Capacitive touch screen linux

Introduction

Touch screen under Embedded Linux requires a kernel module that receives the hardware signals and exports them as an input device to be read in user space by a library.

As an example, if you are using Boot to Qt image with Capacitive Touch Display 7″ Parallel, your setup will look like the following flowchart:

On the other hand, if you are using Ångström X11 image with Resistive Touch Display 7″ Parallel, your setup will look like the following flowchart:

In this article, touch screen calibration will be discussed applied to different libraries and its methods to correctly calibrate your touchscreen display.

Resistive Touch Screen

Touch screen calibration almost always implies calibrating a resistive touch, since the capacitive touch panels usually are calibrated by default. It means that this article is most useful if you have a resistive touch panel.

Read the following article to learn more about Resistive Touch Screen on our Embedded Linux BSPs.

Toradex Embedded Linux Offerings

BSP Layers and Reference Images for Yocto Project

Select your BSP version from the tabs below:

BSP 5 provides Weston/Wayland support, as described in the BSP Layers and Reference Images for Yocto Project Software. The Reference Multimedia Image comes with weston-touch-calibrator which can be used to calibrate the touch screen:

You may need to change the default Weston configuration to make it work, though. See how we have implemented the weston-touch-calibrator container on Touch Screen Calibration (Torizon) as an example implementation. For example, possibly you’ll have to update the weston.ini.

On BSP 3, some SoMs are supported with X11 and others with Weston/Wayland, as described in the page BSP Layers and Reference Images for Yocto Project Software. Since there is only a console image, it is up to you add a calibration program, or to tweak values as explained in the corresponding graphics framework documentation.

BSP 2.x automatically performs a calibration upon first boot and will continue to ask for calibration in every boot until it is successfully completed.

The calibration application can be found in /usr/bin/xinput_calibrator .

Torizon

Torizon uses Weston and Libinput. Toradex provides a container for touch screen calibration. For more details read Touch Screen Calibration (Torizon).

Input Libraries

Touch screen calibration concerning the input libraries is provided in this section.

libinput

libinput is a library to handle input devices in Wayland compositors and to provide a generic X.Org input driver. It provides device detection, device handling, input device event processing and abstraction so minimize the amount of custom input code compositors need to provide the common set of functionality that users expect.

Concerning Toradex offerings, Libinput is used by:

Calibration

For static configuration via udev, one can set the LIBINPUT_CALIBRATION_MATRIX udev property as a environment variable with the following udev rule:

You can use the following command line examples to create a file with the udev rule.

echo 'ENV="1 0 0 0 1 0"' > /etc/udev/rules.d/libinput.rules 

echo 'ENV="1 0 0 0 -1 1"' > /etc/udev/rules.d/libinput.rules 

echo 'ENV="-1 0 1 0 1 0"' > /etc/udev/rules.d/libinput.rules 

echo 'ENV="-1 0 1 0 -1 1"' > /etc/udev/rules.d/libinput.rules 

Further information on the LIBINPUT_CALIBRATION_MATRIX, please access the documentation.

Display Servers and Frameworks

Touch screen calibration concerning display servers (such as Xorg and Wayland) or standalone frameworks (such as Qt) is provided in this section.

Qt

The Qt framework supports different input methods. Regardless of this article’s information, please also consult the official Qt documentation.

The Qt for Device Creation demo image uses libinput, therefore please refer to the previous libinput section for touchscreen calibration information.

See also

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Touch Screen Calibration (Linux)

This page has not been fully updated to reflect the changes made in Toradex Linux BSP 6. Some information may still apply to Toradex Linux BSP 6 configurations. If you encounter issues, please Send Feedback.
If you are using version 5 LTS, please visit the 5 LTS version documentation.

Introduction​

Touch screen under Embedded Linux requires a kernel module that receives the hardware signals and exports them as an input device to be read in user space by a library. As an example, if you are using Boot to Qt image with Capacitive Touch Display 7″ Parallel, your setup will look like the following flowchart: On the other hand, if you are using Ångström X11 image with Resistive Touch Display 7″ Parallel, your setup will look like the following flowchart: In this article, touch screen calibration will be discussed applied to different libraries and its methods to correctly calibrate your touchscreen display.

Resistive Touch Screen​

Touch screen calibration almost always implies calibrating a resistive touch, since the capacitive touch panels usually are calibrated by default. It means that this article is most useful if you have a resistive touch panel. Read the following article to learn more about Resistive Touch Screen on our Embedded Linux BSPs.

Toradex Embedded Linux Offerings​

BSP Layers and Reference Images for Yocto Project​

BSP 5 provides Weston/Wayland support, as described in the BSP Layers and Reference Images for Yocto Project Software. The Reference Multimedia Image comes with weston-touch-calibrator which can be used to calibrate the touch screen:

You may need to change the default Weston configuration to make it work, though. See how we have implemented the weston-touch-calibrator container on Touch Screen Calibration (Torizon) as an example implementation. For example, possibly you’ll have to update the weston.ini.

Torizon​

Torizon uses Weston and Libinput. Toradex provides a container for touch screen calibration. For more details read Touch Screen Calibration (Torizon).

Input Libraries​

libinput​

libinput is a library to handle input devices in Wayland compositors and to provide a generic X.Org input driver. It provides device detection, device handling, input device event processing and abstraction so minimize the amount of custom input code compositors need to provide the common set of functionality that users expect.

Calibration

For static configuration via udev, one can set the LIBINPUT_CALIBRATION_MATRIX udev property as a environment variable with the following udev rule:

You can use the following command line examples to create a file with the udev rule.

echo 'ENV="1 0 0 0 1 0"' > /etc/udev/rules.d/libinput.rules 

echo 'ENV="1 0 0 0 -1 1"' > /etc/udev/rules.d/libinput.rules 

echo 'ENV="-1 0 1 0 1 0"' > /etc/udev/rules.d/libinput.rules 

echo 'ENV="-1 0 1 0 -1 1"' > /etc/udev/rules.d/libinput.rules 

Further information on the LIBINPUT_CALIBRATION_MATRIX, please access the documentation.

Display Servers and Frameworks​

Touch screen calibration concerning display servers (such as Xorg and Wayland) or standalone frameworks (such as Qt) is provided in this section.

Qt​

The Qt framework supports different input methods. Regardless of this article’s information, please also consult the official Qt documentation.

The Qt for Device Creation demo image uses libinput, therefore please refer to the previous libinput section for touchscreen calibration information.

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First Steps with Capacitive Touch Display 10.1 Inch LVDS

This article provides information on how to start working with the Capacitive Touch Display 10.1 Inch LVDS, which includes how to set up the hardware (wiring), install and configure the necessary drivers for a touch demo.

Getting Started​

What I need to order​

The Capacitive Touch Display 10.1 Inch LVDS can be ordered with many Toradex computer on modules and carrier boards. See the compatible products.

Where do I order​

Cable Connection​

This topic provides pin connection details regarding connecting the Capacitive Touch Display 10.1 Inch LVDS to the carrier boards. Connect both the LVDS cable and the flat ribbon cable for the touch controller to the display. Please refer to the below instructions for connecting the display to your specific carrier board.

Connections on Ixora​

Important! The LVDS connector is directly connected to the power input connector. For this reason, use only 12V (+/-10%) power supplies with the board. Otherwise, you can damage the LVDS display or observe a malfunction.

See the picture below for the direct connection from the display to the Ixora board. Make sure to connect the pin 1 side of both display and touch controller to the respective pin 1 of the carrier board.

Connection on Apalis Evaluation Board​

Important! The LVDS connector is directly connected to the power input connector. For this reason, use only 12V (+/-10%) power supplies with the board. Otherwise, you can damage the LVDS display or observe a malfunction.

Connect the LVDS connector of the Display into the LVDS Connector (X13) of the carrier board. For the touch interface, a Capacitive Touch Adapter is required. Connect the flat ribbon cable of the Touch to the Touch Adapter. Make sure to connect the pin 1 side of the touch controller to the respective pin 1 side of the adapter board. Then, connect the adapter into the Apalis Evaluation Board using wires, as indicated in the table below.

Capacitive Touch Adapter V1.0	Apalis Evaluation Board V1.0 / V1.1	Remarks
X1, Pin 1: I2C_SDA		X8, Pin 40; X9, Pin A40: MXM3_209 (I2C1_SDA)
X1, Pin 2: I2C_SCL		X8, Pin 39; X9, Pin A39: MXM3_211 (I2C1_SCL)
X1, Pin 3: GND		X2/X3/X4, Pin 11: GND
X1, Pin 4: TOUCH_INT#		X2, Pin 6; X3, Pin A6: MXM3_11 (GPIO5)
X1, Pin 5: TOUCH_RESET#		X2, Pin 5; X3, Pin A5: MXM3_13 (GPIO6)
X1, Pin 6: +3.3V		X2/X3/X4, Pin 1: 3.3V_SW	Optional

Connections on Iris Carrier Board​

Important! The LVDS connector is directly connected to the power input connector. For this reason, use only 12V (+/-10%) power supplies with the board. Otherwise, you can damage the LVDS display or observe a malfunction.

See the picture below for the direct connection from the display to the Iris Carrier Board. Make sure to connect the pin 1 side of both display and touch controller to the respective pin 1 of the carrier board.

Connections on Verdin Development Board​

A Verdin DSI to LVDS Adapter is required to use this display on Verdin boards. The Verdin DSI to LVDS Adapter features a touch connector compatible with the Capacitive Touch Display 10.1″ LVDS. Connect both the flat ribbon cable of the touch panel and the LVDS Cable into the adapter. See the indication on the silk mask in the adapter board indicating the correct side of the contacts for the Touch’s flat ribbon cable. Connect the adapter into the Verdin Development Board, as indicated in the figure below.

Connections on Dahlia Carrier Board​

A Verdin DSI to LVDS Adapter is required to use this display on Verdin boards. The Verdin DSI to LVDS Adapter features a touch connector compatible with the Capacitive Touch Display 10.1″ LVDS. Connect both the flat ribbon cable of the Touch and the LVDS Cable into the adapter. See the indication on the silk mask in the adapter board indicating the correct side of the contacts for the Touch’s flat ribbon cable. Connect the adapter into the Dahlia Board, as indicated in the figure below.

Installation on Embedded Linux​

TorizonCore 5​

On TorizonCore 5, Toradex deploys pre-compiled and ready-to-use device tree overlays for this display, inherited from the BSP layers. Enabling them for evaluation can be done with few commands. Learn how to do it on Setting up Displays with Torizon.

Reference Images for Yocto Project 5​

On BSP 5, Toradex deploys pre-compiled and ready-to-use device tree overlays for this display. This enables you to evaluate it with few commands and very fast. Learn how to do it on Device Tree Overlays (Linux).

For more advanced use cases, please refer to the article Display Output, Resolution and Timings (Linux).

Adjusting the Brightness​

Read the dedicated article Backlight (Linux).

Touch Screen​

Resistive touch screen works out-of-the-box in our BSP. To learn more about resistive touch, read the article Resistive Touch Screen (Linux).

Touch Screen Calibration​

Read the dedicated articles:

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