Electromechanical watch capable of contactless communication with a communication device

A method for contactless communication between a timepiece (50) and an external communication device (100), the communication method comprising, in order for the timepiece to receive encoded data in bit form in a magnetic signal (70) transmitted by the external communication device, the following steps of:

• positioning the timepiece relative to the external communication device such that an external magnetic field (HExt) emitted by the device, to form the magnetic signal, propagates in the stator of the stepper motor mainly in a direction parallel to a general plane of the stator and substantially orthogonal to a direction (14) of alignment of the two isthmi (12a, 12b) of the stator;
• receiving, by the communication means of the timepiece, a signal for activating a communication mode;
• then
• generating at least one preliminary electrical pulse (84) supplied to the coil (18) of the stepper motor (2);
• and receiving, by the external communication device (100), at least one magnetic synchronisation pulse generated by said at least one preliminary electrical pulse circulating in the coil;
• detecting, using the external communication device, a specific time position in at least one magnetic synchronisation pulse of said at least one magnetic synchronisation pulse, in particular a rising edge or a middle time value of at least one of the magnetic synchronisation pulses;
• then
• generating electrical detection pulses (82) supplied to the coil with a given pulse frequency and in phase with said at least one synchronisation pulse (84);
• and simultaneously transmitting the magnetic signal (70), using the external communication device, the encoded data having an encoding frequency substantially equal to the pulse frequency and the magnetic signal (70) being transmitted in such a way that the high and low levels of the external magnetic field (HExt), corresponding to the ‘1’ and ‘0’ bits of the encoded data, are synchronised with the electrical detection pulses (82) so that each high level of the external magnetic field, corresponding to a ‘1’ bit, is present in the stator (4) of the stepper motor during a corresponding detection pulse and so that each low level of the external magnetic field, corresponding to a ‘0’ bit, occurs during a corresponding detection pulse;
• measuring, using the detection circuit (24) of the communication means of the timepiece (50), said at least one parameter (TM) for each of the electrical detection pulses (82) occurring during the reception of said encoded data in the magnetic signal (70);
• processing, using the processing circuit (36) of said communication means, said at least one parameter measured for each electrical detection pulse (82) so as to determine, depending on said at least one parameter measured, whether the electrical detection pulse occurred during a high or low level of the external magnetic field and thus to determine the corresponding bit value, either ‘1’ or ‘0’, in the magnetic signal, so as to obtain a bit sequence corresponding to the encoded data in the magnetic signal.