Patent ID: 6563422
Filing Date: 2003-05-13
Classification: G04G,G08B

Abstract:
A non acoustic alarm device, intended to be fitted to a portable device worn next to the body for use in a timepiece or a portable telephone, the non acoustic alarm device including:a case; a moving mass within the case intended to transmit vibrations thereto; a coil electromagnetically coupled to said moving mass to cause said moving mass to oscillate, wherein said coil and said moving mass form a coil-moving mass unit; and an excitation circuit of said coil, wherein said non acoustic alarm device further includes means for measuring the instantaneous oscillation frequency of the coil-moving mass unit during the period of oscillation in progress, as well as means for generating, during the next period of oscillation, a series of excitation pulses for said coil, said series of excitation pulses having characteristics that are a function of the measurement of said instantaneous oscillation frequency, said moving mass oscillating freely between two successive excitation pulses so as to allow a measurement of said instantaneous oscillating frequency of the coil-moving mass unit.