The present invention concerns an identification device of a manual action on a surface performed by a finger and, more specifically, it concerns such device comprising a set of sensors which are each actuable by the finger of a user so as to create a variation of an electrical quantity. Such device may be used in horological applications, such as a wrist-watch comprising a recognition device for recognising characters drawn manually on the glass of the watch. It should however be understood that the invention is not limited to this application.
Watches comprising identification devices such as defined hereabove are already known. The document EP-A-0 165 548 describes an electronic watch comprising a recognition device of characters drawn manually on the glass of a watch. A matrix of photoelectrical sensors is arranged on the bottom surface of the glass. When the user draws a character on the top surface of the glass, the intensity of the light detected by the photoelectrical sensors is modified, which then thus allows the detection of the coordinates of the transcribed character. The written character is then recognised according to the detected coordinates. To do this, the respective coordinates of the lines forming the drawn character are memorised in a memory device. These coordinates are compared to reference coordinates which are also memorised in the memory device so as to find the reference coordinates which are the most similar to the coordinates corresponding to the character written on the glass. When the user draws this character, it often happens that several sensors are activated simultaneously. So as to be capable of determining the coordinates of the drawn character, it is thus necessary to calculate the center of gravity of the group of sensors which are activated at the same time by the user.
The calculation of the center of gravity often presents several inconveniences. On the one hand, the processing of data necessary for taking into account factors such as the diametrical disposition of the actuated sensors, is a complex task which imposes a high burden on the data processing circuit associated to these sensors and which leads to a slow response time of this circuit. On the other hand, the result of this calculation often lacks precision, which leads to recognitions errors of characters written by the user.