Abstract:
A car speed alarm system is installed in a vehicle and has a modulation module and a demodulation module. The modulation module sends a car speed signal to cars behind when the car is decelerating. The cars behind use their demodulation module to read the transmitted car speed signal and notify their drivers, so that the drivers know how and when to reduce their speeds.

Description:
BACKGROUND OF THE INVENTION  
       [0001]    1. Field of the Invention 
         [0002]    The invention relates to an alarm system and, in particular, to a car speed alarm system. 
         [0003]    2. Description of Related Art 
         [0004]    Due to the popularity of cars, there are more people driving their own cars. A direct consequence is that there are more car accidents. Among all accidents, collisions from behind are the most common type. 
         [0005]    One primary cause of collisions from behind is either the distance between cars is too short or the car speed is too fast. If a car in the front suddenly decelerates, the driver of the car directly behind often does not have sufficient time to react, resulting in collisions. To reduce the above-mentioned car accident rate, people often put a set of distance check signs at appropriate places (e.g., “0 m,” “50 m,” “100 m,” and “200 m” signs at 0 m, 50 m, 100 m, and 200 m). Alternatively, several car distance alarm lines are drawn at equal intervals on each lane. These methods help drivers keep appropriate distances from the cars in front of them. This can prevent some of the collisions from behind. However, the car distance check sips or car distance alarm lines are installed or drawn at fixed or specific places. Car drivers cannot check the distances at any time. 
         [0006]    To notify the driver of the car behind, each car is provided with several brake lights. When a driver steps on the brake, the brake lights are turned on so that drivers of the cars behind can slow down their speeds appropriately. However, the existing brake lights have only ON and OFF states, without providing any additional information. For example, the brake lights cannot provide the car speed information to the drivers behind. Thus, even if the drivers of the cars behind know that the car in the front is decelerating, the collision may still happen because he does not know about how large the deceleration is. 
       SUMMARY OF THE INVENTION  
       [0007]    To solve the problem that existing brake lights do not provide car speed information to the cars behind and may result in collisions, the objective of the invention provides a car speed alarm system installed in the vehicle. The car speed alarm system has a modulation module and a demodulation module. 
         [0008]    The modulation module outputs the car speed to the cars behind, and comprises 
         [0009]    a brake sensor to detect brake actions; 
         [0010]    a speed sensor to detect the car speed; 
         [0011]    a microprocessor having input terminals being connected with the brake sensor and the speed sensor, wherein the microprocessor is triggered by the brake sensor and reads the car speed during the brake, and the car speed is converted into a binary signal for output; and 
         [0012]    a brake light connected with the output terminals of the microprocessor and generating a binary light signal with varying brightness according to the binary signal. 
         [0013]    The demodulation module analyzes the binary light signal sent from the modulation module, and comprises 
         [0014]    a sensing unit receiving the binary light signal from the brake light of the car in the front and the environmental background light signal; 
         [0015]    a processing unit connected with the output terminal of the sensing unit to receive the output signal from the sensing unit and determining the brightness variation of the brake light of the car in the front; and 
         [0016]    an outputting unit connected with the output terminal of the processing unit to receive and output the output signal of the processing unit. 
         [0017]    The car in the front can transmit via the modulation module car speed information to the demodulation module of the car behind. The driver of the car behind thus knows the car speed of the car in the front as it decelerates. The driver of the car behind can appropriately adjust his car speed and distance, thereby avoiding collision from behind. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
         [0018]      FIG. 1  is an operational view of a car speed alarm system in accordance with the present invention; 
           [0019]      FIG. 2  is a system block diagram of a modulation module of the car speed alarm system in accordance with the present invention; 
           [0020]      FIG. 3  is a system block diagram of a demodulation module of the car speed alarm system in accordance with the present invention; and 
           [0021]      FIG. 4  is a schematic view of the binary signal used in the invention. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0022]    With reference to  FIG. 1 , a car speed alarm system in accordance with the present invention is installed in a car  30 . The car speed alarm system includes a modulation module  10  and a demodulation module  20 . 
         [0023]    With further reference to  FIG. 2 , the modulation module  10  includes a brake sensor  12 , a speed sensor  14 , a microprocessor  16 , a switch  17 , a power supply  18  and a brake light  19 . The output terminals of the brake sensor  12  and the speed sensor  14  are connected to the microprocessor  16 . The output terminal of the microprocessor  16  is connected to the control terminal of the switch  17 . The input terminal of the switch  17  is connected to the power supply  18 . The output terminal of the switch  17  is connected to the brake light  19 . The brake light  19  is disposed at the rear part of the car  30  in order to send signals to the cars behind. 
         [0024]    With further reference to  FIG. 3 , the demodulation module  20  includes a sensing unit  22 , a processing unit  24  and an outputting unit  26 . The output terminal of the sensing unit  22  is connected to the processing unit  24 . The output terminal of the processing unit  24  is connected to the outputting unit  26 . Besides, the sensing unit  22  has to be disposed in the front part of the car  30  for receiving signals from the cars ahead of it. 
         [0025]    The processing unit  24  further includes one comparison circuit  242 , two rectifiers  244 , two signal amplifiers  246 , and one output processor  248 . The two input terminals of the comparison circuit  242  are first connected in series with one of the rectifiers  244 , respectively, then connected to one of the signal amplifiers  246 . The output terminal of the comparison circuit  242  is connected to the output processor  248 . 
         [0026]    Moreover, the sensing unit  22  also includes a car light sensor  222  and an environmental light sensor  224 . The output terminal of the car light sensor  222  is connected with the signal amplifier  246  that is connected to the positive input terminal of the comparison circuit  242 . The output terminal of the environmental light sensor  224  is connected with the signal amplifier  246  that is connected to the negative input terminal of the comparison circuit  242 . 
         [0027]    Suppose two cars are provided with the car speed alarm systems, or the car in the front is installed with the disclosed modulation module  10  and the car behind is installed with the disclosed demodulation module  20 . When the front car is braking, the brake sensor  12  outputs a triggering signal to the microprocessor  16 . The microprocessor  16  uses the speed sensor  14  to read the current car speed of the front car. Afterwards, the microprocessor  16  converts the car speed into a binary signal with multiple bits. The binary signal is used to control the switch  17 , so that the switch  17  is ON or OFF accordingly. When the bit of the binary signal is “1,” the switch  17  is turned on. When the bit is “0,” the switch  17  is turned off. In the case when the switch  17  is turned on, the brake light  19  and the power supply  18  are disconnected. Therefore, the brake light  19  is off. When the switch  17  is turned off, the brake light  19  and the power supply  18  are electrically connected so that the brake light  19  is turned on. 
         [0028]    The car light sensor  222  and the environmental light sensor  224  of the rear car keep receiving brightness change of the surrounding light. The signals received by the car light sensor  222  and the environmental light sensor  224  go through the signal amplifier  246  and the rectifier  244 . The results are fed into the comparison circuit  242  for a comparison. When the brake light  19  of the front car is on, the light signal strength received by the car light sensor  222  of the rear car is larger than the environmental background light strength received by the environmental light sensor  224 . The comparison circuit  242  of the rear car outputs a high-voltage signal. On the other hand, if the brake light  19  of the front car is off, the light signal strength received by the car light sensor  222  of the rear car is smaller than the environmental background light strength received by the environmental light sensor  224 . The comparison circuit  242  outputs a low-voltage signal. The comparison circuit  242  of the rear car outputs the result to the output processor  248 . The output processor  248  converts and outputs the output data of the comparison circuit  242  to the outputting unit  26  for notifying the driver thereof. 
         [0029]    For example, suppose the front car is braking while running at a speed of 100 km/hr. The binary signal output from the microprocessor  16  to the switch  17  is “01100100.” Therefore, the switch  17  of the front car turns on and off according to the binary signal, with “0” representing OFF and “1” representing ON of the switch  17 . The brake light  19  of the front car is thus on and off, as shown in  FIG. 4 . The sensing unit  22  of the rear car receives the light signal “01100100” sent from the brake light  19  of the front car. The processing unit  24  converts the light signal into a signal acceptable by the outputting unit  26 . The converted signal is then output to notify the driver of the rear car. Moreover, the switch  17  can be transistor, such as a metal oxide semiconductor field effective transistor (MOSFET). In this case, the gate of the MOSFET is connected to the output terminal of the microprocessor  16 . Its source is connected to the power supply  18 . Its drain is connected to the brake light  19 . Thus, when the microprocessor  16  outputs a high-voltage signal, the transistor is conductive so that the electrical power of the power supply  18  is output to the brake light  19 . 
         [0030]    The outputting unit  26  is a display or voice player for outputting the output signal of the processing unit  24  and alerting the driver of the rear car. In the previous example, the outputting unit  26  notifies the driver of the rear car about the information of 100 km/hr by LED display or playing voices. 
         [0031]    To avoid misjudgment due to the interference of other environmental light noises also with varying brightness and to prevent the driver of the rear car from being disturbed by the flashing brake light  19  of the front car, the transmission rate of the output terminal of the microprocessor  16  can be tuned so that the brake light  19  transmits information at a fixed flashing rate, such as 9600 bit/sec. In that case, each bit is transmitted within about 1 ms (T 2  in  FIG. 4 ). Because of visual persistence of human eyes, the driver of the rear is not disturbed by the brake light  29  of the front car flashing at such a high rate. Moreover, the stable transmission rate also enables the demodulation module  20  to distinguish the signal from the brake light  19  from the variation in the environmental light. Consequently, the output processor  248  of the rear car is free from misjudgment. 
         [0032]    Besides, the delay time for a normal car driver to execute braking is usually greater than 1 second (T 1 +T 3 ). When the car driver starts to step on the brake, a braking signal is transmitted at the above-mentioned rate to the rear car. The time (T 3 ) required for the signal transmission is about several milliseconds. The output of the comparison circuit  242  of the rear car is a series of high-voltage levels (e.g., signal with the T 1  interval). To prevent the output processor  248  from misjudging on the signal with the T 1  interval, the front car can use a fixed and fast transmission rate (shortening T 2 ). This can effectively distinguish the car speed signal from the quick brake light flashing due to the intermittent braking by the driver of the front car. As shown in  FIG. 4 , the interval of the intermittent braking by the driver of the front car is T 1 . T 1  is general is much larger than T 2 . Therefore, the car light sensor  222  of the rear car can easily tell them apart. 
         [0033]    In summary, the invention enables the brake light  19  of a car to transmit its speed to the cars behind. The driver of the car behind is not only notified about the deceleration of the car in the front but also knows about its current speed. The driver of the rear car can thus appropriately adjust his own speed in order to keep a safe distance from the front car, thereby preventing a possible collision. 
         [0034]    While the invention has been described by way of example and in terms of the preferred embodiment, it is to be understood that the invention is not limited to the disclosed embodiments. To the contrary, it is intended to cover various modifications and similar arrangements as would be apparent to those skilled in the art. Therefore, the scope of the appended claims should be accorded the broadest interpretation so as to encompass all such modifications and similar arrangements.