TW201115448A - Multi-touch measuring method for resistive touch panel - Google Patents

Abstract

A multi-touch measuring method includes the following steps. Measure currents flowing through a first and a second thick film resistors to recognize present touch operations as a single-touch interaction or a multi-touch interaction and to measure the distance between two touch points under a multi-touch scenario. Measure terminal voltages of the first and the second thick film resistors when an external voltage is applied to either of them to detect relative positions of the two touch points.

Description

201115448 VI. Description of the Invention: [Technical Field] The present invention relates to a multi-touch detection method for a resistive touch panel. [Prior Art] FIG. 1 is a schematic view of an internal component of a conventional resistive touch panel. Generally, the touch panel is divided into a capacitive touch panel and a resistive touch panel. Among them, the resistive type touch panel is formed by stacking the X layer board 102 and the Y layer board 104 up and down. Both the X-layer board 102 and the γ-layer board 1〇4 are planar resistors and do not contact each other in a natural state. When the user applies a force to touch the resistive touch panel, the χ layer 1 〇 2 and the Υ layer 104 are brought into contact with each other at the corresponding contact point. For example, when the user applies a force-sensitive resistive touch panel, the point 对1 corresponding to the touch point on the γ layer board 1〇4 is in contact with the point ρ2 of the X layer board 1〇2 corresponding to the touch point. . 2 is an equivalent circuit diagram of the resistive touch panel of FIG. 1. Resistive Touch • In the equivalent circuit 202 of the board, there is an equivalent resistance RM between the X-layer board 1〇2 and the Υ layer board 1〇4. When the raft layer 1〇4 and the Χ layer board 1〇2 are in a natural state, the two are not in contact. At this time, the open layer between the enamel layer 1〇4# χ layer 1 〇 2 is regarded as an equivalent resistance between the X layer board 102 and the Υ layer board 1 () 4 having an inductive value of infinity. When the external force touches the resistive touch panel, the γ layer plate and the X layer plate 1〇2 are in contact with each other, and a path is formed therebetween, so that the resistance value of the equivalent resistance RM is much smaller than the resistance value in the natural state. In addition, the χ layer board 102 and the Y layer board 104 are planar resistors, and when the external force touches the resistive touch panel, 201115448 makes the point pi on the Y layer board 104 and the point p2 on the χ layer board 1 〇 2 contact each other. The equivalent resistance of the X-layer board 102 is the two resistances and Rx1 coupled to the point p2. The resistance values of the two equivalent resistors Rx 〇 and Rx are determined by the position of the X-layer board 102. And its resistance value only changes with the position of the 乂 coordinate of the point p2, and does not change with the position of the Y coordinate. Similarly, the equivalent resistance of the gamma layer 104 is the two resistors Ry and Ryl connected in series to the point P1. The resistance values of the two equivalent resistors RyO and Ryl are determined by the position pl of the φ position of the γ layer plate 1〇4. And the resistance values of the two equivalent resistors RyO and Ryl vary only with the position of the Υ coordinate of the point, and do not change with the position of the coordinate. In this way, when there is an external force touching the resistive touch panel, so that the point Ρ1 corresponding to the touch point on the γ layer board 1〇4 and the point Ρ2 corresponding to the touch point on the χ layer board 102 are in contact with each other, etc. The effective circuit is shown in Figure 2. However, the above-mentioned resistive touch panel generally only knows the coordinate position of the single touch, and it is difficult to perform a multi-control operation. Therefore, there is an urgent need for a simple Ludo! The _control_method is used in the hybrid control board to implement the multi-touch function. SUMMARY OF THE INVENTION The present invention provides a multi-touch side method for a resistive touch panel. Other objects and advantages of the present invention will be apparent from the technical features disclosed herein. 201115448, for the above-mentioned or some or all of the objectives or other purposes, the second embodiment of the present invention provides a multi-touch ready-to-measure square-side resistive touchpad for a resistive touch panel, at least for The multi-touch side method for generating the 帛+face resistance of the first-axis coordinate signal and the six-plane resistance of the coordinate signal for generating the second axis includes the following steps: measuring the flow through The first plane resistance or the second plane power_current is branched by the current to determine whether the current touch state is a single touch mode or a multi-touch mode _ and a multi-quench mode And in the fresh touch mode = force π voltage to _ first-plane resistance and measure the terminal voltage of the second planar resistance, or apply a voltage to the second planar resistance and measure the end of the first planar resistance The voltage is used to determine the relative position of two different pressure points. Another embodiment of the present invention provides a multi-touch detection method for a resistive touch panel. The resistive touch panel includes at least a transparent conductive layer and a gamma transparent conductive layer with a space therebetween. The transparent conductive layer has a first X side and a second side in a direction parallel to the Y-axis, and the transparent conductive layer has a first side and a first side in a parallel X-axis direction. The second gamma side 'the detection method comprises the steps of: providing a sensing voltage to the first X side and connecting a current measuring unit to the second X side, or providing a sensing voltage to the first γ side And connecting a current measuring unit to the second Yu side; when the single point touches the resistive touch panel, the current value obtained by the current measuring unit is preset as a reference current value; and comparing the current touch In the state, the measured current value measured by the measuring unit and the reference current value, wherein when the measured current value is equal to the reference current value, the current touch state is the single touch mode. And when the measured current value is greater than the reference current value, Before TOUCH state is the multi-touch mode. In an embodiment, the multi-touch detection method further includes the following steps: In the multi-touch mode, establishing a correspondence between the distance between two different touch points and the current change to obtain the current touch state. The distance between two different pressure points. Another embodiment of the present invention provides a multi-touch detection method for a resistive touch panel, the resistive touch panel including at least one space apart from each other

The X transparent conductive layer and the γ transparent conductive layer have a first X side and a second X side in a parallel Y-axis direction, and the Y transparent conductive layer is in a parallel X-axis direction Having a first Y side and a second Y side, the detecting method includes the steps of: providing a sensing voltage to the first X side and grounding the second X side and connecting a voltage measuring unit Up to the γ-side and the second γ side, or providing a sensing voltage to the γ-side and grounding the second 且 side and connecting a voltage measuring unit to the first side and the second side X side; and comparing the first threshold voltage value and the second X-side voltage value measured by the voltage measuring unit, or comparing the first threshold voltage value measured by the voltage measuring unit with the The second gamma side voltage value is used to determine the relative positions of the two different touch points. Based on the design of each of the above embodiments, by measuring the current value of the X side and the Υ side of the resistive touch panel, or the voltage values of the X side and the γ side, it can be determined whether the current 201115448 touch mode is multi-touch. And using the current and voltage measurement architecture of the (4), the distance and position relationship of the two touch points can be obtained in the two-touch mode, and the current touch behavior mode of the user is known. The above features and advantages of the invention will be apparent from the description and appended claims appended claims [Embodiment] In the detailed description of the embodiment in which the reference pattern is used in the vicinity of the present invention, it will be clearly explained in the detailed description of the embodiment of the present invention. The directional terms mentioned in the following embodiments, for example, up, down, left, right, front or back, etc. are merely directions referring to the additional drawings. Therefore, the directional term used is used to describe that it is not intended to limit the invention. 3 and 3 are block diagrams showing the implementation of an embodiment of the multi-touch detection method. The sister picking her 1G at least includes a transparent conductive layer 12 and a transparent conductive layer 14 which are spaced apart from each other, and the transparent conductive layer has a first side (Xa side) 12a and a first side (Xa side) 12a in the parallel_axis direction A second 乂 side (Xb side) 12b, and the γ transparent conductive layer has a first γ side (Ya side) 14a and a second γ side (Yb side) 141 ??? in a parallel axis direction. The transparent conductive layer 12 and the transparent conductive layer 14 can be regarded as planar resistors for respectively generating a first axial coordinate signal and a second axial coordinate signal. In FIG. 3A, the resistive touch panel 1 is connected to a power source (not shown) to provide a sensing voltage Vdd to the first side 14a, and a current measuring unit 16 to the second Y side 14b. . In FIG. 3B, the resistive touch panel 1 is connected to 201115448 to a power source (not shown) to provide a sensing voltage Vdd to the first X side 12a, and connects the current measuring unit 16 to the second side. 12b. Please refer to FIG. 4, FIG. 5A and FIG. 5B at the same time. FIG. 4 is an equivalent circuit model of the single-touch mode, and FIG. 5A and FIG. 5B are simplified two-point touch mode equivalent circuit models, wherein FIG. 5A corresponds to FIG. 3A. (The sensing voltage Vdd is applied to the first gamma side 14& and assumes that the X-axis displacements of the two touch points are the same; χ Χ 2), and FIG. 5B corresponds to FIG. 3B (the sensing voltage vdd is on the first-side 12a and assuming _pressure off γ axis displacement

Same; Y1=Y2). When there is only a single-touch point τ, the single-touch model of _ 4 knows that the current measuring unit 16 measures the current regardless of the touch position.

Iy〇 is fixed, but when the touch point is two points Τ1 and 丁2 on the Υ axis, the coordinates of the touch point T1 are (X1, Y1), and the coordinates of the touch point D2 are (Χ2, η), And assuming X1=X2, then the equivalent circuit model needs to adopt Figure 5A. At this time, the γ-axis equivalent total resistance Ry conforms to the following formula: R4 + R6 R2 + R5 + R7 From the above formula, the two-point contact pressure can be The parallel effect of the resistor is generated, so that the total resistance is decreased. The γ-effect total resistance of the two points (1) is less than the single-contact y-axis equivalent total resistance _. In other words, two points of pressure 曰

The current Iy measured by the time unit 16 will be greater than the current measured by the current level 7G 16 when the single point is touched. . In addition, as shown in the figure, when a sense is provided to the first side 12a of the resistive touch panel H), and the -current_unit 10 is connected to the second _, when the touch point is X 201115448 Two points on the axis τι and T2, the coordinates of the touch T1 are (χι, γι), the coordinates of the dust point Τ2 are (Χ2, Υ2), and when the wire is set to υι=υ2, the equivalent circuit model can be used privately. Figure 5 Β 'χ 总 总 总 ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( When the current measurement is measured, the current is 1X0. Therefore, the micro-device 18 can determine the current touch state riding mode or the multi-gate control mode by the current measurement value. Next, as shown in FIG. 5A as follows, when the pressure point is two points, how the distance between the two sides of the female is small or increased by the change of the current value. As shown in FIG. 5A, when the touch point changes from T1 to T1, or from T2 to T2, and the distance between the two points increases from d to distance d+Ad, the resistance R1 or the resistor R3 decreases and the resistance R2 decreases. Since it is increased, it is known from (Formula 1) that the γ-axis equivalent total resistance Ry (tl', t2,) becomes small. Therefore, when the distance between the two points increases, the current Iy' measured by the current measuring unit 16 is greater than the current measured by the original distance. Conversely, when the distance between the two points decreases, the current measured by the current measuring unit 16 is Iy, It will be smaller than the current Iy measured by the original distance. By measuring the change in current, a change in the distance between two different contact points can be obtained, and because of the distance between the two contact points, the current value flowing through the X transparent conductive layer 12 or the Y transparent conductive layer 14 has — Proportional relationship' Therefore, after measuring the current value, the distance between two different contact points in the current touch state can be obtained. 6A and 6B are implementation diagrams of another embodiment of the block diagram's multi-touch detection method. The resistive touch panel 10 includes at least an X transparent conductive layer 12 and a Y transparent conductive layer 14 ′ having a spacing of 201115448. The x transparent conductive layer has a first X side (Xa side) in a parallel Y-axis direction. 12& and a second X side (Xb side) 12b, and the Y transparent conductive layer has a first Y side (Ya side) 14a and a second γ side (Yb side) 14b in a parallel X-axis direction. . The X transparent conductive layer 12 and the Y transparent conductive layer η can be regarded as planar resistances which respectively generate a first axial coordinate signal and a second axial coordinate signal.

As shown in FIG. 6A, in the embodiment, the resistive touch panel 1 is connected to a power source 22 to provide a sensing voltage vdd to the first gamma side i4a, and the first Y side 14b is grounded, and a voltage The measurement unit 26 is connected to the first side 12a and the second side Xb'. The voltage measurement can be fed to the microprocessor 18 for analysis. Therefore, it can be seen from the equivalent circuit of Fig. 7A that the terminal voltage Vxa of the first side 12a and the terminal voltage Vxb of the second X side 12b are respectively:

Vxa = (Vdl-Vd2)x Vxb = (Vdl-Vd2)x K7 (R7 + R5) R6 (R6 + R4) + Vd: + Vd: (Formula 2) Therefore, as shown on the right side of Figure 7A, when two touches When the pressure points T1 and T2 have not been rotated, since the resistance R5=R7 and the resistance R4=R6 at this time, Vxa=Vxb can be obtained from the second formula. When the two contact points Ή, T2 rotate clockwise to the new contact point Ή, T2 position, because the resistance R5 decreases and the resistance increases, the second end can find that the terminal Vxa will increase, and this When the resistance R4 increases, the resistance % decreases, so that the terminal voltage Vxb is reduced by the second formula. It can be seen that when the two touch points rotate clockwise, the terminal voltage Vxa will increase and the terminal will be reduced by 11 201115448; otherwise, when the two relay points rotate counterclockwise, the terminal light b will decrease and the terminal voltage will decrease. Vxb will increase. The embodiment of FIG. 6B is similar to that of FIG. 6a except that the X side and the Y side are interchanged, and FIG. 7B is an equivalent circuit diagram of the embodiment of FIG. 6B. The terminal voltage vya and the object ten calculation method are as described above, so Re-status. ^ This is determined by the amount of (4)-γ Jingmu to the second γ-touch impedance green change, or the measured X-side relative to the second X-side impedance is repeatedly changed, and the first touch pressure point together with the second touch pressure point can be discriminated Turn clockwise or counterclockwise. • In addition, if the coordinates are taken from the figure, as shown in Figure 7 and Figure 8, the first X side (Xa side) 3⁄4 value is greater than the second side (10) side) voltage, and the two different touch points are as shown. 8Α falls into the odd coordinate quadrant (first and third quadrant), and when the voltage is on the first-X side (the Xa purchase end value is smaller than the second side (10) side), the two different touch points are as shown in Fig. 8Β. Falling into the even-numbered quadrant (second and fourth quadrants), taking Figure 6Β and 7Β as examples, the first γ-side (Ya-side) voltage is greater than the second γ-side (Yb-side), and the two different touch points are shown in Figure 8A. The figure falls into an odd number, her quadrant area, and when the first gamma side (Ya side) voltage value is smaller than the second Y side (10) side) voltage value 'two different touch pressure points fall into the even coordinate quadrant area as shown in FIG. 8B By measuring the terminal voltage value of the X side and the second X side, or the terminal voltage values of the first Y side and the second Y side, the coordinate quadrant position where the two touch points fall can be known. Therefore, based on the design of each of the above embodiments, it is possible to determine whether the target touch mode is multi-point by measuring the current value of the X side and the γ side of the resistive touch panel or the voltage values of the χ side and the γ side. Touch, and with the simple current and 12 201115448 voltage measurement architecture, the distance and position relationship of the two relay points can be obtained in the two control modes, and the current touch behavior mode of the user is known. Therefore, the simple measurement architecture of the above embodiments can provide a multi-touch function of the resistive touch panel. FIG. 9 is a flowchart of a multi-touch method according to an embodiment of the present invention. In an embodiment, the method may include at least partial steps as follows:

Step S10 · Start.

StepS20: providing-sensing voltage to the first (10) and connecting the current measuring unit to the second X side, or providing a sensing voltage to the first side and connecting a current measuring unit to the second side .

Step S30: When the single point touches the resistive touch panel, the current value obtained by the current measuring unit is preset as a reference current value.

Step S4G: Compare the measured current measurement unit in the current touch state - measure the current value of the current scale, and t measure the current value of the f flow value is equal. 'The current touch state is the single touch mode. And the equivalent current value is greater than the reference current slope, and the target_control_ is more _thief type. : In multi-touch mode, the distance between two current touch states can be obtained by measuring the change of current. ",

Step S50: providing a sensing voltage to the first side and the second side and connecting the voltage measuring unit to the first side and the second side, or raising the voltage to the first side The side connects the second gamma side ground-voltage measurement element to the first X side and the second side. , 13 201115448

Step S60: Comparing the first χ side voltage value measured by the voltage measuring unit with the first value and the second γ side voltage value measured by the first value or the comparison voltage (4) unit. To determine the relative position of two different touch points

Step S70 ·· End. However, the above is only the preferred embodiment of the present invention, and the scope of the present invention is not limited thereto, that is, the application of the present invention is as follows: • Simple equivalent changes made by the description of the invention And Xiudu are still within the scope of the patent of the present invention. In addition, all of the objects or advantages or features of the present invention are not to be construed as being limited by the scope of the invention. Further, the abstract sections and headings are only used to assist in the search for patent documents and are not intended to limit the scope of the invention. [Simple diagram of the diagram] The ® ® 1 is a schematic diagram of the internal components of the resistive touch panel. 2 is an equivalent circuit diagram of the resistive touch panel of FIG. 1. 3A and 3B are block diagrams showing an implementation architecture of an embodiment of a multi-touch detection method. FIG. 4 is an equivalent circuit model of the single touch mode, and FIG. 5A and FIG. 5B are simplified two-point touch mode equivalent circuit models. 6A and 6B are block diagrams showing an implementation architecture of another embodiment of a multi-touch detection method. 201115448 FIG. 7A is an equivalent circuit diagram of the embodiment of FIG. 6A, and FIG. 7B is an equivalent circuit diagram of the embodiment of FIG. 6B. 8A and 8B are schematic views showing coordinates of two different contact points. FIG. 9 is a flowchart of a multi-touch detection method according to an embodiment of the present invention. [Main component symbol description]

10 resistive touch panel 12 X transparent conductive layer 12a first X side 12b second X side 14 Y transparent conductive layer 14a first Y side 14b second Y side 16 current flow measuring unit 18 microprocessor 22 power supply 26 voltage amount Measurement unit 102 X-layer board 104 Y-layer board 202 equivalent circuit Step 10-70 Method step 15

Claims (1)

201115448 VII. Patent Application Range: 1. A multi-touch detection method for a resistive touch panel, the resistive touch panel comprising at least a first plane for generating a first axial coordinate signal a resistor and a second planar resistor for generating a second axial coordinate signal. The multi-touch detection method comprises the following steps: Measure the current flowing through the first planar resistance or the second planar resistance, and determine the current touch state as a single touch mode or a multi-touch mode and in the multi-touch mode by using a change in current a distance between the two touch points; and applying a voltage to the first planar resistance in the multi-touch mode and measuring a terminal voltage of the second planar resistance, or applying a resistance to the second planar resistance and measuring the first - The terminal voltage of the planar resistor to determine the relative position of the two different contact points. 2. The multi-control method according to claim 1, wherein the current measuring step comprises: ~ connecting the first plane resistance or the opposite sides of the second plane resistor to a power source and a current measuring unit; when the single point touches the resistive touch panel, the current value obtained by the current measuring unit is preset as a reference current value; and comparing the current measuring unit in the current touch state a measured current value and the fresh current value, wherein when the measured current value is equal to the reference current value, the current touch state is the single touch mode (four) work type, and when the current is measured When the value is greater than the s-based reference current value, the current touch-like energy can be used as the multi-touch mode 16 201115448 type 0 more includes == face _ 2 of the face _ test method, at 5 Hz multi-touch Under Plant 4, the correspondence between the distances between two different pressure points is established to obtain the distance between the two touch points in the current touch state. J 4. The method of multi-touch pre-measurement according to claim 3, wherein the rotation of the two surface points in the basin has a proportional relationship with the eight current values flowing through the first-second plane resistance. 5. The multi-touch side method described in the first aspect of the invention, the step of measuring the voltage of the terminal in the basin includes: 八: connecting the opposite sides of the first plane resistance to a power supply and grounding respectively to the λ plane The opposite sides of the resistor are connected to a voltage measurement unit, and the opposite sides of the second plane resistance are respectively connected to the power source and the ground, and the opposite sides of the α-hai plane resistance are connected to a voltage measuring unit; And comparing the individual voltage values of the two sides of the first planar resistance or comparing the two individual voltage values of the second planar resistance to determine the relative positions of the two different touch points. 6. The multi-touch detection method of claim 5, wherein the Haidi axis defines a different coordinate quadrant region along with the axis, and the first or second planar resistance The individual voltage values on both sides determine the coordinate quadrant area where the 2011 17448 and the touch point fall. 7. The multi-touch detection method of claim 2, wherein the first axis of the 5H is substantially perpendicular to the second axis. 8. The method of claim 20, further comprising the step of transmitting the current measurement values and the voltage measurement values to a microprocessor. 9 'A multi-touch detection method for a resistive touch panel, the resistive touch panel comprising at least a X transparent conductive layer and a Y transparent conductive layer spaced apart from each other, the X transparent conductive layer being parallel __ having a first X side and a second X side in the γ-axis direction, and the Υ transparent conductive layer has a first γ side and a second 丫 side in a parallel axis direction, The debt measurement method comprises the steps of: providing a sense voltage to the first side and connecting a current measuring unit to the second X side, or providing a sensing voltage to the first gamma side and a The current measuring unit is connected to the second γ side; when the single point is pressed against the resistive touch panel, the current value obtained by the current measuring unit is preset as a reference current value; and the current is compared in the current touch state. Measuring a measured current value and the reference current value, wherein when the measured current value is equal to the reference electrical output value, the target state is the single control mode, and t the measuring current When the value is greater than the reference current value, the current touch state is the multi-touch Mode. 18 201115448 10. The multi-touch detection method according to claim 9 further includes the following steps: in the multi-touch mode, establishing a distance between the two different touch points and the current The corresponding relationship of the changes to obtain the distance between the two different touch points in the current touch state. 11. The multi-touch detection method of claim 1, wherein the distance between the two touch points has a proportional relationship with a current value flowing through the first or second planar resistance. 12. A multi-touch detection method for a resistive touch panel, the resistive touch panel comprising at least a χ transparent conductive layer and a Y transparent conductive layer, each of which is electrically conductive Parallel-cocoa has an opposite first side and a second side, and the gamma transparent conductive layer has (-)------------- The method includes the following steps: -f Μ η μ scale - Χ side and ground the second Χ side and will fry the plant to the first side and the second side, or provide - sense ^ = to the mail-丫 side and Connecting the second γ side grounding county to the first X side and the first side; the early side voltage value and the second γ side electric quantity=the first χ side voltage value measured by the measurement list and the One side of the light value, or comparing the first-gamma position pressure value measured by the double-measurement single-tip, to determine the relative position of two different touch points. 19 201115448 13. The multi-touch as described in claim 12 Control detection method 'When the first X-side voltage value is greater than the second X-side voltage value or the first Y-side voltage value is greater than the first Y-side voltage value of s, the two different The pressure point falls into the first coordinate area, and when the first X-side voltage value is less than the second-side voltage value or the first γ-side voltage value is less than the second γ-side voltage value, the two different touch points Falling into the second coordinate area, and the first coordinate area is different from the second coordinate area. • M. A multi-touch detection method for a resistive touch panel, the resistive touch panel comprising at least a X transparent conductive layer and a γ transparent conductive layer spaced apart from each other, the X transparent conductive layer being parallel a gamma axis direction having opposite - a first X side and a second X side, and the Υ transparent conductive layer has a relative - first Υ side and a second γ side in a parallel 乂 axis direction, the debt The measuring method comprises the steps of: connecting the first X side to a power source and grounding the second side and connecting a voltage 1: meter 7G to the first γ side and the second γ side, or The first side is connected to a power source and the second γ side is grounded and a voltage measuring unit is connected to the first X side and the second side, wherein the touch state is a two-touch mode and When the H touch point is the second touch point, and the X-axis coordinate or the γ-axis coordinate of the first and the first touch point is the same, the first touch point is formed between the first touch point and the first touch point a first impedance, the first contact point and the power source form a second impedance, the second relay point and the ground end form a third impedance, Forming a fourth 20 201115448 impedance between the first contact point and the first side or the first side, forming a fifth between the first contact point and the second x side or the second γ side Forming a sixth impedance between the impedance, the second contact point and the first X side or the first side, and forming a first between the second touch point and the second X side or the second side And determining an impedance partial pressure change of the first side of the first side relative to the second side of the first X side, and measuring the impedance partial pressure change of the first X side with respect to the second X side, thereby determining the first touch pressure The point rotates clockwise or counterclockwise along with the second point of pressure. twenty one