Abstract: The present invention relates to a method and to a device enabling data to be input, and also to an optical system for detecting the position of an article or a member and suitable for being used (or incorporated) in such a method (or device). The technical field of the invention is that of making keyboards and similar devices enabling manual input of data for processing by a digital computer. The method of the invention for determining the position of an article in a zone uses the steps of structuring a neural network by training, applying data to the input of the structured neural network, the data being the result of converting signals delivered by a plurality of detectors sensitive to illumination of said zone, and determining the position of the article in the zone as a function of at least one data item output by the structured neural network.