This paper presents collision avoidance implementation on a Crazyflie 2.1 nano quadcopter featuring modular
architecture. Autonomous navigation was implemented using
special decks. One of those decks can accurately measure distance to surrounding objects in four directions. The second deck can measure the distance to the surface below the quad and pick up the coordinates onboard. A simple algorithm was developed to avoid collision with single obstacles; the algorithm has since been tested on an actual nano quadcopter. The paper presents the results of that test. According to the results, the tested equipment is suitable for indoor collision avoidance implementation on autonomous quadcopters.