  On-chip actuation and readout of mechanical motion is key to characterize
mechanical resonators and exploit them for new applications. We capacitively
couple a silicon nitride membrane to an off resonant radio-frequency cavity
formed by a lumped element circuit. Despite a low cavity quality factor
(Q$_\mathrm{E}\approx$ 7.4) and off resonant, room temperature operation, we
are able to parametrize several mechanical modes and estimate their
optomechanical coupling strengths. This enables real-time measurements of the
membrane's driven motion and fast characterization without requiring a
superconducting cavity, thereby eliminating the need for cryogenic cooling.
Finally, we observe optomechanically induced transparency and absorption,
crucial for a number of applications including sensitive metrology, ground
state cooling of mechanical motion and slowing of light.
