1. Field of the Invention
The present invention relates to a hand-held electronic device, such as a mobile phone, a personal digital assistant (PDA), and a digital camera, a household electronic device, or an office electronic device, and more particularly, to an apparatus and method for detecting the free fall of an electronic device to make an internal program (or circuit) of the electronic device enter a safe mode when the electronic device is falling to the ground, thereby preventing damage to the electronic device.
2. Description of the Related Art
In a conventional method and apparatus for detecting the free fall of an electronic device and preventing physical damage to the electronic device due to the shock, a protecting routine against shock is activated when the falling acceleration of the electronic device is sensed and the sensed falling acceleration, which is equal to the reference acceleration of gravity (9.8 m/s2) when the falling begins, is gradually reduced to a positive threshold near 0 and is maintained under that threshold for a predetermined time.
An acceleration sensor, which senses the acceleration of an electronic device, may erroneously determine the reference acceleration of gravity to be greater than 9.8 m/s2 due to a change in internal parameters of the acceleration sensor, or a drift caused by ambient conditions, e.g., a temperature change or a lapse of time. In this case, although the actual falling acceleration of the electronic device is maintained under the threshold for the predetermined time, the acceleration sensor erroneously determines that the falling acceleration is not reduced under the threshold and thus cannot detect the free fall of the electronic device.
FIG. 1 is a graph illustrating a problem of a conventional method of detecting the free fall of an electronic device. Referring to FIG. 1, when an acceleration sensor erroneously senses reference acceleration of gravity to be greater than 9.8 m/s2, an error between the reference acceleration of gravity and the sensed acceleration of gravity is generated, the acceleration sensor determines that the falling acceleration of the electronic device is not reduced to a predetermined threshold ath or less, and thus cannot sense the free fall of the electronic device.
Further, since the predetermined threshold is determined to be approximately equal to 0, the acceleration sensor determines that the electronic device fall freely only when the falling acceleration is approximately equal to 0. Accordingly, the acceleration sensor cannot sense the free fall when the moving direction of the electronic device during a free fall is changed and the falling acceleration is not approximately equal to 0 due to the rotation acceleration of the electronic device.
FIG. 2 is a graph illustrating another problem of the conventional method of detecting the free fall of an electronic device. Referring to FIG. 2, when the electronic device falls freely while rotating and the rotation acceleration of the electronic device is equal to or greater than a predetermined value, the free fall of the electronic device is not sensed since a threshold ath is an approximately equal to 0.
When the falling acceleration of the electronic device temporarily exceeds a threshold within a predetermined length of time due to noise in the acceleration sensor, the length of time that the falling acceleration is maintained is less than the predetermined length of time. Thus, although the electronic device falls freely, the free fall of the electronic device is not detected since the falling acceleration is considered as not being maintained for the predetermined length of time.
FIG. 3 is a graph illustrating yet another problem of the conventional method of detecting the free fall of an electronic device. Referring to FIG. 3, when the falling acceleration of the electronic device is temporarily greater than a threshold ath within a predetermined length of time Tth due to noise in an acceleration sensor, the length of time Tf for which the falling acceleration is maintained smaller than the threshold ath is less than the predetermined length of time Tth. Therefore, the length of time when the falling acceleration is maintained is initialized to 0, thereby preventing the free fall of the electronic device from being detected.