CN103970356B - Handwriting drawing board and displaying method of handwriting drawing board - Google Patents
Handwriting drawing board and displaying method of handwriting drawing board Download PDFInfo
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- CN103970356B CN103970356B CN201410186989.XA CN201410186989A CN103970356B CN 103970356 B CN103970356 B CN 103970356B CN 201410186989 A CN201410186989 A CN 201410186989A CN 103970356 B CN103970356 B CN 103970356B
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Abstract
The invention discloses a handwriting drawing board which comprises a handwriting board body, a meter pen, a control module, a power module, an MOS tube module, a voltage collecting and amplification module and a displaying module, wherein an analog-digital converter is arranged in the control module. The voltage drop is generated at the position of a contact point of the meter pen in the mode that constant-current pulses are controlled by the control module to alternatively pass through the two diagonal lines of the handwriting board body, low-noise amplification and high-speed collecting are carried out, finally data processing is carried out through the control module, and a coordinate value is obtained through calculation and output to be displayed. According to the handwriting drawing board, coordinates of the contact point can be accurately displayed, and the error is smaller than 5 mm. Algorithms like data fitting are adopted for the control module, and then the functions of contact point movement tracking, graphing, character writing and the like can be achieved. The maximum resolution of the handwriting drawing board ranges from 1 mm to 3 mm, and meanwhile low-power-dissipation design is achieved.
Description
Technical field
The present invention relates to a kind of hand-written drawing board and its display methods.
Background technology
For hand-written drawing board, most important index includes: the degree of accuracy of positioning, reaction speed, display precision and power consumption
Control and the ability of graphic plotting.Existing positioning mode has several as follows:
1st, double bridge measuring resistance is adopted to position.By double bridge respectively between measurement table style of writing point and four angles etc.
Effect resistance, then calculate contact position, but handwriting pad resistance is too little, and gauge outfit resistance and conductor resistance can be more than copper-clad plate resistance
Greatly, its value is also unstable, causes measure error big, and bridge measurement speed is slow, realizes difficulty big.
2nd, with vibration Measuring Frequency Method, due to copper-clad plate resistance minimum it may be considered that in larger capacitance form oscillating circuit, measurement
Its frequency.According to contact position measure of the change frequency change, thus calculating its resistance value, then determine corresponding coordinate position.Lack
Point: larger capacitance precision is low, when frequency of oscillation is higher, measure error also greatly it is considered to copper-clad plate distribution of resistance is uneven, is counted again
Calculate its coordinate value, increased deviation accumulation, effect is bad.
3rd, replace voltage at xy axle (horizontal vertical) supplying measure contact, this is the method for conventional, electric-resistance touch-screen.First will
Two angles of horizontal direction are connected two-by-two, and same burning voltage, voltage at metering contact, determine its x coordinate, then by upright position two
Angle is connected, and the measurement that is energized, and obtains y-coordinate.Because copper-clad plate resistance is little, the electric current passing through is big, and power dissipation ratio is larger, test pencil resistance
And conductor resistance causes measure error big.This suitable high resistant handwriting pad, needs to merge corner horizontal vertical twice.Due to four
Angle Position is located at copper-clad plate edge, and intermediate electric potential distribution is very uneven, and error is larger.
For the defect of prior art, need existing hand-written drawing board is made improvements, propose a kind of accurate positioning, anti-
Should fast, the high hand-written drawing board with ability low in energy consumption and that there is stronger graphic plotting of display precision.
Content of the invention
It is an object of the invention to overcoming the deficiencies in the prior art, provide a kind of hand-written drawing board, it is possible to achieve positioning is accurate
Really, react fast, display precision high with ability low in energy consumption and that there is stronger graphic plotting.
In order to achieve the above object, the present invention employs the following technical solutions: includes power module, handwriting pad, test pencil, mos
Tube module, voltage acquisition and amplification module, control module and display module；
Described power module is electrically connected with described control module, constant current source module and voltage amplification module；
Described handwriting pad is copper-clad plate；
Described mos tube module includes four mos pipes and the drive circuit with input and output end；This four mos pipes
Source electrode respectively correspondingly electrically connect with four angles of this handwriting pad, the drain electrode of two on diagonal mos pipe connects power supply respectively
With ground；Wherein on handwriting pad, the position of the grounded drain of mos pipe is low potential point；The input of described drive circuit and control mould
The control port electrical connection of block, output end is electrically connected with the grid of mos pipe；
Described voltage acquisition and amplification module include electronic switching circuit and amplifying circuit；Described electronic switching circuit has
Two select end, a control signal input and an output end；Described two selection ends are electric with two low potential points respectively
Connect；Described control signal input port is electrically connected with control module；Described output end is electrically connected with the input of amplification module；
Described amplification module is differential amplifier circuit, has a normal phase input end, an inverting input and an output end；Described
Normal phase input end is electrically connected with test pencil, and described inverting input is electrically connected with the output end of electronic switching circuit；Described output end
Electrically connect with control module；
Described control module includes analog-digital converter and holder；This holder has the number of magnitude of voltage and actual coordinate value
Learn corresponding relation, it is obtained by experimental data in advance；
Described display module receives the signal of control module, the contact position with test pencil on display handwriting pad；
When test pencil touches handwriting pad, described control module is switched fast two groups pairs of handwriting pad by mos tube module
Linea angulata turns on, and switches electronic switching circuit with identical switching rate simultaneously, makes the output end of electronic switching circuit always on
The low potential point of handwriting pad；Described voltage acquisition gathers the voltage difference of test pencil and low potential with amplification module and amplifies；Described mould
This voltage conversion is obtained two digital voltage values by number converter；Described control module call magnitude of voltage stored by holder with
The mathematics corresponding relation of actual coordinate value, magnitude of voltage is converted to actual coordinate, and sends and show to display module.At this
In the hand-written drawing board of invention, constant-current source connects copper-clad plate corner, and alternately switching break-make produces burning voltage.Amplifying circuit is by table
After magnitude of voltage amplification at pen and copper-clad plate contact point, at built-in high speed through control module, the analog-digital converter collection of high accuracy a
Reason, finally by Data Analysis Services, sets up Potential Distributing Mathematical Modeling and determines its coordinate value, improves essence through coordinate value correction chart
Show on display module after degree.Equipment total power consumption in 12v direct current supply is about 1.18w, mainly employs pulse width and adjusts
Make (pwm) to control the quick on-off of constant-current source to reach low power operation.This handwriting pad achieves contact motion by software
Tracking, Freehandhand-drawing circle and the function of simply writing.
Further, this control module also includes a timer, by this timer to described FET export pwm ripple Lai
Control the break-make of FET.Realized by pwm ripple: control the logical of corresponding FET, measurement using before adc collection with io mouth
Complete control with io mouth again closes the disconnected of FET.The time of so high level is used only for measure analog amount, when low level
Between judge carrying out data operation and various logic, the time that high current is turned on is significantly reduced to minimum, greatly reduces power consumption.
Further, described power module includes two groups of dc/dc conversions, and one of which dc/dc is changed by adjustable voltage stabilizing
Chip will be powered to mos tube module after power voltage step down；Another group of dc/dc changes after linear voltage stabilization successively respectively to control mould
Block is powered with amplification module with voltage acquisition.
Further, the display screen of described display module is divided into four quadrant areas, and it obtains the signal of control module, leads to
Cross the place quadrant of the current contact point of text importing.
It is a further object of the present invention to provide a kind of display methods of hand-written drawing board.A kind of display side of hand-written drawing board
Method, comprises the following steps:
Step one: by the mathematics corresponding relation of the holder stored voltage value of control module and actual coordinate value, its by
Experimental data obtains in advance；
Step 2: by the analog-digital converter of control module and display module initialization；
Step 3: determine the position contacting with handwriting pad by test pencil；
Step 4: the alternately switching cornerwise conducting of handwriting pad two, two electricity at this contact point are measured by test pencil
Pressure value；
Step 5: with amplification module, this two magnitudes of voltage are amplified by voltage acquisition；
Step 6: this two magnitudes of voltage are converted to by digital quantity v1 and v2 by the analog-digital converter of control module；
Step 7: call the magnitude of voltage of holder storage and the mathematics corresponding relation of actual coordinate value, obtain v1 and v2 institute
Corresponding actual coordinate value x and y；
Step 8: the value of x and y is sent and shows to display module, and be back to step 3.
Further, in step 2, the timer initialization of control module sets the frequency of pwm ripple；In step 4
In, control module sends pwm ripple to four FETs electrically connecting with the corner on this handwriting pad respectively, alternately switches same
The connection of cornerwise two FETs.
Further, between step 6 and step 7, also comprise the steps: v1 and v2 of repeated detection same position,
And calculate its mean value.Improve the precision of display further.
Further, between step 2 and step 3, the control instruction according to user selects to paint dot pattern or drawing mould
Formula；Between step 7 and step 8, judgment model is to paint dot pattern or Graphics Mode, if painting dot pattern, sentences further
Whether disconnected coordinate value changes, if changing, display module being initialized, if not changing, being directly entered step 8；If drawing
Pattern, then be directly entered step 8.Graphics Mode can be realized and paint dot pattern.
Further, in step 8, gone out currently by text importing according to the value of x and y in the display screen of display module
The quadrant that contact point is located.
Brief description
Fig. 1 is the structured flowchart of a kind of hand-written drawing board of the present invention
Fig. 2 is the connection figure with mos pipe for the handwriting pad of the present invention
Fig. 3 is contact position current potential view
Fig. 4 is to record alternate voltages view
Fig. 5 is contact actual measured value x coordinate surface chart
Fig. 6 is contact actual measured value y-coordinate surface chart
Fig. 7 is the display methods flow chart of a kind of hand-written drawing board of the present invention
Fig. 8 is the circuit diagram of the mos tube module of embodiment one
Fig. 9 is the circuit diagram with amplification module for the voltage acquisition of embodiment one
Figure 10 is the circuit diagram of the power module of embodiment one
Figure 11 is the circuit total figure of embodiment one
Figure 12 is the test schematic diagram of embodiment one
Figure 13 is the circuit diagram of the mos tube module of embodiment two
Figure 14 is the circuit diagram with amplification module for the voltage acquisition of embodiment two
Figure 15 is the circuit diagram of the power module of embodiment two
Referring to drawings and the specific embodiments, the invention will be further described.
Specific embodiment
Refer to Fig. 1, it is a kind of structured flowchart of handwriting pad of the present invention.A kind of hand-written drawing board of the present invention, bag
Include power module 1, handwriting pad 2, mos tube module 3, voltage acquisition and amplification module 4, control module 5 and display module 6.Should
Power module 1 is electrically connected with amplification module 4, control module 5 and display module 6 with this mos tube module 3, voltage acquisition respectively,
There is provided suitable operating voltage for this mos tube module 3, voltage acquisition and amplification module 4, control module 5 and display module 6.
This handwriting pad 2 is copper-clad plate.This mos tube module 3 includes four mos pipes and its respective driving with input and output end
Circuit.As shown in Fig. 2 being the connection figure with mos pipe for the handwriting pad of the present invention.Described four mos pipes respectively with this handwriting pad 2
Four angle electrical connections.This mos manages as three terminal device；Wherein, the output end of the first termination drive circuit, and this drive circuit is defeated
Enter end to electrically connect with the control port of this control module 5, drive this mos to manage by this drive circuit, reach and be switched fast this mos pipe
The purpose of break-make；One angle of the second termination handwriting pad 2；3rd termination power or ground connection, specifically, have the of two mos pipes
Three termination powers, the 3rd end ground connection of two other mos pipe, and two angles on a pair of linea angulata of handwriting pad 2 must be distinguished
There is a mos pipe connecing power supply and a ground connection, thus when two FETs on same diagonal are opened, power module
1 is passed through constant current to this diagonal of handwriting pad 2, and same diagonal has a high voltage and a low potential point.Described
The control port output pwm ripple of control module 5, is input to mos pipe through overdrive circuit, is switched fast mos pipe by pwm ripple
Break-make, makes handwriting pad 2 turn on from one group of diagonal, is switched to another group of cornerwise conducting.Described voltage acquisition and amplification mould
Block includes electronic switching circuit and amplifying circuit.Described electronic switching circuit is multi-terminal device, two termination low potentials therein
Point, the control port of input termination control module 5, output termination amplifying circuit, for switching low potential point, the speed of its switching
Should be consistent with the speed of diagonal switching.Two inputs of described amplifying circuit connect the output end of electronic switching circuit respectively
(voltage of low potential) and test pencil.This test pencil touches and can collect a magnitude of voltage during handwriting pad 2.The voltage of low potential and table
The collection voltages of pen, after the differential amplification of amplifying circuit, feed back to control module 5.When cornerwise two fields of one of which
During the conducting of effect pipe, described voltage acquisition gathers the voltage of test pencil and low potential with amplification module and is amplified, and obtains voltage
Value v1 simultaneously feeds back to control module 5；Control module 5 switches two FET conductings of the diagonal play of another set again, cuts simultaneously
Change low potential point, state voltage acquisition and gather the voltage of test pencil and low potential with amplification module and amplified, obtain magnitude of voltage v2
And feed back to control module 5.Correspond to the same coordinate (x, y) on handwriting pad, control module 5 can collect two electricity
Pressure value v1 and v2, as shown in figure 3, it is contact potential schematic diagram.This control module 5 will according to the Potential Equivalent Model pre-setting
(v1, v2) is converted into actual coordinate (x, y), is then forwarded to display module 6 and displays it.
Described control module 5 includes analog-digital converter, holder and timer.Described voltage is adopted by this analog-digital converter
The analog voltage that collection is amplified with amplification module 4 is converted to digital quantity.This holder has the number of magnitude of voltage and actual coordinate value
Learn corresponding relation, it is obtained by experimental data in advance.This timer is used for the timing of pwm ripple.
The principle of the copper-clad plate coordinate setting of the present invention is as follows:
A is used respectively in four angles of handwriting pad 2, and b, c and d represent.Test pencil contact handwriting pad 2 when, be respectively adopted 0.5a～
Constant current conducting copper-clad plate a, c or the b of 1a, d diagonal position.As shown in figure 3, it is contact position current potential view.As a and c
Or during b and d conducting, by high-speed sampling, measure the voltage at handwriting pad 2 upper contact, measurement twice respectively obtains two electricity
Pressure value v1 and v2, as shown in figure 4, it is to record alternate voltages view.Through multiple spot position measurement, obtain different positions in copper-clad plate
Two magnitudes of voltage put.Using mablab data matching, by these discrete coordinate points positional values and two diagonal turn-on voltages
Relation fit to surface equation it is possible to realize the coordinate setting of copper-clad plate.So, when contacting copper-clad plate diverse location,
According to above data fitting result, through control module 5 algorithm process it is possible to obtain coordinate position.(during wherein a and b conducting
Connecing reference power source positive pole, ground connection during c and d conducting) break-make of fet switch is by pwm control realization, thus realizing perseverance
Stream passes through handwriting pad 2.It is very easily that diagonal alternate conduction control control module 5 is realized.As shown in figure 4, it is to survey
Obtain alternate voltages view.
The data processing method of coordinate value positioning is as follows:
Obtain coordinate (x, y) and the data mapping tables of (v1, v2) through mass data after measuring, using matlab mathematics
Software carries out data matching, obtains both corresponding relations, and discrete point is fitted to continuous curve surface relation for relation.Pass through
Two-way ad collection voltage results, respectively as x coordinate and y-coordinate, contact actual measurement coordinate value horizontal stroke, ordinate respectively as
Z-axis, draws the relation of horizontal stroke, ordinate and (v1, v2) respectively.As shown in Figure 5 and Figure 6, wherein Fig. 5 is matching surface chart out
Contact actual measured value x coordinate surface chart, Fig. 6 is contact actual measured value y-coordinate surface chart.In actual measurement, between sampled data
Every less, sampled data is more, and the precision obtaining is higher.
Further, the present invention also provides the display methods of above-mentioned hand-written drawing board.As shown in fig. 7, it is the hand of the present invention
Write the display methods flow chart of drawing board, specifically include following steps:
S1: test in advance: obtain coordinate (x, y) and the data mapping tables of (v1, v2) through mass data after measuring, profit
Carry out data matching with matlab mathematical software, obtain both corresponding relations, and stored by the holder of control module 5
Come.
S2: the analog-digital converter of control module 5, timer and display module 6 are initialized, sets the frequency of pwm ripple
With dutycycle.
S3: the control instruction according to user selects to paint dot pattern or Graphics Mode.When wherein painting dot pattern, display module
6 positions showing current test pencil and the contact point of handwriting pad 2；During Graphics Mode, there is historical record function, show it simultaneously
Front test pencil and the position of the contact point of handwriting pad 2, reach the purpose of drawing.
S4: determine the position contacting with handwriting pad 2 by test pencil.
S5: pwm is sent to four FETs electrically connecting with the corner on this handwriting pad 2 respectively by control module 5
Ripple, alternately switches the connection of same cornerwise two FETs, so that same cornerwise two FETs is passed through constant
Electric current；Control voltage collection simultaneously and the electronic switch of amplification module, make low potential point be located on the diagonal of conducting；
S6: the electrical potential difference between test pencil and low potential is amplified by voltage acquisition and amplification module 4, respectively obtains two electricity
Pressure value v1 and v2.
S7: this two magnitudes of voltage are converted to by digital quantity by the analog-digital converter of control module 5.
S8: by control module 5 Quick Acquisition and be calculated multiple digital quantity magnitude of voltage v1 in same contact point with
v2.
S9: calculate the arithmetic average of multiple v1 and multiple v2 respectively.
S10: call the magnitude of voltage of holder storage and the mathematics corresponding relation of actual coordinate value, obtain corresponding to v1 and v2
Actual coordinate value x and y.
S11: judging present mode for painting dot pattern or Graphics Mode, if painting dot pattern, then entering step s12, no
Then it is directly entered step s13.
S12: judge whether the value of x and y changes, if YES then first initializing to display module 6, clear to display screen
Screen, and enter step s13；Otherwise it is directly entered step s13.
S13: the value of x and y is sent and shows to display module 6, and be back to step s4.
Further, in step s13, in the display screen of display module 6, the value according to x and y goes out to work as by text importing
The quadrant that front contact point is located.
The present invention illustrates the concrete technical scheme of the present invention further by following examples.
Embodiment one:
In the present embodiment one, control module adopt k60 chip, have four control ports pwm1, pwm2, pwm3 with
pwm4.K60 chip is the armcortex m4 family chip of high-performance, low-power consumption, and chip internal has integrated 16 ad, clock
Frequency is high, fast operation.The data operation ability of k60 is strong, and operation processing speed is fast and low in energy consumption, meets design requirement.
Handwriting pad: for copper-clad plate, the position at its four angles is respectively a, b, c, d.
Mos tube module: refer to Fig. 8, it is the circuit diagram of the mos tube module of the present embodiment, it include four mos pipe and
Its drive circuit.Four mos manage all using high speed n-channel enhancement mode mosfet pipe irf3205.Wherein, the grid of mos pipe q1 connects
The output end of its drive circuit, the input of this drive circuit terminates control port pwm1 of control module, and the drain electrode of q1 connects power supply
The source electrode of the output voltage+vary of module, q1 meets the position a of handwriting pad；The grid of mos pipe q2 connects the output of its drive circuit
End, the input of this drive circuit terminates control port pwm2 of control module, the drain electrode of q2 connect the output voltage of power module+
The source electrode of vary, q1 meets the position b of handwriting pad；The grid of mos pipe q3 connects the output end of drive circuit, the input of this drive circuit
Control port pwm3 of termination control module, the grounded drain of q3, the source electrode of q3 meets the position b of handwriting pad；The grid of mos pipe q4
Connect the output end of drive circuit, the input of this drive circuit terminates control port pwm4 of control module, the grounded drain of q4, q4
Source electrode meet the position d of handwriting pad.I.e. a and b of handwriting pad is high voltage, c and d is low potential point.The driving of each mos pipe
Circuit includes pnp triode s8550 and Npn triode s8050.When control port is for high level, npn pipe s8050 turns on, electricity
Forming path between source 12v and ground, producing electric current, the reverse-biased conducting of emitter-base bandgap grading of pnp triode s8550, thus drive mos pipe to lead
Logical, conversely, when control port is for high level, npn pipe s8050 ends, the not reverse-biased cut-off of emitter-base bandgap grading of pnp pipe s8550, mosfet
Pipe ends.
Voltage acquisition and amplification module: refer to Fig. 9, it is the circuit with amplification module for the voltage acquisition of the present embodiment
Figure, it includes electronic switching circuit and amplifying circuit.Electronic switching circuit adopts analog switch device 5a23157.In this reality
Apply in example, 5a23157 uses four ports: in2, no2, nc2 and com2, remaining is vacant.Wherein, in2 is control signal
Input, is electrically connected with control port pwm3 of control module；No2 and nc2 is to select end, and no2 is electrically connected with the position c of handwriting pad
Connect, nc2 is electrically connected with the d of handwriting pad, that is, no2 and nc2 is the voltage of low potential point；Com2 is output end, itself and amplifying circuit
Negative input electrical connection.The level of in2 is consistent with this pwm3, and when pwm3 is high level, diagonal switches to a and c conducting,
Now control the voltage that the voltage that com2 exports is point no2, that is, this electronic switching circuit is the point selecting low potential.Amplifying circuit
Using double operational lm358, it is second amplifying circuit, including the first operational amplifier and the second operational amplifier.First amplifier
Positive input connect and electrically connect with test pencil, negative input is electrically connected with electronic switching circuit com2, realizes differential amplification；Put
Voltage after big sends to the ad converter of control module after the second amplifier amplifies further again.Control analog switch device
The switching rate of part is consistent with fet switch speed, so that the negative input end of the first operational amplifier is always on covering
Potential minimum end on copper coin.
Power module: refer to Figure 10, it is the circuit diagram of the power module of the present embodiment.The dc/dc with two-way turns
Change, primary voltage+12v is depressured by first via dc/dc by adjustable voltage stabilizing chip lm2576t-adj, then is connect by pull-up resistor
The drain electrode of mos pipe, as drain electrode end power supply to mos pipe output constant current；Second road dc/dc is by adjustable voltage stabilizing chip
Primary voltage+12v is depressured by lm2576t-adj, then through linear voltage stabilization chip asm1175 by voltage voltage stabilizing to 5v, then warp again
Cross another linear voltage stabilization chip asm1175 by voltage voltage stabilizing to 3.3v.Wherein 5v be for control module 5 and voltage acquisition with
The amplifying circuit of amplification module 4 is powered, and 3.3v is that the electronic switching circuit for voltage acquisition and amplification module 4 is powered.Institute
To be repeatedly depressured and voltage stabilizing, it is because that linear voltage stabilization chip conversion ratio is relatively low, directly 12v being depressured to required voltage can make
Excess loss increases.
Display module: using oled12864 Liquid Crystal Module, oled12864 is the oled monochrome of 128 × 64 row dot matrix, word
Symbol, image display module 6.Its interface circuit and operational order are simple, have 8 bit parallel data interfaces, display function is powerful, point
Resolution is sufficiently high, and effect is fine and smooth, and power consumption is very small.
The circuit total figure of the present embodiment is as shown in figure 11.
The main program flow of control module is as follows:
(1) initialization analog-to-digital conversion device, timer and display module.
(2) export 4 road pwm ripples, control two groups of mos tube module switching handwriting pad diagonally to turn on, control electronic cutting simultaneously
Close circuit switching low potential point, same position is gathered respectively to obtain with two magnitudes of voltage.
(3) by amplifying circuit and analog-digital converter, the voltage of collection is amplified and analog-to-digital conversion process.
(4) magnitude of voltage is converted to by coordinate value according to the corresponding relation of voltage and coordinate.
(5) by the coordinate of display module display reality.
The test process of the hand-written drawing board of one of the present embodiment is as follows with result:
Constitute block diagram according to system, touched with test pencil, rule and drawn circle, shown by observing ammeter and oled,
Record various data, wherein oled is shown as four-quadrant and shows.As shown in figure 12, it is the test schematic diagram of the present invention.
Measuring point data table is as follows:
This test result shows: in measured zone, error 1mm-3mm, it is possible to achieve the locating and displaying of degree of precision.
Embodiment two:
In the present embodiment two, control module using stm32 series mcu be 32 bands 64 based on arm core or
The microcontroller of 128k byte flash memory, has four control ports pwm1, pwm2, pwm3 and pwm4.Processing speed is fast, precision
Height, resource is numerous.Suitable the system needs are had to measure 12 built-in adc of external signal.And this chip power-consumption is low, this is
Very big advantage.
Handwriting pad: for copper-clad plate, the position at its four angles is respectively a, b, c, d.
Mos tube module: refer to Figure 13, it is the circuit diagram of the mos tube module of the present embodiment, it includes four mos pipes
And its drive circuit.Four mos manage all using high speed n-channel enhancement mode mosfet pipe irf3205.FET irf3205 has
There are extremely low conduction impedance and quick switching rate, extremely low conduction impedance can mate the minimum resistance of handwriting pad, quickly
Switching rate can meet the requirement of continuous switching diagonal conducting.Simultaneously as voltage-controlled property device, gate turn-on control electric current
Minimum, reduce power consumption.Wherein, the grid of mos pipe q1 connects the output end of its drive circuit, the input termination control of this drive circuit
Control port pwm1 of molding block, the drain electrode of q1 meets the output voltage+vary of power module, and the source electrode of q1 connects the position of handwriting pad
a；The grid of mos pipe q2 connects the output end of its drive circuit, and the input of this drive circuit terminates the control port of control module
The drain electrode of pwm2, q2 meets the output voltage+vary of power module, and the source electrode of q1 meets the position b of handwriting pad；The grid of mos pipe q3
Connect the output end of drive circuit, the input of this drive circuit terminates control port pwm3 of control module, the grounded drain of q3, q3
Source electrode meet the position c of handwriting pad；The grid of mos pipe q4 connects the output end of drive circuit, the input termination control of this drive circuit
Control port pwm4 of molding block, the grounded drain of q4, the source electrode of q4 meets the position d of handwriting pad.I.e. a and b of handwriting pad is height
Potential point, c and d is low potential point.The drive circuit of each mos pipe includes pnp triode s8550 and Npn triode s8050.
When control port is for high level, npn pipe s8050 turns on, and forms path between power supply 12v and ground, produces electric current, pnp tri- pole
The reverse-biased conducting of emitter-base bandgap grading of pipe s8550, thus driving mos pipe to turn on, conversely, when control port is for high level, npn pipe s8050
Cut-off, the not reverse-biased cut-off of emitter-base bandgap grading of pnp pipe s8550, mosfet pipe ends.
Voltage acquisition and amplification module: refer to Figure 14, it is the circuit with amplification module for the voltage acquisition of the present embodiment
Figure, it includes electronic switching circuit, amplifying circuit and voltage follower.Electronic switching circuit adopts analog switch device
5a23157.In the present embodiment, 5a23157 uses four ports: in2, no2, nc2 and com2, and remaining is vacant.Wherein,
In2 is control signal input, electrically connects with control port pwm3 of control module；No2 and nc2 are to select end, no2 with hand-written
The position c electrical connection of plate, nc2 is electrically connected with the d of handwriting pad, and that is, no2 and nc2 is the voltage of low potential point；Com2 is output end,
It is electrically connected with the negative input of amplifying circuit.The level of in2 is consistent with this pwm3, and when pwm3 is high level, diagonal is cut
Shift to a and c conducting, now control the voltage that the voltage that com2 exports is point no2, that is, this electronic switching circuit is to select low potential
Point.Amplifying circuit adopts double operational lm2904, is second amplifying circuit, including the first operational amplifier and the second operation amplifier
Device.The positive input of the first amplifier is connect and is electrically connected with test pencil, and negative input is electrically connected with electronic switching circuit com2, real
Existing differential amplification.Voltage follower includes the 3rd operational amplifier, and its voltage after amplifying amplifying circuit is sent directly to control
The ad converter of molding block.Control the switching rate of analog switch device consistent with fet switch speed, so that the
Potential minimum end in the always on copper-clad plate of negative input end of one operational amplifier.Amplify the small electric of output on handwriting pad
Pressure, enables ad to collect accurate data, improves precision.And difference channel low noise, suppresses temperature drift, power consumption
Low.
Power module: Figure 15 please be participate in, it is the circuit diagram of the power module of the present embodiment, it has the dc/dc of two-way
Conversion, primary voltage+12v is depressurized to 1.21v by adjustable voltage stabilizing chip lm2576t-adj by first via dc/dc, then by upper
Pull-up resistor connects the drain electrode of mos pipe, as drain electrode end power supply to mos pipe output constant current.Access circuit using high-power small resistor to draw
High current, produces approximate constant-current source.Estimated, copper-clad plate resistance value is less than 10m ω, can be approximately zero compared with 1 ω resistance.This
Method can for copper-clad plate provide high current approximate constant-current source it is adaptable to little resistance cover copper hand drawing board system.Mathematical analysis is as follows:
I=v/r, when r < < when 1, di/dr=i/r^2, so electric current is basically unchanged for the rate of change of r, can be considered constant-current source.
Primary voltage+12v is depressurized to 7v by adjustable voltage stabilizing chip lm2576t-adj by the second road dc/dc, then through linear voltage stabilization core
Piece asm1175 by voltage voltage stabilizing to 5v, then passes through another linear voltage stabilization chip asm1175 again by voltage voltage stabilizing to 3.3v.
Wherein 5v is that the amplifying circuit for control module 5 and voltage acquisition and amplification module 4 is powered, 3.3v be for voltage acquisition with
The electronic switching circuit of amplification module 4 is powered.It is reliable that power module adopts lm2596 switch integrated voltage-stabilized chip to provide for system
Power supply, high conversion efficiency.Reduce power consumption compared with congenerous linear stabilized power supply.Lm2596 series is 3a electric current output buck
Switching mode integrated voltage-stabilized chip, has perfect protection circuit, current limit, Thermal shutdown circuit etc..Only need few peripheral device
Part just may make up efficient mu balanced circuit.Meet the power reguirements of circuit in order to significantly reduce power consumption, by 12v direct current simultaneously
Source is converted into 12v, 1.21v, 7v respectively by lm2596 switching power circuit, then with linear voltage stabilization chip lm1117-5.0 by 7v
It is converted into 5v.This circuit is low power dissipation design, by capacitor filtering, also can greatly improve stability of power supply.Why carry out many
Secondary step-down and voltage stabilizing, are because that linear voltage stabilization chip conversion ratio is relatively low, directly 12v being depressured to required voltage can make excess loss
Increase.
Display module: using oled12864 Liquid Crystal Module, oled12864 is the oled monochrome of 128 × 64 row dot matrix, word
Symbol, image display module.Its interface circuit and operational order are simple, have 8 bit parallel data interfaces, display function is powerful, point
Resolution is sufficiently high, and effect is fine and smooth, and power consumption is very small.
The main program of control module is as follows:
(1) by the analog-digital converter of control module, timer and display module initialize, set pwm ripple frequency with
Dutycycle.
(2) control instruction according to user selects to paint dot pattern or Graphics Mode.When wherein painting dot pattern, display module
Only show the position of current test pencil and the contact point of handwriting pad；During Graphics Mode, there is historical record function, before showing simultaneously
Test pencil and the position of the contact point of handwriting pad, reach the purpose of drawing.
(3) determine the position contacting with handwriting pad by test pencil.
(4) pass through control module and send pwm ripple to four FETs electrically connecting with the corner on this handwriting pad respectively,
Alternately switch the connection of same cornerwise two FETs, make same cornerwise two FETs pass through constant electricity
Stream；Control voltage collection simultaneously and the electronic switch of amplification module, make low potential point be located on the diagonal of conducting.
(5) pass through the electrical potential difference that voltage acquisition and amplification module amplify between test pencil and low potential, respectively obtain two electricity
Pressure value v1 and v2.
(6) this two magnitudes of voltage are converted to by digital quantity by the analog-digital converter of control module.
(7) pass through control module Quick Acquisition and be calculated multiple digital quantity magnitude of voltage v1 in same contact point with
v2.
(8) calculate the arithmetic average of multiple v1 and multiple v2 respectively.
(9) call the magnitude of voltage of holder storage and the mathematics corresponding relation of actual coordinate value, obtain corresponding to v1 and v2
Actual coordinate value x and y.
(10) judging present mode for painting dot pattern or Graphics Mode, if painting dot pattern, then entering step (11), no
Then it is directly entered step (12).
(11) judge whether the value of x and y changes, if YES then first initializing to display module, to display screen cls,
And enter step (12)；Otherwise it is directly entered step (12).
(12) value of x and y is sent and show to display module, and be back to step (3).
The test result of the present embodiment is as follows:
| Measured value (mm) | (0,0) | (-5,-5) | (5,-5) | (10,10) | (15,5) | (-25,15) | (-20,-20) | (35,25) |
| Actual value (mm) | (0,0) | (-4,-4) | (5,-4) | (10,11) | (14,6) | (-24,17) | (-19,-19) | (34,28) |
| Error amount (mm) | 0 | -1 | -1 | 1 | 2 | 3 | 1 | 3 |
Data above shows: in measured zone, error 1mm-3mm, it is possible to achieve the locating and displaying of degree of precision.
The design is by control module (built-in high-speed AD converter), power module, voltage acquisition and amplification module, mos
Tube module, display module constitute a handwriting pad coordinate positioning.This alignment system can be realized accurately showing that contact is sat
Mark, error is less than 5mm.Control module adopts data matching scheduling algorithm, and then enables contact motion tracking and graphing, book
Write the functions such as word.The ultimate resolution that the design reaches, between 1～3mm, is simultaneously achieved low power dissipation design.
The above is only the preferred embodiment of the present invention it is noted that above-mentioned preferred embodiment be not construed as right
The restriction of the present invention, protection scope of the present invention should be defined by claim limited range.For the art
For those of ordinary skill, without departing from the spirit and scope of the present invention, some improvements and modifications can also be made, these change
Enter and retouch also to should be regarded as protection scope of the present invention.
Claims (9)
1. a kind of hand-written drawing board it is characterised in that: include power module, handwriting pad, test pencil, mos tube module, voltage acquisition with
Amplification module, control module and display module；
Described power module is electrically connected with described control module, constant current source module and voltage amplification module；
Described handwriting pad is copper-clad plate；
Described mos tube module includes four mos pipes and the drive circuit with input and output end；The source of this four mos pipes
Pole is respectively correspondingly electrically connected with four angles of this handwriting pad, and the drain electrode of two on diagonal mos pipe connects power supply and ground respectively；
Wherein on handwriting pad, the position of the grounded drain of mos pipe is low potential point；The input of described drive circuit and control module
Control port electrically connects, and output end is electrically connected with the grid of mos pipe；
Described voltage acquisition and amplification module include electronic switching circuit and amplifying circuit；Described electronic switching circuit has two
Select end, a control signal input and an output end；Described two selection ends are electrically connected with two low potential points respectively；
Described control signal input port is electrically connected with control module；Described output end is electrically connected with the input of amplification module；Described
Amplification module is differential amplifier circuit, has a normal phase input end, an inverting input and an output end；Described positive
Input is electrically connected with test pencil, and described inverting input is electrically connected with the output end of electronic switching circuit；Described output end and control
Molding block electrically connects；
Described control module includes analog-digital converter and holder；This holder has the mathematics pair of magnitude of voltage and actual coordinate value
Should be related to, it is obtained by experimental data in advance；
Described display module receives the signal of control module, the contact position with test pencil on display handwriting pad；
When test pencil touches handwriting pad, described control module is switched fast two groups of diagonal of handwriting pad by mos tube module
Conducting, switches electronic switching circuit with identical switching rate simultaneously, makes the output end of electronic switching circuit always on hand-written
The low potential point of plate；Described voltage acquisition gathers the voltage difference of test pencil and low potential with amplification module and amplifies；Described modulus turns
This voltage conversion is obtained two digital voltage values by parallel operation；Described control module calls magnitude of voltage and reality stored by holder
The mathematics corresponding relation of coordinate value, magnitude of voltage is converted to actual coordinate, and sends and show to display module.
2. a kind of hand-written drawing board according to claim 1 it is characterised in that: this control module also includes a timer,
The break-make that pwm ripple controls mos pipe is exported to described mos pipe by this timer.
3. a kind of hand-written drawing board according to claim 2 it is characterised in that: described power module includes two groups of dc/dc
Conversion, the conversion of one of which dc/dc is powered to mos tube module after adjustable voltage stabilizing chip is by power voltage step down；Another group of dc/
Dc conversion is powered with amplification module to control module with voltage acquisition after linear voltage stabilization successively respectively.
4. a kind of hand-written drawing board according to claim 3 it is characterised in that: the display screen of described display module is divided into
Four quadrant areas, it obtains the signal of control module, by the place quadrant of the current contact point of text importing.
5. a kind of display methods of hand-written drawing board is it is characterised in that comprise the following steps:
Step one: by the mathematics corresponding relation of the holder stored voltage value of control module and actual coordinate value, it is by advance
Experimental data obtains；
Step 2: by the analog-digital converter of control module and display module initialization；
Step 3: determine the position contacting with handwriting pad by test pencil；
Step 4: alternately switching two cornerwise constant current source modules, two magnitudes of voltage at contact point are measured by test pencil；
Step 5: this two magnitudes of voltage are amplified by voltage amplification module；
Step 6: this two magnitudes of voltage are converted to by digital quantity v1 and v2 by the analog-digital converter of control module；
Step 7: call the magnitude of voltage of holder storage and the mathematics corresponding relation of actual coordinate value, obtain corresponding to v1 and v2
Actual coordinate value x and y；
Step 8: the value of x and y is sent and shows to display module, and be back to step 3.
6. a kind of hand-written drawing board according to claim 5 display methods it is characterised in that:
In step 2, the timer initialization of control module sets the frequency of pwm ripple；
In step 4, control module sends pwm ripple to four FETs electrically connecting with the corner on this handwriting pad respectively,
Alternately switch the connection of same cornerwise two FETs.
7. a kind of hand-written drawing board according to claim 6 display methods it is characterised in that: in step 6 and step 7
Between, further comprise the steps of: v1 and v2 of repeated detection same position, and calculate its mean value.
8. a kind of hand-written drawing board according to claim 7 display methods it is characterised in that:
Between step 2 and step 3, the control instruction according to user selects to paint dot pattern or Graphics Mode；
Between step 7 and step 8, judgment model is to paint dot pattern or Graphics Mode, if painting dot pattern, sentences further
Whether disconnected coordinate value changes, if changing, display module being initialized, if not changing, being directly entered step 8；If drawing
Pattern, then be directly entered step 8.
9. a kind of hand-written drawing board according to claim 8 display methods it is characterised in that: in step 8, aobvious
Show that in the display screen of module, the value according to x and y goes out, by text importing, the quadrant that current contact point is located.
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| CN104166478A (en) * | 2014-08-12 | 2014-11-26 | Tcl通讯（宁波）有限公司 | Touch positioning method and device of touch screen |
| CN107450787B (en) * | 2017-09-04 | 2023-08-04 | 深圳市千分一智能技术有限公司 | Active capacitive touch module and intelligent hand-painted plate |
| CN114281204B (en) * | 2021-12-09 | 2023-11-03 | 深圳市广和通无线通信软件有限公司 | Method, device, equipment and storage medium for touch recognition of resistive touch screen |
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| JP2000029586A (en) * | 1998-07-08 | 2000-01-28 | Sharp Corp | Handwriting input device |
| JP2001014100A (en) * | 1999-06-28 | 2001-01-19 | Nyuuton:Kk | Handwriting input device and writing way learning device |
| CN202904516U (en) * | 2012-06-05 | 2013-04-24 | 苏州鼎雅电子有限公司 | Multifunctional handwriting drawing board device |
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| JP2000029586A (en) * | 1998-07-08 | 2000-01-28 | Sharp Corp | Handwriting input device |
| JP2001014100A (en) * | 1999-06-28 | 2001-01-19 | Nyuuton:Kk | Handwriting input device and writing way learning device |
| CN202904516U (en) * | 2012-06-05 | 2013-04-24 | 苏州鼎雅电子有限公司 | Multifunctional handwriting drawing board device |
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