We discuss the design of a simple experiment that reproduces the operation of the Michelson stellar interferometer. The emission of stellar sources has been simulated using light emerging from circular end-faces of step-index polymer optical fibers and from diffuse reflections of laser beams. Interference fringes have been acquired using a digital camera, coupled to a telescope obscured by a double aperture lid. The experiment is analogous to the classical determination of stellar sizes by Michelson and can be used during the day. Using this experimental set-up, we can determine the size of extended sources, located at a distance of about 75 m from our telescope, with errors less than 25%.