Support for Atmel Touch Controls

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Support for Atmel Touch Controls

Contents

How many of us got into electronics because we were drawn by the myriad of knobs, lights and other suitably gadget-centric controls? Fast forward a good few years and that allure is still there, only it is now replaced with the "Snazzy GUI" factor – electronic products that have a sleek, sexy interface. Central to these ever-advancing (and shrinking) product interfaces is touch control. Subtle yet powerful, a simple touch here or a slide there will execute an associated command, making the product not only more efficient to use, but also engaging and fun. Pick up your favorite mp3 player and you will soon realize that touch controls allow access to menus, control actions such as play, pause and stop, and let's not forget the wheel's effortless ability to dial-up the required volume!

To accommodate the use of such controls in your electronic products, Altium Designer provides support for creating planar capacitive sensor patterns on your PCB, for use with the range of Atmel®   QTouch® and QMatrix® sensor controllers.

Supported Self-Capacitance Type Sensors

The following self-capacitance type sensors are supported for use in your PCB designs:

A button (or key) sensor is a zero-dimensional sensor. It has a single point of contact. Slider and wheel sensors are one-dimensional sensors – they detect movement of your finger along a single axis.

A spatially-interpolated sensor uses the geometry of its electrodes to interpolate the electric fields. A resistively-interpolated sensor uses physical resistors to provide the interpolation.

Each channel (electrode) of these sensors has a single, direct connection to the sensor controller. Such sensors are non-directional, in terms of their emitted electric fields. Although they can be used with or without an overlying panel, electrostatic discharge (ESD) implications – for the associated controller device – is a major influence for such a panel being used.

All of these sensors are suited for use with Atmel QTouch sensor controllers.

Supported Mutual-Capacitance Type Sensors

The following mutual-capacitance type sensors are supported for use in your PCB designs:

A button (or key) sensor is a zero-dimensional sensor. It has a single point of contact. Slider and wheel sensors are one-dimensional sensors – they detect movement of your finger along a single axis.

A spatially-interpolated sensor uses the geometry of its electrodes to interpolate the electric fields. A resistively-interpolated sensor uses physical resistors to provide the interpolation.

Each of these sensors has X (transmit) and Y (receive) electrodes, with the mutual capacitance between X and Y measured by the sensor controller. For slider- and wheel-based sensors, multiple channels have unique X-electrode connections to the sensor controller, with a commoned Y-electrode connection. Such sensors should be used with an overlying panel, bonded with no air gaps. It is the panel that provides a suitable conduit for the electric fields between the X and Y electrodes.

All of these sensors are suited for use with Atmel QMatrix sensor controllers.

Sensor Implementation

A touch sensor is implemented in a design by placing and configuring the required sensor type from the dedicated Atmel QTouch integrated library (Atmel QTouch.IntLib), located in the \Library\QTouch folder of the installation.

The QTouch folder, and associated integrated library, will be present in the \Library folder, provided the Atmel QTouch plugin is installed as part of your Altium Designer installation. This plugin can be found on the PCB Design Tools page, when browsing plugins through the Plugins view.

When configured as required, simply update the target PCB – an ECO is used to effect the required changes, resulting in the creation of the sensor pattern for placement on the PCB. Each sensor component on the PCB isn't a footprint in the normal sense, but rather the actual copper electrode pattern. An overlaying panel would be placed over a sensor when the board is assembled.

Implementing a touch control is a snap - just place the required sensor type component on the schematic, configure it as applicable to your design needs, then push the changes over to the PCB to obtain the sensor pattern.

A sensor pattern can also be modified on the PCB side, and the changes pushed back to the relevant schematic sheet through an ECO.

The following sections take a closer look at the configurable sensor components available for placement in a design, their configuration options, and the resulting sensor pattern obtained on the PCB side. In each case, the default configurations are presented.

As with all configurable schematic components in Altium Designer, access to the associated configuration dialog for a sensor component is made by right-clicking over the component and choosing Configure from the context menu. Alternatively, click the Configure button from the associated properties dialog for the component.

QTouchButton

Use the QTouchButton component to implement a button (key) sensor. This is a self-capacitance, zero-dimensional sensor, with a single channel for connection directly to an Atmel QTouch sensor controller. The resulting sensor pattern on the PCB is a simple rectangular-shaped electrode.

Default configuration and resulting sensor pattern for the rectangular QTouch button.

SmallQTouchSlider

Use the SmallQTouchSlider component to implement a small-size slider sensor. This is a self-capacitance, 1-dimensional, spatially-interpolated sensor, with three channels for connection directly to an Atmel QTouch sensor controller. The resulting sensor pattern on the PCB is comprised of simple rectangular-shaped electrodes. The pattern consists of two full sized electrodes for channels 1 and 2, with channel 3 divided into two half-sized electrodes at either end.

Default configuration and resulting sensor pattern for the small QTouch slider.

SmallQTouchWheel

Use the SmallQTouchWheel component to implement a small-size wheel sensor. This is a self-capacitance, 1-dimensional, spatially-interpolated sensor, with three channels for connection directly to an Atmel QTouch sensor controller. The resulting sensor pattern on the PCB is comprised of simple wedge-shaped electrodes.

Default configuration and resulting sensor pattern for the small QTouch wheel.

MediumQTouchSlider

Use the MediumQTouchSlider component to implement a medium-size slider sensor. This is a self-capacitance, 1-dimensional, spatially-interpolated sensor, with three channels for connection directly to an Atmel QTouch sensor controller. The resulting sensor pattern on the PCB is comprised of toothed electrodes. The pattern consists of two full sized electrodes for channels 1 and 2, with channel 3 divided into two half-sized electrodes at either end.

Default configuration and resulting sensor pattern for the medium QTouch slider.

MediumQTouchWheel

Use the MediumQTouchWheel component to implement a medium-size wheel sensor. This is a self-capacitance, 1-dimensional, spatially-interpolated sensor, with three channels for connection directly to an Atmel QTouch sensor controller. The resulting sensor pattern on the PCB is comprised of toothed electrodes.

Default configuration and resulting sensor pattern for the medium QTouch wheel.

MediumResQTouchWheel

Use the MediumResQTouchWheel component to implement a medium-size wheel sensor. This is a self-capacitance, 1-dimensional, resistively-interpolated sensor, with three channels for connection directly to an Atmel QTouch sensor controller. The resulting sensor pattern on the PCB is comprised of wedge-shaped electrodes.

Default configuration and resulting sensor pattern for the medium resistively-interpolated QTouch wheel.

When configuring the sensor, you can choose how many electrode 'spacer segments' are used, equally, between channels. The default configuration uses 3 segments, resulting in 12 wedge-shaped X electrodes in the pattern. Remember that only 3 of these electrodes are connected back to the sensor controller. For this default configuration, the 3 channels connected to the sensor controller are associated with pins 1, 5 and 9 of the component.

To provide the electrically-driven interpolation of the sensors' electric fields, additional resistors must be used in the design, typically connecting a total of 100kOhms between successive channels that are connected to the controller (or 25kOhms between electrode segments). The following image shows an example of resistors wired to the sensor component to provide the required resistance levels, for the default component configuration.

Example of resistors connected to the sensor component to provide the electrical interpolation for the sensor.

QMatrixButton

Use the QMatrixButton component to implement a button (key) sensor. This is a mutual-capacitance, zero-dimensional sensor, with a single channel (one X and one Y electrode) for connection directly to an Atmel QMatrix sensor controller. The resulting sensor pattern on the PCB consists of interlocking fingers of the X and Y electrodes, in an overall rectangular shape. The Pattern for the X electrode completely surrounds that for the Y electrode.

Default configuration and resulting sensor pattern for the rectangular QMatrix button.

SmallQMatrixSlider

Use the SmallQMatrixSlider component to implement a small-size slider sensor. This is a mutual-capacitance, 1-dimensional, spatially-interpolated sensor, with multiple channels for connection directly to an Atmel QMatrix sensor controller. The resulting sensor pattern on the PCB resembles a 1xn array of buttons, where n is the number of channels defined. X and Y electrodes again are implemented as interlocking fingers. There is a gap between each successive X electrode. The Y electrode is continuous (it is common to all channels), with an additional finger in this gap. Isolated regions of the same X electrode are connected using vias and a track placed on the opposite layer of the board.

Default configuration and resulting sensor pattern for the small QMatrix slider.

SmallQMatrixWheel

Use the SmallQMatrixWheel component to implement a small-size wheel sensor. This is a mutual-capacitance, 1-dimensional, spatially-interpolated sensor, with multiple channels for connection directly to an Atmel QMatrix sensor controller. The resulting sensor pattern on the PCB resembles a 1xn circular array of buttons, where n is the number of channels defined. X and Y electrodes again are implemented as interlocking fingers, with tapering of the X-electrode fingers. There is a gap between each successive X electrode. The Y electrode is continuous (it is common to all channels), with an additional finger in this gap. Isolated regions of the same X electrode are connected using vias and a track placed on the opposite layer of the board.

Default configuration and resulting sensor pattern for the small QMatrix wheel.

MediumQMatrixSlider

Use the MediumQMatrixSlider component to implement a 2-layer medium-size slider sensor. This is a mutual-capacitance, 1-dimensional, spatially-interpolated sensor, with multiple channels for connection directly to an Atmel QMatrix sensor controller. The resulting sensor pattern on the PCB is composed of n slanting X electrodes, where n is the number of channels defined. There is a gap between each successive X electrode. The Y electrode is continuous (it is common to all channels) and consists of a number of horizontal 'fingers'. The Y electrode is located on the Top Layer, with the X electrodes located behind, on the Bottom Layer.

Each X electrode segment is 4mm in height. For a slider that is greater in height, additional segments are essentially stacked, in an alternating zig-zag fashion. An additional Y electrode finger is added for each level of segments in this stack. For the default configuration, where the height of the slider is 12mm, the stack incorporates three segments for each X electrode. The common Y electrode has three fingers.

Default configuration and resulting sensor pattern for the medium QMatrix slider.

MediumLargeQMatrixWheel

Use the MediumLargeQMatrixWheel component to implement a 2-layer medium-size wheel sensor. This is a mutual-capacitance, 1-dimensional, spatially-interpolated sensor, with multiple channels for connection directly to an Atmel QMatrix sensor controller. The resulting sensor pattern on the PCB is composed of n curved-tooth X electrodes, where n is the number of channels defined. There is a gap between each successive X electrode. The Y electrode is continuous (it is common to all channels) and consists of a number of 'rings'. The Y electrode is located on the Top Layer, with the X electrodes located behind, on the Bottom Layer.

Each X electrode segment is radially 4mm in height. For a wheel that is greater in diameter, additional segments are essentially stacked, radially outward, in an alternating curved-tooth fashion. An additional Y electrode 'ring' is added for each level of segments in this stack. For the default configuration, where the inner diameter is 16mm and outer diameter is 40mm, the stack incorporates three segments for each X electrode. The common Y electrode has three rings accordingly.

Default configuration and resulting sensor pattern for the medium/large QMatrix wheel.

MediumResQMatrixWheel

Use the MediumResQMatrixWheel component to implement a 2-layer medium-size wheel sensor. This is a mutual-capacitance, 1-dimensional, resistively-interpolated sensor, with multiple channels for connection directly to an Atmel QMatrix sensor controller. The resulting sensor pattern on the PCB is composed of n curved-tooth X electrodes, where n is the number of channels defined. There is a gap between each successive X electrode. The Y electrode is continuous (it is common to all channels) and consists of a number of 'rings'. The Y electrode is located on the Top Layer, with the X electrodes located behind, on the Bottom Layer.

Each X electrode segment is radially 4mm in height. For a wheel that is greater in diameter, additional segments are essentially stacked, radially outward, in an alternating curved-tooth fashion. An additional Y electrode 'ring' is added for each level of segments in this stack. For the default configuration, where the inner diameter is 7.5mm and outer diameter is 30mm, the stack incorporates three segments for each X electrode. The common Y electrode has three rings accordingly.

Default configuration and resulting sensor pattern for the medium resistively-interpolated QMatrix wheel.

When configuring the sensor, you can choose how many electrode 'spacer segments' are used, equally, between channels. The default configuration 4 channels and uses 3 spacer segments, resulting in 16 curved-tooth X electrodes in the pattern. For this default configuration, the 4 channels connected to the sensor controller are associated with pins 1, 5, 9 and 13 of the component.

To provide the electrically-driven interpolation of the sensors' electric fields, additional resistors must be used in the design, typically connecting a total of between 2kOhms and 100kOhms between the n channels that are connected to the controller. The following image shows an example of resistors wired to the sensor component to provide the required resistance levels, for the default component configuration.

Example of resistors connected to the sensor component to provide the electrical interpolation for the sensor.

Atmel Sensor Controllers

Atmel QTouch and QMatrix sensor controllers – to which the corresponding electrodes from the sensor patterns connect – can be found on the Atmel Touch Solutions page, within the Unified Components section of the Content Store. Browse components directly in the store or through the browser-based interface to the Altium Vault in which the components reside. Connect to the Altium Vault through Altium Designer and place components into your designs. Alternatively, download the associated integrated library (Atmel Touch Solutions.IntLib),as a Zip file, from the store page.

Further Information

For detailed information regarding touch sensor design, refer to Atmel's Touch Sensors Design Guide (doc10620.pdf), available at www.atmel.com.

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