An electromechanical system to follow the position of the sun was designed and built at the Solar Evaluation Laboratory of the Technical University Federico Santa Maria (UTFSM) in Valparaiso. It allows the automatic measurement of direct solar radiation with a pyrheliometer. It operates automatically, guided by a closed loop servo system. A four-quadrant photo detector senses the position of the sun and two small DC motors move the instrument platform keeping the sun's image at the center of the four-quadrant photo detectors. Under cloudy conditions, when the sun is not visible, a computing program calculates the position of the sun and takes control of the movement, until the detector can sense the sun again. The constructed system was tested in the climatic conditions of the city of Valparaiso, Chile. The presented tracker proves the effective work of a simple and cheap mechanism, which can be adapted to also work with larger following installations like solar cell panels, concentrators, etc. (C) 2003 Elsevier Ltd. All rights reserved.