Coded data generation or conversion – Bodily actuated code generator – Including keyboard or keypad
Reexamination Certificate
1999-12-03
2003-01-07
Edwards, Jr., Timothy (Department: 2635)
Coded data generation or conversion
Bodily actuated code generator
Including keyboard or keypad
C341S034000, C200S512000
Reexamination Certificate
active
06504492
ABSTRACT:
TECHNOLOGICAL FIELD
The invention concerns generally the technology of generating an input signal to an electronic device in response to a manual operation of a user. Especially the invention concerns a structure that allows a device manufacturer to freely design the outlook of a keyboard or the like.
BACKGROUND OF THE INVENTION
Keyboards or -pads are conventionally used for converting a manual action of a human user to an input signal comprehensible to a digital signal processing device.
FIG. 1
illustrates a known rectangular keypad that consists of N×M keys; here N=4 and M=5. The arrangement comprises N conductive input rows 101 to 104 and M conductive output columns
105
to
109
where normally the rows and columns do not have a galvanic contact with each other. At each junction of a row and a column there is a key, comprising a conductive dome shown as a dotted circle and supported over the junction so that normally it does not contact the intersecting conductors. Pressing for example the key shown as
110
will cause the conductive dome to produce a galvanic contact between row
104
and column
109
. An input voltage distributor
111
energises each of the input rows in cyclical turns at a rate that is expected to exceed the rate of pressing the keys by the user. An output detector
112
detects the energisation caused in one of the output lines when the energisation of the corresponding input line coincides with a conductive dome coupling the input and output lines at one intersection. The logical encoding block
113
converts the observation of a keystroke to a bit sequence that unequivocally indicates, which key was pressed.
The drawbacks of the arrangement of
FIG. 1
comprise the relatively high power dissipation of the N parallel voltage buffers included in block
111
that arc required to maintain the continuous sequential energisation of the input rows, as well as the electromagnetic interference which the rapid cyclical energisation of the rows tends to cause to any nearby sensitive electronic devices.
From the European patent publication number EP 695 041, which is incorporated herein by reference, there is known a keypad arrangement according to
FIG. 2. A
supply voltage Vcc is provided to a positive voltage rail
201
through a resistor
202
. From the positive voltage rail there is a connection to each column of keys through a resistor
203
-
206
so that each of the resistors has a different value. Each row of keys is coupled to a ground rail
207
so that from each row there is a connection to a common connection point through a differently valued resistor
208
-
212
, and from the common connection point there is a connection to the ground rail through a resistor
213
. The positive voltage rail
201
is coupled to a first output port
214
. The circuit comprises also a PNP transistor
215
the emitter of which is coupled to the supply voltage Vcc, the base of which is coupled to the positive voltage rail
201
through a resistor
216
and the collector of which is coupled to the ground rail
207
through a resistor
217
. The collector of the PNP transistor
214
is also coupled to a second output port
218
.
The idea of the keypad according to
FIG. 2
is that when a certain key is pressed, a resistive current path is produced between the positive voltage rail and the ground rail. The resistance value of the current path is unambiguously associated to the depressed key, because all the column resistors
203
-
206
and row resistors
208
-
212
have different values. The variable resistance of the current path acts as a part of a voltage divider together with the resistor
202
, which in turn causes the positive voltage rail to assume a voltage value that is also unambiguously associated to the key which was pressed. An A/D converter (not shown) connected to the first output port converts the voltage value of the positive voltage rail into a digital word representing the depressed key. The circuit built around the PNP transistor will generate an interrupt signal that is readable from the second output port and indicates when a key is pressed.
The keypad of
FIG. 2
is much more advantageous than that of
FIG. 1
in numerous ways: for example, it causes much less electromagnetic interference and dissipates much less power during operation. However, there are still certain drawbacks. A manufacturer of electronic devices will often want to put a series of slightly different models on the market. In many cases it is most advantageous to keep the inner structures the same from one model to another to as large an extent as possible, and use visible design features to distinguish the models from each other. If the different models have differently located keys in the keypad, or a different number number of keys, the resistor networks and the the printed circuit board that acts as the support structure of the keypad must all be specific to each model. It would be very advantageous if the arrangement of keys could be variable without modifications to the inner structures of the keypad.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a keypad structure that allows for the location and number of keys to be varied without essential modifications to the inner structyres of the keypad. It is also an object of the invention to provide a keypad that is easily adapted to mass production. A further object of the invention is to provide a keypad with a simple and reliable structure.
The objects of the invention are achieved by building the keypad on top of certain essentially continuous conducting means for providing a very large number of unambiguously identifiable current paths as a response to depressions at various locations on the keypad.
The keypad according to the invention is characterised in that it comprises an arrangement of essentially continuous conducting means next to the depressable keys and
connection creating means associated with each depressable key for providing, as a response to the depression of a key, an electrical connection through said essentially continuous conducting means so that the electrical characteristics of the created electrical connection uniquely identify the location of the depressed key in relation to said essentially continuous conducting means.
The invention applies also to an electronic device with a keypad, an analogue to digital converter and some digital circuitry. It is characteristic to the electronic device that
the keypad comprises an arrangement of essentially continuous conducting means next to the depressable keys and connection creating means associated with each depressable key for providing, as a response to the depression of a key, an electrical connection through said essentially continuous conducting means so that the electrical characteristics of the created electrical connection uniquely identify the location of the depressed key in relation to said essentially continuous conducting means, and
the analogue to digital converter is arranged to identify the electrical characteristics of the created electrical connection and to provide digital information that uniquely identifies the depressed key to the digital circuitry.
According to the invention the keypad structure comprises, under the part(s) that consitutes the actual keys, an arrangement of essentially continuous conductive means over a certain area. The conductive means are arranged so that in an idle state (no keys being pressed) there are essentially no current paths through them. The depression of a key creates a temporary current path through the continuous conductive means at a certain location. The electrical characteristics associated with such a temporarily created current path are unique to (fiat location. By sensing the electrical characteristics of the created current path it is possible to identify the location where a key was depressed.
The essential difference between the invention and most prior art keypad structures is that the arrangement of essentially continuous conductive me
Edwards, Jr. Timothy
Nokia Mobile Phones Ltd.
Perman & Green LLP
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