Variable resistance measuring loop having compensational function for environmental factors

Abstract

A variable resistance measuring loop having compensation function for environmental factor is disclosed. The measuring loop comprises a central processing unit CPU connected by one end of the variable resistance to the PO.1 leg thereof, and the other end being connected to the PO.2 leg thereof, the center end thereof being connected to a drain of a charging switch transistor Q, the base of the transistor Q being connected in series with a resistance R to the PO.3 leg of the CPU, the emitter of the transistor Q being connected to VDD power source end, the drain being conductive with the PO.0 leg and being connected in series with a charging/discharging capacitor C to a common ground, characterized in that the two ends of the variable resistance is connected to a control loop which is connected to a capacitor charging/discharging and the amount of movement is calculated via a discharging formula, and due to the two ends of the variable resistance is connected, the measuring loop is not affected by environment factors in the mouse cursor controller circuit.

Description

BACKGROUND OF THE INVENTION

[0001] (a) Field of the Invention

[0002] The present invention relates to a variable resistance measuring loop having compensation function for environmental factors, and in particular, a measuring loop used in a mouse cursor controller which will not be affected by environmental factors but will reduce defect rate of circuit and upgrade the precision of the mouse cursor controller.

[0003] (b) Description of the Prior Art

[0004] Among computer peripherals, a computer mouse cursor controller is indispensable in operating a computer, for instance, computer mouse, keyboard, handwritten board, joystick are peripherals which provide function for controlling the movement of the mouse cursor in controlling and operating the computer in documentation and image handling or games software.

[0005] Conventionally, the mouse cursor controller hardware is used to control the x-axis and y-axis movement on a display. In this controller, a RC charging/discharging circuit calculates the coordinate of movement based on the charging/discharging of the capacitor C. However, due to the influence of the environment, for instance, the changes of temperature and humidity, the value of the capacitor C of the RC charging/discharging circuit will be easily changed, and this will cause an unstable circuit and the controlling of mouse or joystick is not smooth. In a more serious case, the equipment may be damaged, and once damage is occurred, its calibration cannot be restored to its normal status.

[0006] Accordingly, it is an object of the present invention to provide a variable resistance measuring loop having compensational function for environment factors, wherein the loop is used in the mouse cursor controller circuit to overcome the above drawbacks.

SUMMARY OF THE INVENTION

[0007] Accordingly, it is an object of the present invention to provide a variable resistance measuring loop having compensation function for environmental factors, wherein the two ends of the variable resistance connected to a control loop which is connected to a capacitor charging/discharging are employed and the amount of movement is calculated via a discharging equation, and due to the two ends of the variable resistance is connected, the measuring loop is not affected by environment factors in the mouse cursor controller circuit.

[0008] Yet another object of the present invention to provide a variable resistance measuring loop having compensation function for environmental factors, wherein a central processing unit CPU is connected by one end of the variable resistance to the PO.1 leg, thereof and the other end is connected to the PO.2 leg thereof, the center end thereof is connected to a drain of a charging switch transistor Q, the base of the transistor Q is connected in series with a resistance R to the PO.3 leg of the CPU, the emitter of the transistor Q is connected to VDD power source end, the drain being conductive with the PO.0 leg and being connected in series with a charging/discharging capacitor C to a common ground, by means of the two ends of the variable resistance is connected to a control loop which is connected to a capacitor charging/discharging and the amount of movement is calculated via a discharging formula, and due to the two ends of the variable resistance is connected, the measuring loop is not affected by environment factors in the mouse cursor controller circuit.

BRIEF DESCRIPTION OF THE DRAWINGS

[0009] FIG. 1 is a circuit diagram of the present invention.

[0010] FIG. 2 is a charging/discharging waveform diagram of the present invention.

DETAILED DESCRIPTION OF THE PRESENT INVENTION

[0011] Referring to FIG. 1, there is shown a variable resistance measuring loop having compensation function for environmental factors comprising a central processing unit CPU, a discharging resistance VR, a charging capacitor C, a transistor used as charging switch, a base resistor R for current controlling.

[0012] In accordance with the present invention, the above CPU is INTEL 80c51 compatible, for instance, WINBOND w78c51, wherein the electrical properties are similar to INTEL 80c51. One end of the variable resistance is connected to PO.1 leg, the other end is connected to the PO.2 leg thereof, the center end thereof is connected to a drain of a charging switch transistor Q, the base of the transistor Q is connected in series with a resistance R to the PO.3 leg of the CPU, the emitter of the transistor Q is connected to VDD power source end, the drain is conductive with the PO.0 leg and is connected in series with a charging/discharging capacitor C to a common ground.

[0013] In accordance with the present invention, the working principle is as follows:

[0014] (1) Charging the loop:

[0015] the PO.0, PO.1, PO.2 of the CPU is set at input mode, and the PO.3 is set at output mode and the output is LOW. At this instance, current from VDD flows via the transistor Q to the capacitor to charge, as the transistor Q is triggered, to saturation, the saturated voltage equals to power source voltage VDD minus the saturated voltage VCE of the transistor,

[0016] (2) Discharging the loop:

[0017] the PO.0, PO.2, PO.3 leg of the CPU is set at input mode, and PO.1 is set at output mode, and the output is at LOW. At this instance, the transistor Q is cut off, and the capacitor C charging current flows through RA to PO.1. PO.1 detects the variation of discharging voltage, and the discharging is completed after a period of time. The discharging waveforms are shown in FIG. 2

[0018] (2.2) Discharging loop (2):

[0019] the PO.0, PO.1 and PO.3 leg of the CPU is set at input mode, and PO.2 is set at output mode, and the output is low. At this instance, the transistor is cut off, and the capacitor C charging current flows through RB to PO.2. PO.0 detects the variation of discharging voltage, and charging is completed after a period of time. The discharging waveforms are shown in FIG. 2.

[0020] As shown in the figure, the discharging equation is as follows:

[0021] (1) Discharging Equation

[0022] (2) 1$\begin{array}{cc}\mathrm{Discharging}\mathrm{Equation}Voltageforcapacitor{V}_C=V_{DD}·e^{-\frac{t}{RC}}\Rightarrow e^{-\frac{t}{RC}}=\frac{V_C}{V_{DD}}\Rightarrow l_n{e}^{-\frac{t}{RC}}=l_n\frac{V_C}{V_{DD}}\Rightarrow -\frac{t}{RC}=l_n\frac{V_C}{V_{DD}}\Rightarrow t=-RC{l}_n\frac{V_C}{V_{DD}}\Rightarrow t=RC{l}_n\frac{V_{DD}}{V_C}\Rightarrow t=RC{l}_n{V}_{DD}-\frac{V_{\mathrm{ce}\left(\mathrm{sat}\right)}}{VIL}& \left(1\right)\\ t_A=\frac{t_1}{t_1+t_2}=\frac{R_A·C{l}_n{V}_{DD}-\frac{V_{\mathrm{CE}\left(\mathrm{sat}\right)}}{VIL}}{R_A·C{l}_n{V}_{DD}-\frac{V_{\mathrm{CE}\left(\mathrm{sat}\right)}}{VIL}+R_B·C{l}_n{V}_{DD}-\frac{V_{\mathrm{CE}\left(\mathrm{sat}\right)}}{VIL}}=\frac{R_A}{R_A+R_B}& \left(2\right)\\ t_B=\frac{t_2}{t_1+t_2}=\frac{R_B·C{l}_n{V}_{DD}-\frac{V_{\mathrm{CE}\left(\mathrm{sat}\right)}}{VIL}}{R_A·C{l}_n{V}_{DD}-\frac{V_{\mathrm{CE}\left(\mathrm{SAT}\right)}}{VIL}+R_B·C{l}_n{V}_{DD}-\frac{V_{\mathrm{CE}\left(\mathrm{SAT}\right)}}{VIL}}=\frac{R_B}{R_A+R_B}& \left(3\right)\end{array}$

[0023] applying 2$\begin{array}{cc}Joystick=\frac{R_A}{R_A+R_B}\times \mathrm{Max}.output=JoystickReport& \left(1\right)\\ Mouse=\frac{R_A}{R_A+R_B}\times 255\to 0~255\Rightarrow Mousemoveme\mathrm{nt}-128~+127& \left(2\right)\end{array}$ RA+RB=VR

R A :0˜VR

R B :0˜VR

[0024] In view of the above, the present invention employs the two ends of the variable resistance being connected to a control loop which is connected to a capacitor charging/discharging and the amount of movement is calculated via a discharging formula, and due to the two ends of the variable resistance is connected, the measuring loop is not affected by environment factors in the application in the rrouse cursor controller circuit.

[0025] While the invention has been described with respect to preferred embodiment, it will be clear to those skilled in the art that modifications and improvements may be made to the invention without departing from the spirit and scope of the invention. Therefore, the invention is not to be limited by the specific illustrative embodiment, but only by the scope of the appended claims.

Claims

1. A variable resistance measuring loop having compensational function for environment factors comprising a central processing unit CPU connected by one end of the variable resistance to the PO.1 leg thereof, and the other end being connected to the PO.2 leg thereof, the center end thereof being connected to a drain of a charging switch transistor Q, the base of the transistor Q being connected in series with a resistance R to the PO.3 leg of the CPU, the emitter of the transistor Q being connected to VDD power source end, the drain being conductive with the PO.0 leg and being connected in series with a charging/discharging capacitor C to a common ground, wherein the charging loop is that the PO.0, PO.1, PO.2 of the CPU are set at input mode, the PO.3 is set at output mode and the output is LOW, at this instance, current from VDD flows via the transistor Q to the capacitor to charge, as the transistor Q is triggered, to saturation, the saturated voltage equals to power source voltage VDD minus the saturated voltage VCE of the transistor, and the discharging loop is: the discharging loop (1): the PO.0, PO.2, PO.3 leg of the CPU are set at input mode, and PO.1 is set at output mode, and the output is at LOW, at this instance, the transistor Q is cut off, and the capacitor C charging current flows through RA to PO.1, the PO.1 detects the variation of discharging voltage, and the discharging step is completed after a period of time; the discharging loop (2): the PO.0, PO.1 and PO.3 leg of the CPU are set at input mode, PO.2 is set at output mode, and the output is low, at this instance, the transistor Q is cut off, and the capacitor C charging current flows through RB to PO.2, the PO.0 detects the variation of the discharging voltage, and the discharging is completed after a period of time; characterized in that the two ends of the variable resistance is connected to a control loop which is connected to a capacitor charging/discharging and the amount of movement is calculated via a discharging formula, and due to the two ends of the variable resistance is connected, the measuring loop is not affected by environment factors in the application in the mouse cursor controller circuit.

2. The variable resistance measuring loop of claim 1, wherein the discharging equation is: