Abstract:
A power saving device for a GPS device is to utilize acceleration of gravity sensor to continue detecting the acceleration variation of the GPS device; if an acceleration value is larger than a threshold value, a GPS signal receiver is then started; if the acceleration value is smaller than the threshold value, the GPS signal receiver is then shut. This allows the GPS device to be power saving and not need to facilitate an extra oscillation switch therein to save the production cost.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a GPS device, and more particularly to a power saving device for a GPS device. 
     2. Description of Related Art 
     The upgrading of the manufacturing technology and the functions of an electronic product enable the use of a GPS device to be more popular. There are many types of the GPS device such as a portable GPS device convenient for being used in an individual&#39;s mountain climbing and travel, GPS device combined with a cellular phone and GPS device combined with a vehicle allowing a user to realize his position and the direction of the destination that he wants to go if it is operated in coordination with an electronic map. 
     All general portable GPS devices use a battery to provide electricity. When a GPS receiver is in a normal operation, it is very power consuming. If the GPS device is not moved, it can enter a rather power consuming mode, the power can then be saved so that the use life of the battery can be extended. 
     U.S. Pat. No. 6,774,838 discloses a power saving device and method for a GPS receiver, in which the power saving device allows the GPS receiver to be connected to an oscillation switch and the vibration generated from the moving of the GPS receiver can be utilized to actuate the oscillation switch to turn on the power of the GPS receiver automatically with a power controller. The oscillation switch enables the power controller to turn off the power of the GPS receiver automatically when the GPS receiver is not moved so that the power can be saved. 
     An acceleration of gravity sensor (G-sensor) is installed in a several GPS devices. The G-sensor detects the variation of gravity to measure the acceleration generated from the movement of a body and output a simulated voltage signal. This can provide the data of the acceleration of the body so as to assist the GPS receiver to provide the data of the velocity and the position of the body even in such as a time period that the satellite signals cannot be received or well received when it is in tunnel or is blocked by mountains, trees, buildings and etc. When the G-sensor is under a work voltage of 3.3 volts, the power consumption thereof is 1 mA; this is far less than the one needed for the GPS receiver. 
     SUMMARY OF THE INVENTION 
     For improving a conventional power saving device for a GPS device to allow the production cost to be more saved, the present invention is proposed. 
     The main object of the present invention is to provide a power saving device for a GPS device, enabling the GPS device to have a function of power saving. 
     Another object of the present invention is to provide a power saving device for a GPS device, utilizing a G-sensor installed therein and needing no extra oscillation switch so as to save the production cost. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention can be more fully understood by reference to the following description and accompanying drawings, in which: 
         FIG. 1  is a block diagram of a power saving device for a GPS device of a preferred embodiment according to the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Please refer to  FIG. 1 .  FIG. 1  is a power saving device for a GPS device of a preferred embodiment according to the present invention. The power saving device comprises a GPS receiver  10  electrically connected to a GPS antenna  11 , a power controller  20  and an information record and/or output device  30 , in which a time delay controller  42  is respectively electrically connected to the power controller  20 , the information record and/or output device  30  and the emitter (second pole) of a first transistor  41 . The time delay controller  42  comprises a second transistor  421 , a resistor  422  and a capacitor  423 . The emitter (third pole) of the second transistor  421  is connected to the power source. The collector (second pole) is electrically connected to the power controller  20 . One end of the resistor  422  and one end of the capacitor  423  are grounded, other ends thereof are respectively electrically connected to the collector of the second transistor  421 . The information record and/or output device  30  are connected to the base of the second transistor  421 . The collector (second pole) of the first transistor  41  is electrically connected to the power source and the base (first pole) thereof is electrically connected to the MOT pin of a G-sensor  50 . The G-sensor  50  is communicated with a microprocessor  60  through a transmission interface (SCL, SDA). The microprocessor  60  can set a threshold value triggered by the MOT pin of the G-sensor  50  through this transmission interface. 
     When the power controller  20  detects that the capacitor  423  is charged to have a higher potential, it then starts the GPS receiver  10 ; when the power controller  20  detects that the capacitor  423  has a lower potential, it then closes the GPS receiver  10 . 
     The capacitor  423  has a higher potential at two following conditions:
     (a) When the G-sensor  50  detects that the acceleration value of its movement is beyond the threshold value, it converts the MOT pin to be at a high potential to output a starting signal to allow the first transistor  41  to be communicated, the power is delivered to the power controller  20  and to the capacitor  423  too to cause the capacitor  423  to be charged. Or   (b) When the information record and/or output device  30  is forced to output a low potential, the emitter and the collector of the second transistor  421  are communicated with each other to cause the collector thereof to be at a high potential and the capacitor  423  to be charged. Besides, it also causes the power controller  20  to receive a high potential signal.   

     The capacitor  423  has a lower potential at two following conditions:
     (a) when the G-sensor  50  detects that the acceleration value of its movement is below the threshold value, it converts the MOT pin to be at a low potential and then stop outputting a starting signal to cause the first transistor  41  not to be communicated; no power is delivered to the capacitor  423  to cause the capacitor  423  not to be charged. And   (b) when the information record and/or output device  30  is not forced to output a low potential to cause the emitter and the collector of the second transistor  421  not to be communicated, the collector thereof does not charge the capacitor  423 ;
 
the capacitor  423  is at a low potential by means of the gradual discharge of the resistor  422 .
   

     Selecting different resistor  422  and capacitor  423  can adjust the discharge rate of the capacitor  423 , further control the time that the capacitor  423  is converted to be at a low potential so as to delay the time that the power controller  20  detects that the capacitor  423  has a lower potential to extend the outputting of the signal controlling the GPS receiver  10  from the power controller  20  and further to extend the action time of the GPS receiver  10 . 
     The information record and/or output device  30  according to the present invention has a CPU, capable of processing and operating a position signal transmitted from the GPS receiver  10 , and storing or outputting the processed and operated position signal. After the recording and/or outputting device  30  finishes the data recording and/or outputting action, it can then stop outputting the forced low potential to cause the emitter and the collector of the second transistor  421  not to be communicated. 
     The G-sensor  50  according to the present invention can be an acceleration of gravity sensing chip of serial No. KX984. The microprocessor can be a general microprocessor, such as serial No. 80C51. When the GPS device stops moving, it then enter a power saving mode after a time period; only the G-sensor  50  is left for continuing maintaining power supply and detecting the variation of the acceleration of the GPS device. If the acceleration value is beyond the threshold value, it then starts the GPS receiver. 
     The present invention causes the more power consuming GPS receiver to be automatically turned on and off and only causes the more power saving G-sensor to maintain supplying power to process the detection when the GPS device is stopped, this can greatly save the power. Furthermore, the present invention only utilizes the G-sensor installed in the GPS device to be an element detecting whether the GPS device starts moving or not, other extra oscillation switches need not to be installed, this can rather save the production cost. 
     Additional advantages and modifications will readily occur to those skilled in the art. Therefore, the invention in its broader aspects is not limited to the specific details and representative embodiments shown and described herein. Accordingly, various modifications may be made without departing from the spirit or scope of the general inventive concept as defined by the appended claims and their equivalents.