  This paper introduces a series of papers aiming to study the dozens of low
mass eclipsing binaries (EBLM), with F, G, K primaries, that have been
discovered in the course of the WASP survey. Our objects are mostly single-line
binaries whose eclipses have been detected by WASP and were initially followed
up as potential planetary transit candidates. These have bright primaries,
which facilitates spectroscopic observations during transit and allows the
study of the spin-orbit distribution of F, G, K+M eclipsing binaries through
the Rossiter-McLaughlin effect. Here we report on the spin-orbit angle of
WASP-30b, a transiting brown dwarf, and improve its orbital parameters. We also
present the mass, radius, spin-orbit angle and orbital parameters of a new
eclipsing binary, J1219-39b (1SWAPJ121921.03-395125.6, TYC 7760-484-1), which,
with a mass of 95 +/- 2 Mjup, is close to the limit between brown dwarfs and
stars. We find that both objects orbit in planes that appear aligned with their
primaries' equatorial planes. Neither primaries are synchronous. J1219-39b has
a modestly eccentric orbit and is in agreement with the theoretical
mass--radius relationship, whereas WASP-30b lies above it.
