This Raspberry Pi RS485 module was heavily inspired by an article from the excellent german c't magazin:
Unter Strom - Stromverbrauch analysieren mit Raspi und Smart Meter
In addition to the schematic published a level shifter was added for the RXD input.
This shield was build around the MAX485 module from LC Electronics.
There is an AISLER project if you like to order a PCB.