DMX512 control of low voltage switch closure devices (such as slide projectors and fog machines) is made possible with these low voltage DMX Relay Packs. Doug Fleenor Design DMX Relay Packs use dry contact air-gap relays. These relays have advantages and disadvantages over the solid state relays found in dimmer packs. Air-gap relays do not leak current, but due to their mechanical design have a finite life span.