Fluorescence detector for Extensive Air Showers in the region of 10¹⁷ – 10²¹ eV

We present preliminary results on the operation of a fluorescence detector for ultra energetic cosmic rays. This detector was designed to measure the energy of primary particles that generate extensive air showers in the region of 10¹⁷ – 10²¹ eV. We also discuss the main features of the electronic cameras that will be used by the fluorescence detectors of the Kosmotepetl and Pierre Auger projects and present results of simulations appropriate to these cameras.