Without knowing the details but if you need a low current operating device to pick up a relay from 5v then the Fet 2n7000 should do it easily.
Search here for 2n7000 should bring up some results.
It is possible your BOB has a opto isolator on the output which will not pick up a relay due to insufficient current capability.
Here is one http://www.cnczone.com/forums/genera...64477-cnc.html
Al.