slave»
-4x M3x8 pan head screw for plastic
-4x M4x8 pan head screw for plastic/M3 locknut and M3x10 machinescrew
-available space in a cabinet with a 35mm din rail.

The fitting to the din rail is a bit snug, but it does fit.

It could be redesigned to be quite a lot smaller, but this will do for now :)