A motorized rotary drum supported on a motor housing bears a plurality of yarn loops wound thereon, such loops being adapted to be unwound upon request from a downstream machine. A yarn-unwinding sensor comprises light-emitting elements and light-receiving elements both of which are integral with the motor housing. Light-guiding elements which are integral with the drum guide the light from the light-emitting elements to a window which is defined on the rotary drum in a position such that it is repeatedly engaged by the yarn during its rotary unwinding motion, and vice versa. A reflecting surface reflects the light coming out of the window back towards the window. Light-deviating elements which are integral with the motor housing deviate the light coming back from the window towards the light-receiving elements. The unwinding of a yarn loop from the drum is determined on the basis of the variation of light resulting from the yarn transiting on the window.

A device for feeding yarn to a textile machine, including a main body defining an entry portion and an exit portion for yarn; a rotatable drum for winding the yarn originating from the entry portion and a motor connected to the drum for rotating the drum; a control member active at least on the motor to regulate its torque and velocity; exit portion being selectively switchable between a first configuration in which it defines a free exit section for the yarn, through which the exiting yarn defines a closed path about a rotation axis of the drum, and a second configuration in which it defines a limited exit section, through which the exiting yarn defines an open path.