  The formation of sandpiles is a subject if interest in the field of granular
matter, but most experiments are unable to control the kinetic energy of the
grains added to the apex of the growing pile. In this short article, we
describe an opto-mechanical system to grow granular piles by adding sand from a
fixed distance above the apex of the pile. To achieve that, we use a laser beam
that detects the position of the apex and, as the pile grows, sends a feedback
signal to a mechanical device able to control the height of the sand delivey
system above the pile.
