Device for the entry of data to be placed on a touch panel of a terminal, corresponding method and entry system

A system of data entry comprising:

• a touch panel of a terminal;
• and
• a data-entry device configured to be placed on said touch panel,
• said touch panel being capacitive, comprising electrodes in rows and columns forming a matrix of electrodes comprising nodes and being managed by a control unit configured to carry out cycles of capacitive scanning and measurement of variance of capacitance of the nodes relative to reference values, detect meaningful touches on the touch panel as a function of the measured variations in capacitance and recalibrate the reference values as a function of the measured variations in capacitance,
• said data-entry device comprising:
• a generally parallelepiped-shaped plate comprising a generally flat lower face, for placing the device on the touch panel;
• and an upper face comprising a keypad-forming matrix of entry zones, the entry zones having a thickness configured to enable a detection of a finger by the touch panel when the device is placed on the touch panel;
• at least one flat, contact pad that is electrically conductive and fixedly attached to the lower face, said at least one contact pad having a capacitance enabling the at least one contact pad to be detected as a meaningful touch;
• and
• a network of conductive tracks stretching over at least a part of the upper face and being electrically connected to said at least one contact pad, the network of conductive tracks having a capacitance such that it is not detected as exerting a meaningful touch, and occupying a surface area that is greater than the surface area occupied by said at least one contact pad and sufficient so that, during the capacitive scanning cycles, the network of conductive tracks interacts with several nodes of the matrix of electrodes in the form of charges that go back and forth in the network of conductive tracks, as well as between said at least one contact pad and the network of conductive tracks, thus changing the charge of the network of conductive tracks and of said at least one contact pad and, therefore, for the nodes of the matrix of electrodes, situated facing the network of conductive tracks and said at least one conductive pad, called concerned nodes, the control unit measures the variations in capacitance that are not fixed on successive cycles and decides therefore not to carry out a recalibration of the reference values for the concerned nodes.