Designing a PCB with Atmel Touch Controls in Altium Designer

Facilitating the use of touch sensor technologies in your board designs, 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:

• Button (or key) sensor (single channel)
• Small spatially-interpolated slider sensor (3 channels)
• Small spatially-interpolated wheel sensor (3 channels)
• Medium spatially-interpolated slider sensor (3 channels)
• Medium spatially-interpolated wheel sensor (3 channels)
• Medium resistively-interpolated wheel sensor (12 channels, only 3 connected to the sensor controller).

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:

• Button (or key) sensor (single channel)
• 1-layer, small spatially-interpolated slider sensor (n-channels)
• 1-layer, small spatially-interpolated wheel sensor (n-channels)
• 2-layer, medium spatially-interpolated slider sensor (n-channels)
• 2-layer, medium/large spatially-interpolated wheel sensor (n-channels)
• 2-layer, medium resistively-interpolated wheel sensor (n-channels).

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.

Installing Atmel QTouch Touch Sensor Support

If support has not already been added during initial installation of the software, it can be added from the Configure Platform page, when managing the extensions and updates for your installation (click the  button, at the top-right of the main application window, then choose the Extensions and Updates entry from the associated menu):

1. From the Installed page of the view, simply click the Configure button at the top-right - to access the Configure Platform page.

2. Scroll to the bottom of the page and enable the entry for Atmel QTouch, in the Touch Sensor Support region of the page.

Then enable the Atmel QTouch option, under Touch Sensor Support.

3. Click the Apply button, back at the top-right of the page. Altium Designer must be restarted for the changes to take effect, so click Yes at the dialog prompt. The required files will be downloaded and installed, and Altium Designer restarted. Verify through Windows Explorer that the Atmel QTouch.IntLib is now available - in the \Users\Public\Documents\Altium\AD<VersionNumber>\Library\QTouch folder (for a default installation).

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).

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.

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.

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 QTouchButton component

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 SmallQTouchSlider component

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 SmallQTouchWheel component

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 MediumQTouchSlider component

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 MediumQTouchWheel component

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 MediumResQTouchWheel component

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 QMatrixButton component

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 SmallQMatrixSlider component

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 SmallQMatrixWheel component

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 MediumQMatrixSlider component 

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 MediumLargeQMatrixWheel component

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 MediumResQMatrixWheel component

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 Design Content area of the Altium Website.

Browse QTouch and QMatrix Controller components on the Altium Website.

Components can be browsed directly on these pages. In addition, each page offers the following two options:

• Go To Vault - click this button to view the components through the browser-based interface.
• Download Library - click this button to download the components in a zipped integrated library file.

Further Information

For detailed information regarding touch sensor design, refer to Atmel's Touch Sensor Design Guide, available at www.atmel.com.