OI optocoupler cards: Galvanic isolation of digital signals - Maisach/Munich/Germany. With the electrically isolated optocoupler boards OI16, OI16-PC and OI104 from BMC Messsysteme GmbH (bmcm) digital signals can be received or set without interferences. If there is no electro-conductive contact between two circuits, we are talking about galvanic or electrical isolation. Amongst others it is required for safety reasons, to separate potentials or to prevent hum loops as well as electromagnetic interferences. If galvanic isolation is accomplished by optocouplers, digital signals can be transmitted fast and without interferences in an optical way.