Abstract:
This invention refers to peripheral equipment of a computer and is a wireless and passive tablet for inputting to the computer that converts the track of handwriting to digital X, Y coordinates and then inputs it to the computer and then displays the track on screen of the computer. The characteristic of the wireless and passive tablet is using the coil of X, Y direction in transmitting and receiving. A square wave is generated and input to a transmitting circuit. A transmitted electromagnetic wave is inputted to a circuit of a pen to form resonance that will be outputted to a receiving circuit. The receiving circuit connects to an amplifying circuit to amplify the signal and input the amplified signal into a phase angle detecting circuit and an amplitude detecting circuit respectively to control the phase angle and amplitude. And then the signal is inputted to a primary CPU to realize the writing function of the wireless pen.

Description:
FIELD OF THE INVENTION 
   This invention relates to a peripheral equipment of a computer. A main function of the apparatus according to the present invention is to convert tracks of handwriting to digital values, that is, X and Y coordinates and then input them into a computer. With the help of corresponding driver programs and applications, it can display tracks that a user draws on the tablet directly on the screen of computer. The tablet is primarily applied in the fields of handwriting identification system and drawing. 
   DESCRIPTION OF THE PRIOR ART 
   By far, there are several tablet hardware manufacturers such as the WACOM in Japan, the AIPTEK in Taiwan and the HanWang Technology Co., Ltd. in China. After several years of development, the tablet technique has been on the way to be matured. And more tablet products have come into the world and are on hot sale, such as wired tablet, wireless tablet, wired pressure-sensitive tablet, wireless pressure-sensitive tablet and the like. By principle, all these tablets may be divided into such kinds as the electromagnetic one, the touchable one, the ultrasonic-localizing one, the photoelectric one and so on. Till now, the WACOM Company in Japan is the major in manufacturing wireless and passive tablets in the industrial circles. The patents of WACOM&#39;s tablet have following two features: one is that the transmitting coil and the receiving coil are just the same one; the other is that it first emits an electromagnetic wave with the same frequency as a resonance frequency of a pen circuit for a period of time so as to resonate the inductor and capacitors in the pen circuit, then it stops emitting and switches to a receiving state, and thereafter the oscillation of resonant wave in the pen circuit will be attenuated, for there is no outer impetus to the inductors and capacitors in the pen circuit. The procedure above described is illustrated in  FIG. 3 . Now a signal is extracted out through an amplifying and filtering circuit to finally determine the coordinate values of X and Y. 
   SUMMARY OF THE INVENTION 
   The present invention is such a wireless and passive pressure-sensitive tableting apparatus. Wherein the term “wireless” means that nothing wires a pen and a tablet. And the term “passive” means that no battery is in the pen. And the term “pressure-sensitive” means that the tablet could sense the pen&#39;s pressure. The principal points of technique adopted in the present invention to determine the coordinate values of X and Y and to sense the pen&#39;s pressure are illustrated in  FIG. 1 : wherein auxiliary CPU (MCU2) generates a square wave and inputs it to a transmitting circuit, the transmitted electromagnetic wave is inputted to a pen circuit to form resonance, then output to a receiving circuit and amplified by an amplifying circuit, which is connected with an output of the receiving circuit, then the resultant signal is input to a phase angle and an amplitude detecting circuit to conduct phase angle detection and amplitude detection. After an integrating circuit, a signal is input to primary CPU. Thus, the function of inputting to the computer with a wireless passive pen has been realized. The operating process is as follows: a square wave, generated by the auxiliary CPU (MCU2), is inputted to a transmitting circuit. An electromagnetic wave, whose waveform is shown in  FIG. 2 , is transmitted continuously through the coils of Y direction. By Fourier Transform, it is known that the square wave has higher harmonics with the frequencies of odd times of its own. And the resonance frequency determined by the inductors and capacitors of the pen is just a certain odd times of the square wave&#39;s frequency. Therefore, once the pen&#39;s resonant coil is induced by the higher harmonics of the square wave of the tablet&#39;s coil, it will resonate; and once a resonance signal is received by the coil of X direction of the receiving circuit, it will be amplified by the amplifying circuit and then input to the phase angle and amplitude detecting circuit, where the signal&#39;s are divided into I phase and J phase. Finally, inputting the signals with I phase and signals with J phase into the CPU via the integrating circuit. The primary CPU calculates the amplitude and phase angle, wherein the amplitude corresponding to the coordinate values of X and Y, and the phase angle being direct proportion to the pen&#39;s pressure. When the pen tip is pressed down, the pen&#39;s resonance phase deviates because of variation of the inductance in the pen. Therefore, current pressure from the pen can be obtained by measuring the very phase angle. 
   Differing from the tablet of WACOM Company, the present invention accomplishes its signal transmitting and receiving through the coils of direction Y and X respectively. Besides this, transmitting and receiving procedures of the present invention are conducted continuously, but not in an alternative way as the tablet of WACOM Company do. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a system block diagram of a wireless and passive tableting apparatus for inputting to computer; 
       FIG. 2  shows waveforms transmitted electromagnetic wave according to the present invention; 
       FIG. 3  shows waveforms of the resonance&#39;s decaying oscillation of the WACOM tablet; 
       FIG. 4  is a transmitting circuit and receiving circuit according to the present invention; 
       FIG. 5  is an amplifying circuit according to the present invention; 
       FIG. 6  is a phase angle and amplitude detecting circuit according to the present invention; 
       FIG. 7  is an integrating circuit according to the present invention. 
       FIG. 8  is a pen&#39;s paralleled resonant circuit of the present invention; 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Hereinafter, the invention will be described in conjunction with the preferred embodiments and drawings. 
     FIG. 1  shows a block diagram of the system according to the present invention. An auxiliary CPU, which generates a square wave, connects with a transmitting circuit, which can transmit electromagnetic wave continuously. A pen circuit receives the electromagnetic wave transmitted from the transmitting circuit to produce a resonant signal. Then the resonant signal is transmitted to receiving circuit continuously, and amplified by an amplifying circuit that connects with the receiving circuit. The amplified signals is inputted into an phase angle and amplitude detecting circuit, and the signals output from the phase angle and amplitude detecting circuit are inputted into a primary CPU via and integrating circuit. 
   A waveform of a transmitted electromagnetic wave according to the present invention is shown in  FIG. 2 , wherein its cycle is of odd times of a resonance cycle determined by the inductors and capacitors in the pen. 
   The transmitting circuit and receiving circuit of the present invention are illustrated in  FIG. 4 , wherein the part in the direction of Y is a continuous transmitting circuit. By sequentially gating the transmitting circuits Y 1 , Y 2  . . . Y 18  . . . Y 24 , and regularly gating the receiving circuits X 1 , X 2  . . . X 18  . . . X 24  in turn, the position in Y coils can be determined for the pen according to the strength of a received signal, that is, which Y coils the pen locates can be determined. Similarly, by regularly gating the transmitting circuits Y 1 , Y 2  . . . Y 18  . . . Y 24  in turn, and sequentially gating the receiving circuits X 1 , X 2  . . . X 18  . . . X 24 , which X coils the pen locates can be determined also. Following is the practical connection of the circuit: the transmitting circuits are in the direction of Y and the receiving circuits are in the direction of X. L 10 , L 11 , L 12 , L 13 , L 14  and L 15  stand for chips, among which L 13 , L 14  and L 15  are adopted for transmitting signals and L 10 , L 11  and L 12  are adopted for receiving signals. A square wave signal, generated by an auxiliary CPU (MCU2), is inputted into pin  3  (X port) of chips L 13 , L 14  and L 15  respectively via the RX+ terminals of the transmitting circuit shown in  FIG. 5 . For chip L 13 , its X 0 ˜X 7  ports corresponding to pins  13 ,  14 ,  15 ,  12 ,  1 ,  5 ,  2  and  4  connect with the the coils in the direction of Y respectively, the output terminals of the coils are grounded; INH terminal corresponding to pin  6  is used for chip selection; A terminal, B terminal and C terminal corresponding to pins  11 ,  10  and  9  are gating terminals, all connecting with the primary CPU; VEE terminal corresponding to pin  7  is connected to a negative voltage. For chip L 14 , its X 0 ˜X 7  ports corresponding to pins  13 ,  14 ,  15 ,  12 ,  1 ,  5 ,  2  and  4  connect with the coils in the direction of Y respectively, the output terminals the coils are grounded; INH terminal corresponding to pin  6  is used for chip selection; A terminal, B terminal and C terminal corresponding to pins  11 ,  10  and  9  are gating terminals, all connecting with the primary CPU; VEE terminal corresponding to pin  7  is connected to a negative voltage. And for L 15 , its X 0 ˜X 7  ports corresponding to pins  13 ,  14 ,  15 ,  12 ,  1 ,  5 ,  2  and  4  connect with the coils in the direction of Y respectively, the output terminals of the coils are grounded; INH terminal corresponding to pin  6  is used for chip election; A terminal, B terminal and C terminal corresponding to pins  11 ,  10  and  9  are gating terminals, all connecting with the primary CPU; VEE terminal corresponding to pin  7  is connected to a negative voltage. The RX+ terminals of the receiving circuit connect with the pin  3  (X ports) of chip L 10 , chip L 11  and chip L 12  to output the received signal into the amplifying circuit. For chip L 10 , its X 0 ˜X 7  ports corresponding to pins  13 ,  14 ,  15 ,  12 ,  1 ,  5 ,  2  and  4  connect with the coils in the direction of X respectively, the output terminals of the coils are grounded; INH terminal corresponding to pin  6  is used for chip selection; A terminal, B terminal and C terminal corresponding to pins  11 ,  10  and  9  are gating terminals, all connecting with the primary CPU; VEE terminal corresponding to pin  7  is connected to a negative voltage. For chip L 11 , its X 0 ˜X 7  ports corresponding to pins  13 ,  14 ,  15 ,  1 ,  5 ,  2  and  4  connect with the coils in the direction of X respectively, the output terminals of the coils are grounded; INH terminal corresponding to pin  6  is used for chip selection; A terminal, B terminal and C terminal corresponding to pins  11 ,  10  and  9  are gating terminals, all connecting with the primary CPU; VEE terminal corresponding to pin  7  is connected to a negative voltage. And for L 12 , its X 0 ˜X 7  ports corresponding to pins  13 ,  14 ,  15 ,  1 ,  5 ,  2  and  4  connect with the coils in the direction of X respectively, the output terminals of the coils are grounded; INH terminal corresponding to pin  6  is used for chip election; A terminal, B terminal and C terminal corresponding to pins  11 ,  10  and  9  are gating terminals, all connecting with the primary CPU; VEE terminal corresponding to pin  7  is connected to a negative voltage. 
   An amplifying circuit according to the present invention is shown in  FIG. 5  wherein an AGC (automatic gain control) circuit, controlled by the primary CPU, is used to eliminate the signal&#39;s distortion resulted from the variation of the distance between the pen and the tablet. The received signal is coupled into the circuit via RX+ terminal, which connects with ends of two parallel resistors R 1  and R 2 . The other end of the resistor R 2  connects with pin  2  of an amplifier IC 12 A and one end of a resistor R 3  in parallel, and the other end of the resistor R 3  connects with pin  1  of IC 12 A, pin  12  of chip IC 14  and one end of resistor  6 . The pin  4  of the IC 12 A is connected to analogue ground. The other end of resistor R 1  connects with one end of a resistor R 4 , a capacitor C 6  and a reference voltage terminal (Vref) in parallel. The other end of the resistor R 4  connects with pin  3  of the chip IC 12 A. The other end of the capacitor C 6  is connected to analogue ground and one end of a capacitor C 7 . The other end of the capacitor C 7  connects with the pin  8  of the chip IC 12 A and power supply VDD. The other end of the resistor R 6  connects with pin  13  of chip IC 14  and one end of a resistor R 7 . The other end of the resistor R 7  connects with the pin  14  of chip IC 14  and one end of a resistor R 8 . The other end of the resistor R 8  connects with pin  15  of chip IC 14  and one end of the resistor R 9 . The other end of the resistor R 9  connects with pin  1  of chip IC 14  and one end of a resistor R 10 . The other end of the resistor R 10  connects with pin  2  of chip IC 14  and one end of a resistor R 11 . The other end of the resistor R 11  connects with pin  4  of chip IC 14  and one end of a resistor R 12 . The other end of the resistor R 12  connects with pin  5  of chip IC 14  and one end of a resistor R 13 . The other end of the resistor R 13  connects with a reference voltage terminal (Vref). The pin  3  of chip IC 14  connects with one end of a capacitor C 1 , the other end of the capacitor C 1  connects with one end of resistor R 16  and the pin  5  of chip IC 12 B. The other end of the resistor R 16  connects with the reference voltage terminal (Vref). The pin  7  of chip IC 12 B, which outputs the output signals, connects with one end of the resistor R 26 . The other end of the resistor R 26  connects with pin  6  of chip IC 12 B and one end of a resistor R 23 . The other end of the resistor R 23  connects with the reference voltage terminal (Vref). Pin  11  of chip IC 14  connects with a signal GA, and pin  10  of chip IC 14  connects with a signal GB and pin  9  of chip IC 14  connects with a signal GC, and pin  16  of chip IC 14  connects with a power supply VDD and one end of a capacitor C 14 . The other end of the capacitor C 14  connects with the analogue ground, and so do pin  6 , pin  7  and pin  8  of chip IC 14 . 
   The phase angle and amplitude detecting circuit of the present invention is shown in  FIG. 6 . It is designed to shape the transmitted square wave by eliminating the spikes on the rising edges and on the falling edges. With various of combination of turning ON/OFF of switches IC 8 B and IC 8 C, the inputted signals are changed into two set of signals having a phase angle difference of 90 degree, which are defined as I phase and J phase respectively. Specifically, an amplified signal is coupled into the circuit via the IN terminal, which connects with pin  3  of a chip IC 9 A and one end of a resistor R 17  in parallel. The other end of the resistor R 17  connects with pin  6  of chip IC 9 B and one end of a resistor R 18  in parallel. The other end of the resistor R 18  connects with pin  7  of chip IC 9 B and pin  4  of chip IC 8 B in parallel. Pin  5  of chip IC 9 B connects with one end of a resistor R 19 . The other end of the resistor R 19  connects with a reference voltage. Pin  1  of chip IC 9 A connects with pin  2  of chip IC 9 A and pin  8  of chip IC 8 C. Pin  8  of chip IC 9 A is connected to a power supply VDD, and pin  4  of chip IC 9 A connects with an analogue ground. Pin  5  of chip IC 8 B connects with pin  2  of MCU2. Pin  6  of chip IC 8 C connects with pin  3  of MCU2. Pin  3  of chip IC 8 B and pin  9  of chip IC 8 C are connected together, used as the output terminal to output the detected phase angle and amplitude signals. Pin  11  of MCU2 connects with ends of a capacitor C 4  and a resistor R 28  respectively, wherein the two other ends of the capacitor C 4  and the resistor R 28  are connected together to connect with a base of a triode Q 1 , whose emitter connects with one end of a capacitor C 3  in series. The other end of the capacitor C 3  connects with one end of a resistor R 29  and TX− terminal in parallel. The other end of the resistor R 29  connects with power supply VEE. A collector of the triode Q 1  connects with TX+ terminal and one end of a capacitor C 2  in parallel. And the other end of the capacitor C 2  connects with TX− terminal. Pin  5  of MCU2 connects with an OSC clock, and pin  1  of MCU2 connects with ends of a resistor R 25  and a capacitor C 5  in parallel. The other end of the resistor R 25  connects with a power supply VCC, and the other end of the capacitor C 5  is grounded. Hang up such pins of MCU2 as pin  4 , pin  6 , pin  7 , pin  8 , pin  9 , pin  12 , pin  13  and pin  14 . But let its pin  15  connect with DONE, its pin  16  connect with CMDO, its pin  17  connect with CMD 1 , its pin  18  connect with CMD 2 , its pin  19  connect with CMD 3 , and its pin  20  connect with VCC and one end of a capacitor C 19  in parallel. The other end of the capacitor C 19  connects with pin  10  of MCU2 and the ground in parallel. 
   The integrating circuit of the present invention is shown in  FIG. 7 . The IN terminal of the integrating circuit is connected to the OUT terminal. There are two sets of signals having a phase difference of 90 degree, that is, I phase and J phase. Signals with I phase and J phase are inputted into primary CPU via the integrating circuit, and the primary CPU calculates the phase angle and amplitude, wherein the corresponds to the pen&#39;s pressure. After shaped by the phase angle and amplitude detecting circuit. a signal is coupled into the integrating circuit via the IN terminal, which connects with one end of a resistor R 21  in series. The other end of the resistor R 21  connects with pin  2  of chip IC 10 A, pin  11  of IC 8 D and one end of a capacitor C 21  in parallel. The other end of the capacitor C 21  connects with pin  10  of chip IC 8 D and pin  1  of chip IC 10 A in parallel. Pin  12  of chip IC 8 D connects with the primary CPU. And for chip IC 10 A, its pin  3  connects with the reference voltage, pin  4  connects with the analogue ground, pin  8  connects with the power supply VDD, and pin  1  connects with one end of a resistor R 20 . The other end of the resistor R 20  is used as the output terminal and connected with the primary CPU. 
   The pen circuit primarily comprises a paralleled resonant circuit composed of capacitors and inductors. And the connection relations are illustrated in  FIG. 8 , wherein an inductor L 1  connects with a variable capacitor C 1  and the capacitors C 2 , C 3 , C 4 , C 5 , C 6  and C 7  in parallel. Then the last two ends of the circuit connect with a switch K 1  and a resistor R 1  in series respectively, to form a loop. Herein, K 1  is a switch on the side of the pen, functioning as the right button of a mouse. 
   A kind of wireless, passive and pressure-sensitive tableting apparatus is described in the present invention. The resonant circuit in the pen is composed of inductors and capacitors connected in parallel. And the tablet comprises a transmitting circuit, a receiving circuit, an amplifying circuit, a phase angle and amplitude detecting circuit and an integrating circuit. During the process of operation, the user takes hold of the pen to write and draw freely on the tablet with suitable pressure (the switch on the side of the pen acts as the right button of a mouse). With the help of the pen, hardware in the tablet and the corresponding application, the handwriting track that the user made on the tablet just now could be displayed on the computer screen. Thus, the object of inputting handwriting into a computer with the wireless and passive method is well achieved. For instance, once a Chinese word “           ” is written on the tablet with the equipped pen, it will be displayed on the computer screen immediately. Thus, the present invention makes it more convenient in computer inputting of Chinese words.