WO2004077679A1

WO2004077679A1 - Method and apparatus for decoding a key matrix

Info

Publication number: WO2004077679A1
Application number: PCT/SG2003/000041
Authority: WO
Inventors: Swee Hock Alvin Lim; Jasmeet Singh Narang
Original assignee: Infineon Technologies Ag
Priority date: 2003-02-28
Filing date: 2003-02-28
Publication date: 2004-09-10

Abstract

A data input apparatus is proposed in which an integrated circuit ahs pins electrically connected to respective conductive lines 0, 1, 2, 3, 4, 5, and a keypad includes keys 6, 16, 116, which when depressed connect multiple ones of the lines. The integrated circuit performs a series of scan steps in which the voltages of one or more of the pins are fixed and the voltages of the other pins are measured. In contrast to known methods, the keypad includes keys 16, 116 which when operated each connect more than two of the lines. For example, there may be keys 16 which connect two pairs of lines together pairwise. The invention makes it possible for the voltages monitored by the pins to be modified in a way which is different from any of the voltage modifications which are possible using any one of the conventional keys 6. Thus, if the proposed keys 16, 116 are used in combination with the known keys 6, then a keyboard is provided having an increased total number of keys. This is achieved without the number of pins being increased.

Description

METHOD AND APPARATUS FOR DECODING A KEY MATRIX

Field of the invention

The present invention relates to detecting that a user has operated one or more keys.

Background of Invention

Figs. 1 to 3 illustrate a known technique used by an integrated circuit to detect whether one of a number of keys of a keypad has been operated. In the known technique the key is "operated" by depressing the key, as discussed below, but the term "operated" is used in this document in a wider sense, to include any actuation caused by a user including moving the key.

The known technique is performed by an integrated circuit which uses six pins numbered 0 to 5. Each of the pins of the integrated circuit is connected to a respective line on a printed circuit board, and these lines are arranged in a matrix of rows and columns shown in Fig. 1 , where the reference numerals 0 to 5 indicate horizontal and/or vertical portions of the lines connected to the corresponding pins.

Each of the dots 6 indicates a respective key, located on the intersection of one of the columns and one of the rows. A typical intersection between two of the lines 8, 9 is as shown in Fig. 2, and includes a portion 11 where the two lines are arranged in a spiral configuration without actually touching. The line 8 may be any of the lines extending in the vertical direction in Fig. 2, while the line 9 may be any of the lines extending horizontally. Figs. 3(a) and 3(b) are respectively a side view and a bottom view of a key 6 which is arranged over this spiral portion 11. The key 6 includes a circular conductive portion 13 on its lower surface which is in register with the portion 11. When the key 6 is not depressed the conductive area 13 is spaced from the lines 8, 9, but when the key is depressed, the circular area 13 forms an electrical connection between the two lines 8, 9 in the region 11.

When exactly one key is depressed, the integrated circuit is able to detect this fact as follows. The integrated circuit is operative to fix any of the lines to be at a first voltage level or at a second voltage level, referred to respectively as a "driving voltage" (e.g. voltage low) and a "preparation voltage" (e.g. voltage high). The integrated circuit initially sets all of the lines to the preparation voltage (high). Then for each of the lines in turn the integrated circuit sets that line only to the driving voltage (low) while detecting the voltage on the other lines. If while that first one of the lines is set to the driving voltage, any second one of the lines adopts the driving, this indicates that the key which connects those two lines has been depressed. As mentioned below, it is not necessarily to monitor all A?-1 of the undriven lines at all times. Referring to Fig. 1 again, the lines extending in the vertical direction may be successively set to the driving voltage, and each of the horizontal lines which have an intersection with that vertical line is monitored.

As shown in Fig. 1 , there is exactly one key 6 for every combination of two different lines, i.e. 15 in total. More generally, if the number of lines (pins) is n, the number of keys which can be detected by this method is ⁿC₂, i.e. n(n-1)/2. The lines are driven using a finite state machine employing /? scan cycles, in which, as explained above, each scan cycle consists of driving a respective one of the lines and scanning the voltage on the rest of the lines.

In one form of this technique, after finding that a key has been pressed, a confirmation of that result is performed in the next scan cycle. In this manner, every two scan cycles one key is detected and confirmed. The control logic performed on-chip by the integrated circuit in this case is shown in Fig. 4. Fig. 4 employs a variable x which during a scan cycle successively takes values from 0 to n-1 (in any order). Starting at step 17, the integrated circuit drives line x to the driving voltage while other lines are set to the preparation voltage and then allowed to float. In step 18 the voltages on the x lines x+1 , x+2, ..., n are measured (note that it is not necessary to monitor the voltages on all the lines, since during the entire scan cycle every combination of two lines will be tested to see whether they are connected).

In step 19 it is determined whether the voltage on any of the monitored lines has changed to the driving voltage. If the result is positive, then the method proceeds to step 20 in which it is determined which key, when pressed, would given this measurement. Subsequently, in step 21 it is determined whether, on the previous scan cycle, the fact that this key was being pressed was registered. If not (i.e. if this is the first scan cycle in which it has been noted that this key is being pressed), then in step 22 this fact is registered.

Alternatively, if the determination in step 21 is positive (i.e. the fact that the key is pressed has been noted in the previous scan cycle also), the method proceeds to step 23 in which the key press it confirmed. Following either of steps 22 or 23 (or if the result in step 19 was negative), the method proceeds to step 24 in which the value of x is changed. After step 24, the method returns to step 17. Therefore the method is repeated continuously, scanning though x values 0 to n-1 (though not necessarily in that order).

Whenever a positive confirmation is achieved in step 23, a confirmation signal is generated which triggers a separate process not shown in Fig. 4 in which the integrated circuit reacts to the confirmed key depression. For example an interrupt signal can be generated to a microprocessor which takes appropriate actions. Comparing what confirmation signals are generated in successive scan cycles allows the integrated circuit to detect new key depressions, and when keys are released. Summary of the Invention

The present invention aims to provide a new and useful method for detecting when keys have been operated.

In particular, the invention aims to provide methods in which a given number of input pins are capable of detecting the operation of more than ⁿC₂ of the keys.

In general terms, the present invention proposes that at least one key is arranged when operated to electrically connect more than two of the lines.

The invention makes it possible, when one or more of the lines are set at a driving voltage, for the voltages of the other lines to be modified, by operating the proposed new key, in a way which is different from any of the voltage modifications which are possible using any one of the conventional keys. The integrated circuit is arranged to be sensitive to such modifications, and thus recognises that the novel key has been operated. Thus, if the proposed key is used in combination with the keys of the known method, then a keyboard is provided having an increased total number of keys. This is achieved without the number of pins being increased.

Preferably, the proposed keys each form electrical connections among a number of lines which is even, and connects those lines pairwise. In one particularly preferred form of the invention, the key matrix includes at least one key which, when it is operated, is arranged to electrically connect a first pair of lines to each other and a second pair of lines to each other.

In some forms of the invention, for any given combination of a certain number of lines there is at most exactly one key. This key connects those keys pairwise when operated, and the fact that the key has been operated is determined by setting one of the lines of each pair to a driving voltage, measuring the voltages of at least the other lines of each pair (and normally other lines), and determining that the voltages of the other lines of each pair have adopted the driving voltage.

For example, suppose that there is exactly one key which, when operated, connects a first pair of lines and a second pair of lines. In this case, the fact that the key has been operated can be detected in a single step by setting a first line of each pair to the driving voltage and monitoring the voltage of the other line of each pair. The integrated circuit is arranged to detect whether the second line of each pair has assumed the driving voltage, and if so to infer that the key has been operated.

However, the invention is not limited in this respect, and in more complex embodiments it is possible to provide, for any given group of four or more lines, a plurality of keys arranged to form different respective pairwise connections among that group of lines. For example, considering four such lines, a first key may when operated connect a first of the lines to a second of the lines and a third of the lines to a fourth of the lines, while a second key may when operated connect the first of the lines to the third of the lines and the second of the lines to the fourth of the lines. If, in this example, the first and fourth lines are set to the driving voltage, then the voltage of the second and third lines will assume the driving voltage when either of the two keys is pressed, so that it can be determined that at least one of the two keys has been operated. However, if the first and third lines are now set to the driving voltage, then the monitored voltage on the second and fourth lines will be different depending upon which of the first or second keys has been operated.

More generally, for any given set of a given even number of lines, there may be a key for each possible way of connecting those lines in pairs (for example, there may be three keys for each set of four lines). In the case that the proposed keys each connect two pairs of lines, the integrated circuit preferably performs a scan cycle composed (in addition to the steps of the known method in which respective ones of the lines are driven while up to all of the other n-1 lines are monitored) of steps in each of which two of the lines are set to the driving voltage while up to all of the other n-2 lines are monitored. For example, in each step a different pair of the lines may be set to the driving value. It is highly preferable that the two lines are set to the driving values simultaneously, so that the system is not confused if two different keys are pressed at times which are different, but only very slightly spaced apart.

This concept may, however, be generalised to provide keys which are arranged, when operated, to connect more than two pairs of keys. In other words, the key may be arranged to connect, pairwise, four lines (as described above), six lines, etc. In principle, the keypad may even include a key which connects all the lines pairwise (i.e. as n/2 pairs, with the two lines of each pair being connected to each other).

According to the number of lines which are connected to each switch, the integrated circuit may use a scan cycle which includes in different scans different ones of the lines, different pairs of the lines, different triplets of the lines, and so on.

Preferably, when multiple lines are set to a diving voltage, these driving voltages are identical. This means that if a switch is operated which happens to connect those two lines, there is no shorting between the two driving voltages. However, alternatively additional circuitry may be provided to take this possibility into account, since in the case that the two driven lines are not connected to each other more information may be derived in a single scan step from multiple driving voltages than from a single one. Brief Description of The Figures

Preferred features of the invention will now be described, for the sake of illustration only, with reference to the following figures in which:

Fig. 1 illustrates schematically a known keypad arrangement; Fig. 2 illustrates an arrangement of a pair of lines in the known keypad;

Fig. 3, which is composed of Figs. 3(a) and 3(b), illustrates a key used in the known method;

Fig. 4 is a flowchart of a known method employing the keypad of Fig. 1 ; Fig. 5 illustrates a portion of a keypad which is an embodiment of the present invention;

Fig. 6 illustrates an arrangement of two pairs of lines in the keypad of Fig. 4;

Fig. 7, which is composed of Figs. 7(a) and 7(b), illustrates a key which is itself an embodiment of the invention, and which is suitable for use with the embodiment of Fig. 5;

Fig. 8 illustrates an optional keypad portion of the embodiment of Fig. 5; and

Fig. 9 illustrates a flowchart of the operation of a method which is an embodiment of the invention, and uses the keypad portion of Fig. 5 and/or Fig. 8.

Detailed Description of the embodiments

Figure 5 illustrates fifteen keys 16 of keypad according to the invention, and how these keys are arranged in relation to a matrix of lines on a printed circuit board which are electrically connected to the six pins 0, 1, ...5 of the integrated circuit. Each of these lines includes horizontal and vertical portions, and all lines are labelled by a reference numeral which is the pin to which the line is connected. It will be seen that each key 16 is at an intersection portion 111 of four lines, and there is one key for each combination of four lines, i.e. ⁿC4=15 keys in all.

Figure 6 indicates a typical intersection portion 111 of four lines marked 28, 29, 38, 39. For example, the two lines 28, 38 may be any pair of lines extending vertically in Fig. 5, while the two lines 29, 39 may be any of the pairs of lines extending horizontally in Fig. 5. The lines are terminate in spirals, such that the spiral ends of lines 28 and 29 are interleaved (though not touching), as are the spiral ends of lines 38 and 39.

Fig. 7(a) is a side view of a key 16, while Fig. 7(b) is a view of the underside of the key. The lower surface of the key includes a two semi-circular conductive portions 113, 213 respectively arranged over the spiral ends of the lines 28, 29 and 38, 39, and spaced apart by a notch 100. Thus, when the key 16 is depressed, the lines 28, 29, 38, 39 are electrically connected in pairs, i.e. lines 28 and 29 are electrically connected and lines 38, 39 are electrically connected.

The scan cycles used in the embodiment include a number of scan steps, in each of which one of the six pairs of vertical lines in Fig. 5 is fixed at a driving voltage, and, whenever any pair of vertical lines is fixed at the driving voltage, the voltages on the pairs of horizontal lines with which this pair of vertical lines intersects are monitored. For example, when lines 0, 1 are driven, all four other lines are monitored. When lines 1 , 3 are driven, only lines 4, 5 are monitored.

The keys 16 shown in Fig. 5 are used in combination with the keys 6 of Fig. 1 , to give an extended keypad. Furthermore, the keypad may include an additional key 116 shown in Fig. 8, which when operated connects all six of the lines pairwise, e.g. line 0 to line 3, line 1 to line 4 and line 2 to line 5.

Fig. 9 shows the flow diagram of the embodiment. The flow diagram of Fig. 9 is very similar to Fig. 4, so corresponding steps of Fig. 9 are given reference numbers which are higher by 100. In each step 117 the voltages are fixed of one of the vertical lines of Fig. 1 , or one of the pairs of vertical lines on Fig. 5, or the three vertical lines in Figs. 8 are fixed at the driving voltages (e.g. voltage low). In the case of a key of Fig. 1 , this is a single line labelled z. In the case of a key of Fig. 5, this is a two lines y and z. In the case of the key of Fig. 8, this is a set of three lines x, y, z. In each case z is the line corresponding to the pin of highest number.

According to which of these possibilities is presently in effect, the voltages on the corresponding horizontal lines which intersect with these vertical line(s), in other words lines z+1 , z+2, ....n, are initially set to a preparation voltage (e.g. voltage high) and then monitored, in step 118.

In step 119 it is determined whether the monitored voltage(s) indicate that one of the keys is pressed. If the result is positive, then the method proceeds to step 120 in which it is determined which key, when pressed, would given this measurement. Subsequently, in step 121 it is determined whether, on the previous scan cycle, the fact that this key was being pressed was registered. If not (i.e. if this is the first scan cycle in which it has been noted that this key is being pressed), then in step 122 this fact is registered. Alternatively, if the determination in step 121 is positive (i.e. the fact that the key is pressed has been noted in the previous scan cycle also), the method proceeds to step 123 in which the key press it confirmed. Following either of steps 122 or 123 (or if the result in step 119 was negative), the method proceeds to step 24 in which the value of x and/or y and/or z is changed. After step 24, the method returns to step 17. Therefore the method is repeated continuously, scanning though all possible values of x, y and z (in any order).

Whenever a positive confirmation is achieved in step 23, a confirmation signal is generated which triggers a separate process not shown in Fig. 9 in which the integrated circuit reacts to the confirmed key depression. For example an interrupt signal can be generated to a microprocessor which takes appropriate actions. Comparing what confirmation signals are generated in successive scan cycles allows the integrated circuit to detect new key depressions, and when keys are released.

Thus, the present embodiment makes it possible to increase the number of keys to ⁶C₂ plus ⁶C₄ plus ⁶C₆, that is 15+15+1.

Note that, from one perspective, the embodiment makes it possible to increase the number of keys, but at the cost that the method may erroneously interpret the simultaneous operation of two keys 6 as the operation of one of the keys 16. This occurs if the respective pairs of lines connected by the keys 6 are the same pairs of lines connected by the operation of the single key 16.

Although only a single embodiment of the invention has been described in detail, many variations of the invention are possible. For example, n can be chosen to be a higher integer, which is not necessarily even. In this case, the total number of keys possible by straightforward variations of the embodiment described in detail above, is ⁿC₂+ⁿC₄+...+ⁿC_m, where m=n if n is even, and otherwise m=n-1. For example, in the case that n equals 9, the total number of keys is ⁹C₂+⁹C₄+⁹C₆+⁹C₈=36+ 126+84+9=255 keys. This means that the number of keys possible in this embodiment, as compared to the analogue of Fig. 1 , is increased by 219 keys. Furthermore, as mentioned above, many other variations of the method are possible, as will be clear to one skilled in this art. In particular, it is not essential that the number of lines per key is even (although this is preferred).

Furthermore, as also mentioned above, it is not essential that for any group of lines there is exactly one key, as in Figs 1 , 5 and 8. Instead, each of the keys 16, 116 may in principle by replaced by a plurality of keys which each connect the same set of lines, but in different respective pairwise combinations. However, such keys require multiple scan steps to be distinguished, so this option is not preferred.

Claims

1. A data input apparatus including:

an integrated circuit having pins electrically connected to respective conductive lines, and a control logic for performing a series of scan steps in each of which the voltages of one or more of the pins are fixed and the voltages of the other pins are measured; and

a keypad including a plurality of keys, each key being arranged when operated to connect a plurality of the lines to each other;

wherein the keypad includes at least one key which is arranged when operated to form electrical connections among at least three of the lines.

2. A data input apparatus according to claim 1 in which the at least one key when operated forms connections between an even number of lines, and electrically connects those lines in pairs.

3. A data input apparatus according to claim 2 in which the at least one key when operated forms two pairwise connections between four lines.

4. A data input apparatus according to claim 2 or claim 3 in which the keypad includes one or more keys which when operated connect six lines to each other in three pairs.

5. A data input apparatus according to any preceding claim in which the keypad further includes one or more keys which when operated each connect exactly one pair of lines to each other.

6. A keypad including a plurality of lines and a plurality of keys which can be operated to electrically connect pairs of the lines to each other, at least one of keys being arranged when operated to form electrical connections among at least three lines.

7. A keypad according to claim 6 arranged when operated to electrically connect an even number of lines to each other pairwise.

8. A keypad according to claim 7 in which the keypad only includes keys which connect an even number of lines to each other pairwise.

9. A keypad according to claim 7 or 8, in which each key which is arranged to electrically connect to lines together pairwise includes, for each of the pairs of lines, a respective conductive element which, when the key is operated, is in electrical contact with both of the corresponding pair of lines.

10. A keypad according to any preceding claim in which, denoting the number of lines as n, there is a respective key for each of the ⁿC₄ possible ways in which two pairs of leads can be selected from among the n leads, and each of those ⁿC₄ keys is arranged, when operated, to electrically connect the corresponding two pairs of leads.

11. A keypad according to claim 10 in which the total number of keys is ⁿC₂+ⁿC₄+...+ⁿC_m, where m=n if n is even and otherwise m=n .

12. A method of registering the operations a user performs on a keypad including a matrix of conductive lines and a plurality of keys, each key being arranged when operated to connect a plurality of the lines to each other, and the keypad including at least one key which is arranged when operated to form electrical connections among at least three of the lines, the method including performing a series of scan steps in which the voltages of one or more of the lines are fixed and the voltages of other of the lines are measured.

13. A method according to claim 12 in which the keyboard includes one or more keys which when operated connect two or more pairs of lines pairwise, and the scan steps include scan steps in which it is determined any of such keys have been operated by fixing the voltages of one line of each pair and measuring the voltages of the other lines of each pair.

14. A method according to claim 12 or claim 13 in which, upon detection that a key has been operated, a confirmation step is performed.