Patent Description:
In some examples, useful for understanding the invention but not necessarily encompassed by the wording of the claims, a touch device includes a controller and a touch interface that includes a plurality of electrodes (e.g., sensors) and a driven shield. The controller is coupled to each of the plurality of electrodes and is configured to detect capacitance changes over time. The driven shield surrounds the plurality of electrodes in a plane such that the driven shield is located between each of the plurality of electrodes and each other of the plurality of electrodes. The driven shield and the plurality of electrodes are configured to be driven to a common voltage (e.g., a reference voltage).

In mutual mode implementations, the controller is coupled to the driven shield and to each of the plurality of electrodes. The driven shield is configured to function as a mutual mode transmitter for each of the plurality of electrodes, which operate as mutual mode receivers. Using the driven shield as the transmitter for each of the receivers reduces a number of input/output connections between the touch interface and the controller as compared to implementations in which each of the receivers has a corresponding unique transmitter.

In both mutual mode and self mode implementations, the driven shield may reduce cross coupling effects amongst the plurality of electrodes. Reduced cross coupling may cause capacitance differences between touched and untouched electrodes to be greater. Accordingly, the controller may use a higher threshold to determine whether a touch has occurred as compared to implementations that lack a driven shield. Such a higher threshold may reduce false positive touch detections caused by the presence of liquid. Further, because the driven shield is not kept at ground, liquid may be prevented from coupling the plurality of electrodes to ground and causing capacitance changes. Accordingly, the driven shield may increase reliability of a touch device in the presence of liquid.

The controller is configured to monitor capacitance changes in capacitance associated with the plurality of electrodes and detect touches accordingly.

In some examples, useful for understanding the invention but not necessarily encompassed by the wording of the claims, the controller is configured to set a touch detection threshold based on whether liquid is detected on the touch interface. By using an elevated threshold in response to detecting liquid on the touch interface, the controller may prevent false positives caused by water flowing across the touch interface.

In some examples, useful for understanding the invention but not necessarily encompassed by the wording of the claims, the controller is configured to select an electrode as a detected touched electrode in response to determining that a change in capacitance associated with the electrode is greater than detected changes in capacitance associated with other electrodes of the touch interface. Selecting the electrode associated with the greatest detected change in capacitance may reduce the likelihood of the controller selecting an electrode associated with a capacitance change caused by water flowing across the touch interface. For example, water flowing across the touch interface may couple a user's finger to one or more electrodes but an electrode closest to a user's finger may be associated with a greater capacitance change compared to other electrodes of the touch interface. Accordingly, selecting the electrode associated with the greatest detected change may improve accuracy of touch detection.

In some examples, useful for understanding the invention but not necessarily encompassed by the wording of the claims, the controller is configured to, in response to detection of a touch corresponding to a one of the electrodes, lock the touch interface. For example, the controller may lock detection to "<NUM>" in response to detecting a touch corresponding to an electrode associated with a "<NUM>" key. While the controller is locked to the particular value, the controller ignores capacitance changes indicating touches corresponding to other ones of the plurality of electrodes. For example, while the touch interface is locked, the controller may not output "<NUM>" despite detecting capacitance changes corresponding to an electrode associated with a "<NUM>" key. The controller maintains the lock until the controller detects a capacitance change indicating that the one of the plurality of electrodes is no longer touched. Locking the touch interface may prevent the controller from falsely reporting touches corresponding to other ones of the plurality of electrodes while a user touches the particular one of the plurality of electrodes and water dynamically flows across the touch device establishing electrical connections between the user and other ones of the plurality of electrodes.

An apparatus, a method and a computer readable storage device according to the invention are defined in the appended independent claims.

Capacitive touch devices and methods that may be more resilient to the presence of liquids are described. Referring to <FIG>, a block diagram of a touch detection system <NUM> is shown. The touch detection system <NUM> includes a touch interface <NUM> coupled to a controller <NUM>. The touch interface <NUM> includes a plurality of electrodes <NUM> and a driven shield <NUM>. The driven shield <NUM> may include an electrode. In some implementations, the plurality of electrodes and the driven shield <NUM> correspond to traces or pads on a printed circuit board (PCB). The controller <NUM> may be included on the same PCB as the touch interface <NUM>. In the illustrated example, the touch interface <NUM> further includes an overlay <NUM>. The overlay <NUM> may correspond to a layer located adjacent to the plurality of electrodes <NUM> and the driven shield <NUM>. The overlay <NUM> may include plastic or another material and may include touch buttons corresponding to the plurality of electrodes <NUM>.

The controller <NUM> corresponds to a microcontroller or other processing device configured to perform operations described herein. The controller <NUM> is configured to drive the driven shield <NUM> to a reference voltage and to charge the plurality of electrodes <NUM>. The controller <NUM> may further drive the plurality of electrodes <NUM> to the reference voltage. In mutual mode examples, the driven shield <NUM> acts as a transmitter while the plurality of electrodes <NUM> acts as receivers, and mutual capacitive couplings are created between the driven shield <NUM> and the plurality of electrodes <NUM>. Thus, in mutual mode examples, each of the plurality of electrodes <NUM> forms a capacitance sensor with the driven shield <NUM>. In self-mode examples, each of the plurality of electrodes <NUM> corresponds to a capacitance sensor.

The controller <NUM> is configured to detect changes in capacitance values associated with the plurality of electrodes <NUM>. In mutual mode examples, a capacitance value associated with an electrode corresponds to a mutual capacitance between that electrode and the driven shield <NUM>. In self mode examples, the capacitance value associated with the electrode corresponds to a capacitance of the electrode. In an illustrative example, the controller <NUM> is configured to detect a capacitance change associated with one of the plurality of electrodes <NUM> by counting a number of charge cycles the electrode uses to charge a reference capacitor to a reference capacitance.

In operation of mutual mode examples, the controller <NUM> monitors changes in capacitance values of mutual capacitance couplings between the plurality of electrodes <NUM> and the driven shield <NUM> and detects touches based on a comparison of detected changes to a threshold. For example, the controller <NUM> may determine that a user has touched one of the touch buttons of the overlay <NUM> based on a capacitance change in mutual capacitance between the driven shield <NUM> and one of the plurality of electrodes <NUM> corresponding to the button. The change in mutual capacitance may correspond to a change in mutual capacitance between the electrode and the driven shield <NUM> (e.g., in mutual mode examples) between a charge phase and a transfer phase. In mutual mode examples, the controller <NUM> may detect a touch in response to detecting a decrease in mutual capacitance that satisfies the threshold. In operation of self mode examples, the controller <NUM> monitors changes in capacitance values of the plurality of electrodes <NUM> and detects touches based on a comparison of detected changes to a threshold. For example, the controller <NUM> may determine that a user has touched one of the touch buttons of the overlay <NUM> based on a capacitance change in a corresponding one of the plurality of electrodes <NUM>. In self-mode examples, the controller <NUM> may detect a touch in response to detecting an increase in capacitance that satisfies the threshold. The arrangement of the driven shield <NUM> may reduce an occurrence of incorrect touch detections generated by the controller <NUM> (in both mutual mode and self mode examples) when liquid is present on a surface of the touch interface <NUM> as described further below.

Referring to <FIG>, a diagram of an example touch device <NUM> that includes the touch detection system <NUM> is shown. In the illustrated example, the overlay <NUM> corresponds to a touch surface embedded in a case <NUM>. The case <NUM> may include plastic or another material. The touch surface includes twelve touch buttons, including a first button <NUM> and a second button <NUM>. In some implementations, the touch device <NUM> is configured to control an electronic lock system. For example, the controller <NUM> may be configured to engage and disengage an electronic lock based on touches detected on the touch interface <NUM>. Alternatively, the controller <NUM> may be configured to signal a separate electronic lock controller based on touches detected on the touch interface <NUM>. In some examples, the overlay <NUM> may include a different number of touch buttons than depicted or may correspond to a touch screen.

<FIG> illustrates a first cross sectional view of the touch device <NUM> showing the driven shield <NUM> and the plurality of electrodes <NUM>. Each of the plurality of electrodes <NUM> corresponds to one of the plurality of buttons (e.g., mutual mode or self mode capacitance buttons) of the overlay <NUM>. For example, a first electrode 106a corresponds to the first button <NUM> and a second electrode 106b corresponds to the second button <NUM>. In a plane illustrated in <FIG>, the driven shield <NUM> surrounds the each of the plurality of electrodes <NUM> and is located between each of the plurality of electrodes <NUM> and each other of the plurality of electrodes <NUM>. For example, the driven shield <NUM> surrounds the first electrode 106a and the second electrode 106b and is located between the first electrode 106a and the second electrode 106b. As described above, the controller <NUM> is configured to drive the driven shield <NUM> to a reference voltage and to charge the plurality of electrodes <NUM>. The controller <NUM> may further drive the plurality of electrodes <NUM> to the reference voltage. Accordingly, signals that drive the plurality of electrodes <NUM> and the driven shield <NUM> may have similar or the same waveforms. Because the driven shield <NUM> is located between each of the plurality of electrodes <NUM> and each other of the plurality of electrodes <NUM>, the electric field generated by the driven shield <NUM> may reduce cross coupling of the plurality of electrodes <NUM>.

Cross coupling may occur through the air or through liquid present on the overlay <NUM>. For example, liquid flowing on a surface of the overlay <NUM> between the first button <NUM> and the second button <NUM> may electrically couple the first electrode 106a and the second electrode 106b. Cross coupling between the first electrode 106a may cause factors that affect a capacitance associated with the first electrode 106a (e.g., a touch) to also affect capacitance associated with the second electrode 106b. The electric field generated by the driven shield <NUM> may reduce cross coupling between the first electrode 106a and the second electrode 106b even when liquid is flowing between the first button <NUM> and the second button <NUM>. Reducing cross coupling between the first electrode 106a and the second electrode 106b may increase a difference in capacitance changes associated with the two electrodes 106a, 106b resulting from a user's finger touching the first button <NUM>. Therefore, the controller <NUM> may more easily discern that the touch corresponds to the first button <NUM> rather than the second button <NUM> as compared to systems that lack a driven shield.

Further, the placement of the driven shield <NUM> may prevent liquid from coupling the plurality of electrodes <NUM> with ground (or a voltage different from a voltage of the plurality of electrodes <NUM>). To illustrate, examples of touch interfaces may include a grounded element surrounding the first electrode 106a. In such examples, liquid present on the touch interface may couple an electrode with the grounded element resulting in a change in capacitance associated with the electrode. This may cause a touch associated with the electrode to be detected even when no finger is present on the touch interface. In contrast, liquid flowing from the first button <NUM> to another portion of the overlay <NUM> may not couple the first electrode 106a to ground because the driven shield <NUM> and the first electrode 106a are driven to the same reference voltage. Thus, the driven shield <NUM> may further reduce a chance that the controller <NUM> falsely detects a touch has occurred as a result of liquid present on the touch interface <NUM>.

In mutual mode examples, the controller <NUM> is configured to operate each of the electrodes of the plurality of electrodes <NUM> as mutual mode receivers and to drive the driven shield <NUM> as a mutual mode transmitter for each of the plurality of electrodes <NUM>. In an illustrative example, the controller <NUM> drives the plurality of electrodes <NUM> and the driven shield <NUM> to establish a first mutual capacitive coupling between the first electrode 106a and the driven shield <NUM> and a second mutual capacitive coupling between the second electrode 106b and the driven shield <NUM>. The controller is configured to monitor a first capacitance value of the first mutual capacitive coupling and a second capacitance value of the second mutual capacitive coupling to determine whether one of the first button <NUM> or the second button <NUM> has been touched. In some implementations, each of the electrodes <NUM> has a corresponding discrete connection to the controller <NUM>. Accordingly, the controller <NUM> may more accurately detect touches in the presence of liquid as compared to systems in which a controller receives a multiplexed signal from a group of transmitters. Because the driven shield <NUM> is used as a transmitter for both the first electrode 106a and the second electrode 106b, there may be fewer connections to the controller <NUM> from transmitters as compared to mutual mode touch sensor systems that use a unique transmitter for each receiver. Accordingly, the controller <NUM> may include fewer input/output pins dedicated to transmitters as compared to controllers used in other systems.

In addition, liquid located on the touch interface <NUM> may increase electric field coupling between one of the electrodes <NUM> and the driven shield <NUM> (e.g., because liquid has a higher dielectric constant than air). Accordingly, liquid present on the touch interface <NUM> may increase mutual capacitance between one of the electrodes <NUM> and the driven shield <NUM>. As described above, the controller <NUM> may detect touches based on decreases in mutual capacitance. Accordingly, the driven shield <NUM> may reduce false positives for at least this additional reason.

<FIG> illustrates a second cross sectional view of the touch device <NUM>. In the illustrated example, the plurality of electrodes <NUM> and the driven shield <NUM> correspond to traces or pads of a PCB <NUM>. The plurality of electrodes <NUM> and the driven shield <NUM> are embedded in a PCB core layer <NUM> which is adjacent to a ground layer <NUM>. The PCB core layer <NUM> may include a composite material such as an FR-<NUM> material. The ground layer <NUM> may include copper foil coupled to a ground point. While not illustrated, the controller <NUM> may be located on the PCB <NUM> as well. As illustrated, the driven shield <NUM> is located between the plurality of electrodes <NUM>. For example, the driven shield <NUM> is located between the first electrode 106a and the second electrode 106b. Accordingly, the electric field of the driven shield <NUM> may reduce cross coupling effects caused by liquid flowing across the overlay <NUM>. Further, the driven shield <NUM> may prevent liquid from coupling one of the plurality of electrodes <NUM> to ground.

Referring to <FIG>, a method <NUM> of detecting a touch in a capacitive touch system is illustrated. The method <NUM> may be performed by the controller <NUM> or by another controller in a capacitive touch system. While performing the method <NUM> the controller <NUM> or other controller periodically assesses capacitance values (e.g., changes in capacitance) associated with a plurality of elements (e.g., the plurality of electrodes <NUM>). The method <NUM> includes determining whether liquid is present on a touch interface, at <NUM>. For example, the controller <NUM> may determine whether liquid is present on the overlay <NUM>. The controller <NUM> may determine that liquid is present on the overlay <NUM> in response to detecting concurrent touches of two or more of the buttons of the overlay <NUM> within a threshold period of time. For example, the controller <NUM> may determine that liquid is present on the overlay <NUM> in response to determining that the controller <NUM> detected a touch to both the first button <NUM> and the second button <NUM> at the same time within the last <NUM> minutes.

In response to determining that no liquid is present on the touch interface, the method <NUM> includes setting a touch threshold to a base level, at <NUM>. In response to determining that liquid is present on the touch interface, the method <NUM> includes setting the touch threshold to an elevated level, at <NUM>. The touch threshold corresponds to a capacitance change used by the capacitive touch system to determine whether a touch has occurred. For example, the controller <NUM> may set a touch threshold to <NUM> picofarad (pF) in response to determining that no liquid is present on the overlay <NUM>. Alternatively, the controller <NUM> may set the touch threshold to <NUM> pF in response to determining that liquid is present on the overlay.

The method <NUM> further includes determining whether a change in capacitance associated with an electrode exceeds the touch threshold, at <NUM>. For example, the controller <NUM> may determine whether a capacitance associated with any of plurality of electrodes <NUM> has changed by an amount that satisfies the touch threshold. In mutual mode examples, the capacitances associated with the plurality of electrodes <NUM> correspond to mutual capacitances between each of the plurality of electrodes <NUM> and the driven shield <NUM>. Because the controller <NUM> uses an elevated touch threshold in response to determining that liquid is present on the overlay <NUM>, a touch to a wet area of the overlay <NUM> outside of the plurality of buttons may be less likely to cause a capacitance change associated with one of the plurality of electrodes <NUM> that satisfies the touch threshold. Accordingly, false positives may be prevented. If no capacitance change associated with the monitored elements exceeds the touch threshold, the method <NUM> includes continuing to monitor the capacitance changes and revaluating the touch threshold, at <NUM>.

The method <NUM> further includes setting a detected touched element to an element that is associated with a greatest change in capacitance among a plurality of monitored elements, at <NUM>. For example, the controller <NUM> may set a detected touched electrode to an electrode of the plurality of electrodes <NUM> that is associated with a greatest change in capacitance among the plurality of electrodes <NUM>. To illustrate, the controller <NUM> may set the detected touch electrode to the first electrode 106a in response to determining that the first electrode 106a is associated with a detected capacitance change greater than detected capacitance changes associated with the other electrodes in the plurality of electrodes <NUM>. Because the controller <NUM> selects the electrode that is associated with a highest capacitance change among the plurality of electrodes <NUM> as the detected electrode, the controller <NUM> may avoid selecting an electrode that is associated with a capacitance change caused by liquid coupling a user's finger to the electrode.

The method <NUM> further includes outputting a value based on the detected touched element, at <NUM>. For example, in response to determining that the first electrode 106a is the touched element, the controller <NUM> may output a value corresponding to the first button <NUM> associated with the first electrode 106a (e.g., "<NUM>"). In some implementations, the controller <NUM> may output the value to an electronic lock controller.

The method <NUM> further includes locking the touch interface, at <NUM>, and determining whether detected capacitance values indicate that the detected touched element has been released, at <NUM>. In response to determining that the detected touched element has not been released, the method <NUM> maintains the lock of the touch interface, at <NUM>. In response to determining that the detected touched element has been released, the method <NUM> includes unlocking the touch interface, at <NUM>, and continuing to monitor for detected touches. Thus, the method <NUM> may include disregarding capacitance values indicating detected touches to other elements until a determination that the detected touched element has been released. For example, after outputting a value corresponding to the first button <NUM> associated with the first electrode 106a, the controller <NUM> may lock the touch interface <NUM> until a determination that the first electrode 106a (or the first button <NUM>) has been released. The controller <NUM> may not generate touch output in response to locking of the touch interface <NUM>. Accordingly, the controller <NUM> may disregard (e.g., not generate output in response to) a detected touch associated with the second electrode 106b (or the second button <NUM>) while the touch interface <NUM> is locked. Accordingly, the controller <NUM> may be prevented from outputting erroneous touch detection output as water flows across the overlay <NUM> altering capacitances of the plurality of electrodes <NUM>. In response to detecting that the first electrode 106a (or the first button <NUM>) has been released, the controller <NUM> may resume detecting touches.

Thus, the method <NUM> may reduce erroneous touch detection output by increasing a touch detection threshold in response to a presence of liquid, by identifying a touched element by determining which of a plurality of elements is associated with a greatest change in capacitance, and by locking touch detection output until a touched element is released. Accordingly, the method <NUM> may be used to improve accuracy of touch detection systems that are deployed outdoors where weather lead to exposure to liquid.

Referring to <FIG> a block diagram of a computer system <NUM> that may detect touches according to the techniques described herein. The computer system <NUM> includes a computing device <NUM> and a touch interface <NUM>. The computing device <NUM> may correspond to the controller <NUM> and may be included in a touch device, such as the touch device <NUM>. The computing device <NUM> includes one or more processors <NUM> and one or more computer readable storage devices <NUM>. The one or more processors <NUM> may include one or more CPUs, one or more GPUs, one or more other processors, or a combination thereof. The one or more computer readable storage devices <NUM> may include one or more read only memory (ROM) devices, one or more random access memory (RAM) devices, one or more disc drive devices, one or more other types of memory devices, or a combination thereof. The one or more computer readable storage devices <NUM> store touch detection instructions <NUM> that are executable by the one or more processors <NUM> to perform one or more of the functions described herein. For example, the touch detection instructions <NUM> may be executable by the one or more processors <NUM> to perform operations described herein with respect to <FIG>, the method <NUM>, or a combination thereof. In particular, the touch detection instructions <NUM> may be executable by the one or more processors <NUM> to detect touches of the touch interface <NUM> according to the techniques and methods described herein. The touch interface <NUM> includes one or more capacitive touch elements (e.g., electrodes) and, in some examples, includes a driven shield, such as the driven shield <NUM>.

In this description, the term "couple" or "couples" means either an indirect or direct wired or wireless connection. Thus, if a first device couples to a second device, that connection may be through a direct connection or through an indirect connection via other devices and connections. The recitation "based on" means "based at least in part on. " Therefore, if X is based on Y, X may be a function of Y and any number of other factors.

Claim 1:
An apparatus, comprising:
a touch interface (<NUM>) comprising:
a plurality of electrodes (<NUM>); and
a shield device (<NUM>), which is configured to be driven to a common voltage and is configured to
establish a first mutual capacitive coupling with a first electrode of the plurality of electrodes (<NUM>); and
establish a second mutual capacitive coupling with a second electrode of the plurality of electrodes (<NUM>); and
a controller (<NUM>) coupled to the touch interface (<NUM>), the controller (<NUM>) configured to:
a) detect a touch based on a detected first capacitance value of the first mutual capacitive coupling and a detected second capacitance value of the second mutual capacitive coupling,
b) detect the touch in response to the detected first capacitance value, the detected second capacitance value, or a combination thereof satisfying a touch detection threshold;
characterised in that the controller is further configured to
c) increase the touch detection threshold in response to detecting liquid on the touch interface (<NUM>); and
d) determine that liquid is present on the touch interface (<NUM>) in response to determining that the detected first capacitance value and the second detected capacitance value indicate that multiple buttons of the touch interface (<NUM>) have been touched concurrently.