Abstract:
The invention is an easy-to-assemble LED display driven by a simple circuit for any graphics and text by utilizing a plurality of LED display elements with built-in resistors directly installed on a display with power to light up the LED elements and display texts or graphics. This invention, in particular, allows the user compose different texts or graphics by arranging at will the positions of the LED display elements with built-in resistors on a specific circuit.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of Invention 
     The invention relates to an LED display and, in particular, to an easy-to-assemble LED display whose LED display element utilizes multiple built-in resistors and can be directly installed onto a display module with power to display texts or graphics. 
     2. Background of the Invention 
     The lighting methods of the LED displays of the prior art can be categorized into two classes: one is the dynamic impulse scanning and the other is the static electrical current driving. Both these two driving methods can achieve the goal of instantaneously changing graphics and texts. However, the driving control circuits are complicated and expensive. Thus, they are not practical when only simple graphics or texts are to displayed and are not changed very often. 
     Another LED display on the market is realized by imbedding the LEDs onto a display module with fixed texts or graphics, connecting the LEDs with a circuit, and putting on resistors according to the driving voltage. Nevertheless, this application is not flexible and lacks of diversification, it does not meet the need for more varieties of models in limited amount. 
     Owing to the material and processing, current LEDs have different levels of luminosity and colors; under a certain electrical current, they produce different forward biases because of different internal resistance. The present invention connects LEDs with different resistance with built-in resistors with different resistance in series. In this way, the impedance of each LED display element is about the same and the sum of the potential differences of all the LED display elements on the circuit are roughly equal to the voltage of the power supply when they are driven by a specific current. The built-in resistors and the number of the LED display elements on the circuit should be modified according to the power supply voltage to optimize the gain of tight emission. 
     In observation of the imperfection of the LED displays of prior an, the inventor did a thorough research and finally presented this easy-to-assemble LED display for any graphics and text that can be driven by simple circuits. 
     SUMMARY OF THE INVENTION 
     The present invention provides an easy-to-assemble LED display for any graphics and text that is light and can be driven by a simple circuit. Multiple matrix display modules can be combined in a way that satisfies the user&#39;s need. 
     Furthermore, the instant invention provides an easy-to-assemble LED display for any graphics and text, wherein the LED display element is a package of LED display elements with different resistance connecting to different resistors in series in such a way that the resistance of each LED is roughly the same. 
     Yet, the invention provides an easy-to-assemble LED display for any graphics and text so that the user can assemble the LED display elements into needed graphics to replace for the signboards made with neon or fluorescent lamps or any signpost with light used on the market, so as to achieve the goal of saving the energy and lowering the cost. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The drawings disclose an illustrative embodiment of the present invention which serves to exemplify the various advantages and objects hereof, and are as follows: 
     FIG. 1 is a three-dimensional view of a 7×8 matrix module according to the invention; 
     FIG. 2 is a basic driving circuit of the invention; 
     FIG. 3 is a cross section of an LED display element with built-in resistors according to the invention; 
     FIG. 4 is another type of LED display element; 
     FIG. 5A is an actual circuit of a display composed of multiple matrix modules driven by alternative currents according to the invention; 
     FIG. 5B is an actual circuit of a display composed of multiple matrix module driven by direct currents according to the invention; 
     FIG. 6 is an illustrative diagram of the invention using a spring chip switch; 
     FIG. 7 is a functional plot of the invention with four 7×8 matrix modules; and 
     FIG. 8 is an actual circuit of a display composed of multiple linear modules driven by direct currents according to the invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Please refer to FIG.  1 . The circuit of the display board module is made on a printed circuit board into a matrix base  51  enclosed by an upper cover  52  and a lower cover  53 . The upper cover has a 7×8 matrix of holes  521  in alignment with the slots  511  on the base  51 . Plug LED display elements  10  into the matrix holes  5231  according to the text or graphics to be displayed, and plug resistors R with comparable impedance to the LED display elements  10 . The resistors R can be plugged into the holes on the base beforehand. 
     Please refer to FIG. 2, which is a basic driving circuit of the invention. The power supply has a voltage VDC, the LED display elements on the circuit are  101 ,  102 , . . .  10 n, with forward biases Vf 1 , Vf 2 , . . . Vfn and internal resistors  151 ,  152 , . . .  15 n with resistance R 1 , R 2 , . . . Rn, respectively. 
     The driving voltage VDC is divided into n voltage drops with each equal to VDC/n. VDC/n&gt;Vfmax, where Vfmax is the maximal forward bias of various LEDs used in the display module. For example, the driving current is If, then each LED with the forward bias Vf needs to be connected to a resistor with resistance R=(VDC/n−Vf)/If. In this way, the LED display element connecting to the resistor can be replaced in the display module at one&#39;s will. Thus, when the driving current is set to be I, the total impedance of the driving circuit is            V   DC     I     ,                          
     the internal resistance of the LEDs are            V   f1     I     ,                                    V   f2     I                   …                       V     f                 n       I     .                             
     We have, according to theory,            V   DC       n                 I       ≈         V   f1     I     +     R   1       ≈         V   f2     I     +       R   2                   …       ≈         V   fn     I     +     R   n                              
     where “≈” means equal or approximately equal. Therefore, different LEDs  111 - 11 n can be packaged into the LED display elements  10  with equal or approximately equal impedance with the help of built-in resistors, and can be replaced in this serial circuit. 
     Please refer to FIG. 3, which is a cross section of an LED display element with built-in resistors according to the invention. It is mainly composed of the LEDs  11 , pins  12 , the first resin  13 , the second resin  14 , and internal resistors  15 . The first resin  13  is transparent or can be painted with dye of the same color as that of the LEDs  11 . In bright environment, the LEDs  11  have similar visual effect even if they are off . The second resin can fix the pins  12  and internal resistors  15 . The size of the internal resistor  15  is determined by the number of serial LED display elements  10  on the circuit, power supply voltage, and the forward biases of various LEDs  11 . FIG. 4 shows another type of LED display element, the socket  16  takes the fashion of matching. The built-in resistors  17  are serially connected within and packaged with the transparent resin  18 , in the same manner as in FIG.  3 . 
     Please refer to FIG. 5A, which is an actual circuit of a display composed of multiple matrix modules driven by alternative currents according to the invention. The AC power supply has voltage VAC 1  and each of the modules M 1 , M 2 , . . . Mx is consisted by two series of equal number of LED display elements  10  with opposite polarities. All LED display elements  10  are adjusted via the corresponding built-in resistors to obtain roughly equal impedance. Driven by a specific current (about 20 mA), the total potential difference of all modules equals or roughly equals VAC 1 . When VAC 1  is positive, only the series of display elements with positive polarity in the module is lit up; while when VAC 1  reverses, only the other series is lit up instead. If the frequency of VAC 1  is shorter than the period of human temporary visual image retention, human eyes will not notice the alternative flashes of the LEDs. 
     Please refer to FIG.  5 B. We can also connect modules M 1 , M 2 , . . . Mx, with each LED display element in each module adjusted by the built-in resistor to make roughly equal impedance. The total potential difference of all modules driven by a specific current equals or roughly equals the DC power supply voltage. When the current flows through each module, we can produce various texts or graphics by the way the modules or the LED display elements are arranged. Therefore, different texts and graphics can be flexibly displayed with either a DC or an AC power supply. 
     Please refer to FIG.  6 . The spring chip switch  19  under the hole of the display board module is used as a switching device. When no LED display element  10  is plugged into the hole, the current will flow through this resistor and forms a closed loop; whereas if an LED display element  10  is inserted, the spring chip switch  19  will be disconnected from the circuit and get into contact with the positive and negative poles, allowing the current flow through the LED display element  10  but not the resistor R. A display with a larger area can be constructed by connecting multiple modules in parallel in such a method. FIG. 7 is an illustrative finctional plot of the invention with four 7×8 matrix modules. 
     Please refer to FIG. 8, which is an actual circuit of a display composed of multiple linear modules driven by direct currents according to the invention. The AC power supply has voltage VAC 2 , the power cords are W 1  and W 2 . The linear modules L 1 , L 2 , . . . Lx are composed by connecting L 11 , L 12 , L 21 , L 22 , . . . Lx 1 , and Lx 2  in series, respectively. The beginning of L 1 , L 2  and the end of Lx are connected to W 1 , while the connecting points between L 11  and L 12 , L 21  and L 22 , . . . Lx 1  and Lx 2  are connected to W 2 ; wherein each of L 11 , L 12 , L 21 , L 22 , . . . Lx 1 , Lx 2  consists of n LED display elements  10  connecting in series. The total potential difference of each series driven under a specific current (about 20 mA) equals or roughly equals VAC 2 . When W 1  is positive, only L 12 , L 22 , . . . Lx 2  are lit up. The LED display elements  10  in this linear module can be fixed to positions as needed, which is economical and convenient. 
     Many changes and modifications in the above described embodiment of the invention can, of course, be carried out without departing from the scope thereof. Accordingly, to promote the progress in science and the useful arts, the invention is disclosed and is intended to be limited only by the scope of the appended claims.