A battery alarm system

Abstract: The present invention relates to a battery alarm system for raising an alarm on recognition of the reduction of output voltage of a battery (31), wherein an analog output voltage value of a battery (31) is converted to a digital value; the digitalized values are inputted for a plurality of times at a predetermined interval to obtain the average value; and when the average value is smaller than the predetermined threshold, an alarm is raised. By obtaining an average value among voltage values inputted for a plurality of times, an alarm can be raised stably with little influence of the fluctuation of the output voltage of the battery (31).

Description: Background of the Invention The present invention relates to a battery alarm system for monitoring output voltage of a battery used for a portable telephone, etc., and raising an alarm on recognizing the reduction of the output voltage. A portable telephone requires an alarm system for raising an alarm (sound or indicator) to notify the user of the reduction of output voltage of a battery which causes an inoperative condition of the portable telephone. In response to the alarm, the user determines whether he will stop using the portable telephone or take an appropriate action such as charging the battery. A precise and stable alarm should be raised to make a correct determination. Figure 1 shows a configuration of a conventional battery alarm system. In Figure 1, a voltage detector IC 32 and a system power source 35 are connected to the output terminal of a battery 31. The output of the voltage detector IC 32 is applied to a CPU 33. The CPU 33 and a program storage 34 are provided with electric power by the system power source 35, and the CPU 33 performs a predetermined process stored in the program storage 34. In the above described configuration, the voltage detector IC 32 detects output voltage of the battery 31, compares the obtained value with a predetermined threshold Vth, and notifies the CPU 33 of the result. The CPU 33 determines the alarm state when it recognizes that the output voltage of the battery 31 is lower than the threshold Vth. Then, it causes an alarm to be sounded with a buzzer 36 and a blinking alarm, etc. to be made on a display device. In a conventional battery alarm system, however, the generation of an alarm greatly depends on the capability of a voltage detector IC 32. That is, the detector notifies a CPU 33 of information of "the alarm state" and "the normal state" changeably within a short time when the output voltage of the battery 31 is unstable and fluctuating, thus generating an alarm unstably. Besides, in a conventional system, a threshold Vth of the voltage detector IC 32 is fixed to a determined value. Therefore, when an alarm raising value of voltage must be modified, another voltage detector IC having another threshold should replace the first detector, thus the system gets inoperative during an emergency modification. US-A-4 633 418 shows features corresponding to those of the preamble of claim 1. US-A-4 929 931 shows a battery monitor which compares measured voltage to nominal levels, and determines discharge rates. Summary of the Invention An object of the present invention is to provide a battery alarm system for determining the alarm state correctly even when output voltage of a battery is unstable, and for easily modifying the alarm raising value of voltage. The present invention provides a battery alarm system as set out in claim 1. Preferred features are set out in dependent claims. Brief Description of the Drawings Figure 1 shows a configuration of a conventional battery alarm system; Figure 2 shows a block diagram of the principle of the present invention; Figure 3 shows a configuration of an embodiment; and Figure 4 shows a flowchart for explaining the operation of the above described embodiment. Embodiments Figure 2 shows a block diagram for explaining the principle of the present invention. In Figure 2, a battery alarm system generates an alarm on recognizing the reduction of output voltage of a battery 31, and comprises an analog/digital (A/D) converter 11, a storage 12, a controller 13, and an alarm generator 14. The analog/digital converter 11 converts an analog value of output voltage of the battery 31 to a digital value. The storage 12 stores a threshold based on which output voltage of said battery is judged whether or not it is low enough to raising an alarm (referred to as the alarm state). The controller 13 obtains an average value of digitalized output voltage values after inputted for a plurality of times at a predetermined interval, compares the average value with the threshold, recognizes the alarm state when the average value is smaller than the threshold, and then raises an alarm from the alarm generating means. The alarm generator 14 comprises, for example, a buzzer, a lamp, etc. for raising an alarm (sound and indicator) according to the instruction of the controller 13. An analog value of output voltage of a battery 31 is converted to a digital value by the analog/digital converter 11. The digital value of output voltage is read into the controller 13 for a plurality of times at a predetermined interval (within a short time), and then the average value is obtained. By converting an analog value to a digital value and obtaining an average value as described above, the influence of voltage fluctuation of a battery within a short time can be reduced, and a stable value of output voltage can be obtained by the controller 13. As the controller 13 determines the alarm state after comparing the stable value of output voltage (average value) with the threshold stored in the storage 12, an alarm system can constantly raise an alarm stably with little influence of output voltage fluctuation of the battery 31. An embodiment of the present invention is explained below in association with drawings. Figure 3 shows a configuration of an embodiment of the present invention. In Figure 3, explanation is skipped (replaced with equal numbers) for the parts corresponding to those shown in Figure 1. An analog/digital converter (A/D converter) 21 is connected to the output terminal of a battery 31, and the output (a digital value) is applied to a CPU 22. The CPU 22 executes the following predetermined processes according to the program stored in a memory 23. The converting operation of the analog/digital converter 21 is performed under the control of the CPU 22. Next, the process by a CPU 22, as a controller, is explained based on the flowchart shown in Figure 4. When a system power source 35 is turned on, the process starts with the confirmation of ON or OFF of the power source 35 (step S1). If OFF, the process is terminated. If ON, a variable n representing the occurrence number is set to 0, and a variable m representing the value of output voltage of the battery 31 is set to 0 (step S2). Then, the analog/digital converter 21 starts converting an analog value to a digital value (step S3), and the system waits for the completion of the conversion (step S4). After the conversion, a converted value (digital value) is stored (step S5); the value 1 is added to the variable n, and the converted value is added to the variable m (step S6). Next, it is determined whether or not the variable n is equal to the predetermined value N (occurrence number) (step S7); if no, control is returned to step S3 and the process is repeated until N equals n (steps S3 - S7). In step S7, when N=n, the read value m is divided by the occurrence number N for obtaining the average value m/N because the value m indicates an addition of N converted values of output voltage of the battery 31 (step S8). Then, the threshold Vth stored in the memory 23 is compared with the average value m/N (step S9). If the average value m/N is larger than the threshold Vth, the battery is judged as in the normal condition, and an alarm flag is set OFF (step S10). If the threshold Vth is larger than the average m/N, the battery is judged as in the alarm state, and the alarm flag is set ON (step S11). Next, the setting of the alarm flag is checked: if ON, a buzzer 36 sounds an alarm or a lamp starts blinking as an alarm indicator (step S13); if OFF, an alarm is not raised and control is returned to step S1. When control is returned to step S1, the processes S1 - S13 are repeated until the system power supply 35 is turned off. Though the occurrence number N can be set optionally, correct determination can be made with N set to an optimum value. That is, the larger the value of N, the more effectively the fluctuation of output voltage can be averaged, but the poorer the response to the abrupt voltage reduction is. If the memory 23 comprises an EEPROM for storing a program, the threshold Vth predetermined in the program can be modified and the alarm raising value of output voltage is easily changed. In calculating an average value of the output voltage value (in digital value) of a battery, the above described output voltage value is inputted for a plurality of times at a predetermined interval. For example, when the input time is assumed to be t1, t2, t3, t4, ... (a value is inputted for a plurality of times at a predetermined interval as described above), an average value between t1 - t4 is obtained first in the above described embodiment, and then an average value between t9 - t11 is obtained, thus obtaining average values in a time divisional manner without overlapping time intervals. However, average values can be obtained in another way where an average value is obtained first between t1 - t4, then between t2 - t5, and next between t3 - t6, thus obtaining average values by overlapping part of time intervals in which the average is obtained. This overlapping way is more useful to obtain the output voltage value of a battery. Since the battery voltage fluctuates a little with the variation of environmental temperature, a temperature sensor can be provided to adjust the above described threshold Vth according to the detected temperature. A threshold Vth can be adjusted easily in the present invention because it can be performed digitally. The present invention provides a system for converting an analog value of output voltage of a battery to a digital value, storing the digital value, obtaining an average value after reading the digital values for a plurality of times at a predetermined interval, and raising an alarm stably and constantly with little influence of voltage fluctuation. Additionally, the present invention admits modifying a threshold by rewriting a program stored in the storage, so the alarm raising value of output voltage can be appropriately modified optionally.

Claims: A battery alarm system for raising an alarm from an alarm generating means (14, 36) on recognizing the reduction of output voltage of a battery (31) comprising: an analog/digital converting means (11, 21) for converting an analog output value of said battery to a digital value, a storing means (12, 23) for storing a threshold to enable recognition of a reduction of output voltage of said battery to a level low enough to raise an alarm, and a control means (13, 22) for raising an alarm from said alarm generating means according to said digital output voltage value, characterised in that said control means is for obtaining an average output voltage value from a plurality of samples taken at a predetermined interval, of said digital output voltage values, comparing said average value with said threshold, recognizing the alarm state when said average value is smaller than said threshold, and then raising an alarm from said alarm generating means. A battery alarm system according to claim 1, wherein said storing means is an EEPROM. A battery alarm system according to claim 1, wherein said alarm generating means sounds an alarm with a buzzer. A battery alarm system according to Claim 1, wherein said alarm generating means comprises an indicator for notifying a user of an alarm. A battery alarm system according to Claim 1, wherein said control means obtains average values with part of time intervals overlapped.

Inventors: KOMATSUDA SEIJI, KOMATSUDA, SEIJI
Applicants: FUJITSU LTD, FUJITSU LIMITED
Application year: 1991
Main classification: H04M1
IPC codes: H04M1, H02J7, G01R31