The best RealSense camera choice for the Joule is the ZR300. The R200 may also work but is not officially supported to do so. The SR300 is not validated to work with the Joule, sadly, due to incompatible architectures. This has been stated to be the case by two Intel support staff members, Sergio and Pedro, in replies to other peoples' questions about SR300 compatibility.
Sergio explains the different power voltages in this post.