Analysis and Common Solutions to LCD Image Sticking Issues

1. What is LCD Display Image Sticking

Image Sticking refers to the persistence of a static image on a display screen even after the content has changed. Image Sticking, Image Retention, Residual Image, and sometimes also referred to as screen aging phenomenon (Burn-In), are terms used to describe the effect of static images on subsequent image displays. This can involve the rapid disappearance of previous static content or temporary lingering of aged images.

Fig.1 Good Display
Fig.2 Image Sticking Display

2.The definitions and causes of Image Sticking Display

In TFT (Thin Film Transistor) displays, liquid crystal (LC) is a material with polar properties. An electric field can cause it to twist correspondingly.

In TFT (Thin Film Transistor) displays, liquid crystal (LC) must be driven by alternating current (AC). If direct current (DC) were used, it would disrupt the polarity of the crystals. In reality, there is no such thing as perfectly symmetrical alternating current. When continuously driving the pixels of a TFT, tiny inherent imbalances attract free ions to the internal electrodes. These ions adsorbed onto the internal electrodes create a drive effect similar to a combination of DC and AC.

In display fabrication, there are 3 main reasons which can cause image sticking.

(1) Insufficient alignment capability
PI (Polyimide) material is responsible for liquid crystal alignment. The liquid crystals in the white grid area rotate, while those in the black grid area do not. The rotation of liquid crystals is influenced by both the external electric field and intermolecular forces. The interaction force between the PI (polyimide) molecules on the surface of the liquid crystal is greater than the external electric field force, so the liquid crystal molecules on the surface do not rotate. The closer to the middle layer, the greater the effect of the external electric field on the liquid crystals, and the rotation angle approaches the theoretical value. During continuous signal output, the liquid crystals in the white grid area affect the surface liquid crystals through intermolecular forces (electrostatic force and dispersion force). If the alignment capability of the PI film is poor, the pre-tilt angle of the surface liquid crystals will change as the liquid crystals rotate. In Figure C, when switching to a grayscale image, because the pre-tilt angle of the liquid crystals in the white grid area has deviated from that of the black grid area, under the same grayscale voltage, the liquid crystals in the region where the angle deviation has occurred are more likely to rotate to the theoretical angle, resulting in an increase in transmittance and thus causing image sticking.

(2) Impurity of Liquid Crystal Material
Asymmetric alternating current (AC) driving occurs in the pixel area, and the part of the voltage that deviates from the center is the direct current (DC) bias. The DC bias attracts impurity ions within the screen, causing ion accumulation and resulting in residual DC bias. When switching display screens, due to the effect of residual DC bias, liquid crystal molecules influenced by ions fail to maintain the state required by the design, causing differences in brightness between areas with ion accumulation and other regions, leading to undesirable image sticking.

(3) Distortion of Driving Waveform
By applying different voltages, the rotation angle of liquid crystal molecules can be controlled to display different images. Here, the concepts of γ value and Vcom need to be introduced.
In simple terms, γ value divides the transition from white to black into 2 to the power of N (6 or 8) equal parts. γ voltage is used to control the gradation of the display, usually divided into G0 to G14. The first γ voltage and the last γ voltage represent the same gray level, but they correspond to positive and negative voltages respectively.
To prevent the formation of inertial deviation in liquid crystal molecules, dynamic voltage control is required. Vcom voltage is the reference voltage at the midpoint of G0 to G14. Specifically, Vcom is usually positioned between the first and last γ voltages. However, in practice, due to differences in peripheral circuits, adjusting the match between Vcom and γ voltages is necessary. When Vcom is adjusted to its optimum value, the positive and negative frame voltages of the pixels are symmetric, resulting in equal brightness for both positive and negative frames. However, when Vcom deviates from the center value, the voltage difference between positive and negative frames of the pixels is no longer the same, leading to a change in brightness between positive and negative frames.
When the Vcom voltage is set incorrectly, it can cause charged ions inside the liquid crystal to adsorb at the upper and lower ends of the glass, forming an inherent electric field. After switching the screen, these ions may not be immediately released, or the liquid crystal molecules may become disordered during state transitions, preventing the liquid crystal molecules from immediately rotating to the desired angle.

3.TFT LCD Image Sticking Testing

The following gives a fast-testing method:
Room temperature; Displaying a black and white checkerboard pattern (each square approximately 60×60 pixels); Static display for 30 minutes. Displaying full-screen 128 (50%) gray; after waiting for 10 seconds, no ghosting visible is deemed as qualified.
(Note: This is a destructive reliability test, not a routine test.)

In a TFT with normal white, the white areas receive the minimum driving voltage, while the black areas receive the maximum driving voltage. Free ions within the TFT are more likely to be attracted to the black areas (those with higher driving voltage). When displaying full-screen 128 (50%) gray, the entire screen will use the same driving voltage, causing ions to quickly leave their previously attracted positions. Additionally, when displaying full-screen 128 (50%) gray, anomalies in the display are more likely to be noticeable.

4. Common Methods to Resolve Image Sticking Issues

1) Screensaver: When the system is idle, the pixels of the TFT display different content, either displaying a moving screensaver or periodically switching content, to avoid displaying static images for more than 20 minutes.

2) If the image sticking occurs already, leaving the TFT powered off for several hours presents an opportunity for recovery; (recovery may take up to 48 hours in some cases). Or creating an all-white image and moving it across the screen for several hours without turning on the backlight. There are many image sticking repair software available online that may also be helpful. Once ghosting occurs, it becomes more likely to recur, so proactive measures are needed to prevent the reappearance of image sticking in TFT LCD displays.

3) Adjusting the Vcom voltage to match the γ voltage helps prevent ghosting caused by residual voltage in liquid crystal molecules.

4) Adjust discharge timing to ensure rapid release of residual voltage in liquid crystal molecules. In circuit design, specialized voltages are typically used to control the first and last γ voltages. Here, VGH and VGL represent G0 and G14, respectively. If the discharge of VGH and VGL is slow during system sleep, it can also result in an excessive residual voltage in the liquid crystal molecules. When the system wakes up, there is a chance of ghosting occurring.

5) Image sticking on LCD screens typically falls under the category of functional defects in LCD displays and requires LCD panel manufacturers to perform adjustments. Generally, reputable LCD display panel manufacturers by using high quality orientation alignment PI material and high purity liquid crystal material will reduce the possibility of image sticking.

• Firstly, it’s important to confirm whether the current settings of VSPR/VSNR meet the glass requirements.
• Verify the optimal VCOM value, which can be determined by measuring the flicker value using CA210. A smaller flicker value indicates a better VCOM value.
• Re-scan the gamma and observe whether ghosting persists.
• Asymmetric Gamma: Typically, tuning symmetric gamma, where the absolute values of positive and negative voltages for each gray level are equal. This approach relies on the LCD glass’s VT curve being symmetric. However, if the VT curve of the glass is asymmetric, asymmetric gamma adjustment is needed.
• VT curve: A curve representing the relationship between liquid crystal voltage and transmittance.
• Asymmetric gamma typically occurs in two scenarios: 1) Overall polarity offset: In this case, one polarity is shifted overall. Adjustments to VSPR/VSNR are required to address this state. 2) Single or multiple order offset: In this scenario, specific points on the gamma curve need voltage adjustments to address the offset.

TFT Display vs Super AMOLED, which is Better?

Thanks for the display technology development, we have a lot of display choices for our smartphones, media players, TVs, laptops, tablets, digital cameras, and other such gadgets. The most display technologies we hear are LCD, TFT, OLED, LED, QLED, QNED, MicroLED, Mini LED etc. The following, we will focus on two of the most popular display technologies in the market: TFT Displays and Super AMOLED Displays.

TFT Display

TFT means Thin-Film Transistor. TFT is the variant of Liquid Crystal Displays (LCDs). There are several types of TFT displays: TN (Twisted Nematic) based TFT display, IPS (In-Plane Switching) displays. As the former can’t compete with Super AMOLED in display quality, we will mainly focus on using IPS TFT displays.


OLED means Organic Light-Emitting Diode. There are also several types of OLED, PMOLED (Passive Matrix Organic Light-Emitting Diode) and AMOLED (Active Matrix Organic Light-Emitting Diode). It is the same reason that PMOLED can’t compete with IPS TFT displays. We pick the best in OLED displays: Super AMOLED to compete with the LCD best: IPS TFT Display.


Light Source it emits own light It requires a backlight
Thickness Very slim profile Thicker because of the backlight
Contrast Higher because of dark background Lower because of backlighting
Viewing Angles All around It has color changes at extreme viewing angles
Colors Bright and vibrant colors available Not the same good compared with AMOLED
Super dark color Easily available dark background Difficult because the backlight leakage
Super White Color Difficult to get because color mix difficult which can look yellowish Easily avaible by using white LED backlight
Sunlight Readable Needs to drive hard and difficult Easily and low cost to get by using high brightness backlight, transflective displays, optical bonding and surface treatment
Power Consumption Lower because of selective display area and better battery life Higher because of backlight on
Life time Shorter, especially affected by the presence of water Longer
Cost Very high Very competitive prices
Availability Limited sizes and manufacturers Widely available on different sizes and many manufacturers to choose from

If you have any questions about Orient Display displays and touch panels. Please feel free to contact: Sales Inquiries, Customer Service or Technical Support.

What is the difference between LED and LCD display?

Although there are big differences between LCD and LED displays, there are a lot of confusion in the market which shouldn’t happen. Part of the confusion comes from the manufacturers. We will clarify as below.

LCD Displays vs LED Displays

LCD stands for “liquid crystal display”. LCD can’t emit light itself; it has to use a backlight. In the old days, manufacturers used to use CCFL (cold cathode fluorescent lamps) as backlight, which is bulky and not environment friendly. Then, with the development of LED (light emitting diode ) technology, more and more backlights use LEDs. The manufacturers name them as LED monitors or TV which makes the consumers think they are buying LED displays. But technically, both LED and LCD TVs are liquid crystal displays. The basic technology is the same in that both television types have two layers of polarized glass through which the liquid crystals both block and pass light. So really, LED TVs are a subset of LCD TVs.

Quantum Dot Displays

Quantum-dot TVs are also widely discussed for recent years. It is basically a new type of LED-backlit LCD TV. The image is created just like it is on an LCD screen, but quantum-dot technology enhances the color.

For normal LCD displays, when you light up the display, all the LEDs light up even for unwanted area (for example, some areas need black). Whatever perfect the LCD display made, there is still small percentage of light transmitting through the LCD display which makes it difficult to make the super black background. The contrast decreases.
Quantum-dot TV can have full-array backlit quantum-dot sets with local-dimming technology (good for image uniformity and deeper blacks). There can be edge-lit quantum-dot sets with no local dimming (thinner, but you may see light banding and grayer blacks).

Photo-emissive quantum dot particles are used in RGB filters, replacing traditional colored photoresists with a QD layer. The quantum dots are excited by the blue light from the display panel to emit pure basic colors, which reduces light losses and color crosstalk in RGB filters, improving display brightness and color gamut. Although this technology is primarily used in LED-backlit LCDs, it is applicable to other display technologies which use color filters, such as blue/UV AMOLED(Active Matrix Organic Light Emitting Diodes)/QNED(Quantum nano-emitting diode)/Micro LED display panels. LED-backlit LCDs are the main application of quantum dots, where they are used to offer an alternative to very expensive OLED displays.

Micro LEDs and Mini LEDs

Micro LED is true LED display without hiding at the backside of the LCD display as backlight. It is an emerging flat-panel display technology. Micro LED displays consist of arrays of microscopic LEDs forming the individual pixel elements. When compared with widespread LCD technology, micro-LED displays offer better contrast, response times, and energy efficiency.

Micro LEDs can be used at small, low-energy devices such as AR glasses, VR headsets, smartwatches and smartphones. Micro LED offers greatly reduced energy requirements when compared to conventional LCD systems while has very high contrast ratio. The inorganic nature of micro-LEDs gives them a long lifetime of more than 100,000 hours.

As of 2020, micro LED displays have not been mass-produced, though Sony, Samsung and Konka sell microLED video walls and Luumii mass produces microLED lighting. LG, Tianma, PlayNitride, TCL/CSoT, Jasper Display, Jade Bird Display, Plessey Semiconductors Ltd, and Ostendo Technologies, Inc. have demonstrated prototypes. Sony and Freedeo already sells microLED displays as a replacement for conventional cinema screens. BOE, Epistar and Leyard have plans for microLED mass production. MicroLED can be made flexible and transparent, just like OLEDs.
There are some confusions between mini-LED used in LCD backlight as Quantum dot displays. To our understanding, mini-LED is just bigger size of micro LED which can be used for larger size of cinema screen, advertisement walls, high end home cinema etc. When discussing Mini-LED and Micro-LED, a very common feature to distinguish the two is the LED size. Both Mini-LED and Micro-LED are based on inorganic LEDs. As the names indicate, Mini-LEDs are considered as LEDs in the millimeter range while Micro-LEDs are in the micrometer range. However, in reality, the distinction is not so strict, and the definition may vary from person to person. But it is commonly accepted that micro-LEDs are under 100 µm size, and even under 50 µm, while mini-LEDs are much larger.

When applied in the display industry, size is just one factor when people are talking about Mini-LED and Micro-LED displays. Another feature is the LED thickness and substrate. Mini-LEDs usually have a large thickness of over 100 µm, largely due to the existence of LED substrates. While Micro-LEDs are usually substrate less and therefore the finished LEDs are extremely thin.
A third feature that is used to distinguish the two is the mass transfer techniques that are utilized to handle the LEDs. Mini-LEDs usually adopt conventional pick and place techniques including surface mounting technology. Every time the number of LEDs that can be transferred is limited. For Micro-LEDs, usually millions of LEDs need to be transferred when a heterogenous target substrate is used, therefore the number of LEDs to be transferred at a time is significantly larger, and thus disruptive mass transfer technique should be considered.

It is exciting to see all the kinds of display technologies which make our world colorful. We definitely believe that LCD and/or LED displays will pay very important roles in the future metaverse.
If you have any questions about Orient Display displays and touch panels. Please feel free to contact: Sales Inquiries, Customer Service or Technical Support.

Difference between resistive and capacitive touch panel

Capacitive Touch Screen

Projected capacitive touch screen contains X and Y electrodes with insulation layer between them. The transparent electrodes are normally made into diamond pattern with ITO and with metal bridge.

Human body is conductive because it contains water. Projected capacitive technology makes use of conductivity of human body. When a bare finger touches the sensor with the pattern of X and Y electrodes, a capacitance coupling happens between the human finger and the electrodes which makes change of the electrostatic capacitance between the X and Y electrodes. The touchscreen controller detects the electrostatic field change and the location.

Resistive Touch Screen

A resistive touch screen is made of a glass substrate as the bottom layer and a film substrate (normally, clear poly-carbonate or PET) as the top layer, each coated with a transparent conductive layer (ITO: Indium Tin Oxide), separated by spacer dots to make a small air gap. The two conducting layers of material (ITO) face each other. When a user touches the part of the screen with finger or a stylus, the conductive ITO thin layers contacted. It changes the resistance. The RTP controller detects the change and calculate the touch position. The point of contact is detected by this change in voltage.

Which Is Better Capacitive or Resistive Touchscreen?

  Resistive Touch Screen Capacitive Touch Screen
Manufacturing Process Simple More complicated
Cost Lower Higher: Depending on size, number of touches
Touch Screen Control Type Requires pressure on the touchscreen. Can sense proximity of finger.
Power Consumption Lower Higher
touch with thick gloves Always good more expensive, need special touch controller
Touch Points Single Touch Only Single, two, gesture or Multi-Touch 
Touch Sensitivity Low High (Adjustable)
Touch Resolution High Relatively low
Touch Material Any type Fingers. Can be designed to use other materials like glove, stylus, pencil etc.
False Touch Rejection False touches can result when two fingers touch the screen at same time. Good Performance
Immunity to EMI Good Need to special design for EMI
Image Clarity Less transparent and smoky looking Very high transparent especially with optical bonding and surface treatment
Sliders or Rotary Knobs Possible, but not easy to use Very good
Cover Glass None Flexible with different shapes, colors, holes etc.
Overlay Can be done No
Curve Surface Difficult Available
Size Small to medium Small to very big size
Immunity to Objects/Contaminants on Screen Good Need to special design to avoid false touch
Resistant to Chemical Cleaners No Good
Durability Good Excellent
Impact Ball Drop Test Surface film protected Need special design for smash
Scratch Resistance As high as 3H As high as 9H
UV Degradation Protection Less protection Very good

What Are Resistive Touch Screens Used For?

Resistive touch screens still reign in cost-sensitive applications. They also prevail in point-of-sale terminals, industrial, automotive, and medical applications.

What Are Capacitive Touch Screens Used For?

Projected Capacitive Touch Panel (PCAP) was actually invented 10 years earlier than the first resistive touchscreen. But it was no popular until Apple first used it in iPhone in 2007. After that, PCAP dominates the touch market, such as mobile phones, IT, automotive, home appliances, industrial, IoT, military, aviation, ATMs, kiosks, Android cell phones etc.

If you have any questions about Orient Display capacitive touch panels. Please feel free to contact: Sales Inquiries, Customer Service or Technical Support.

Emulating Embedded Linux Systems with QEMU

Emulating Embedded Linux Systems with QEMU


1. Introduction

Embedded software development relies on embedded hardware devices, such as development boards, external module devices, etc., but if the debugging work has nothing to do with peripherals, only the kernel debugging can be simulated using QEMU without purchasing hardware.

It’s available for Linux and Windows hosts and emulated PowerPC, ARM, MIPS, and SPARC targets. QEMU takes the approach of providing a minimal translation layer between the host and target processor. The host processor is the one running the emulator, and the target processor is what’s being emulated.

The following is a detailed introduction to the process of setting up QEMU development environment.


2. Environment

2.1 Used environment

* Ubuntu-18.04.1


* PC:Windows10

* Virtual Machine:VirtualBox-5.18

* Virtual OS:Ubuntu-18.04.1

* Simulated development board: vexpres

2.2 Tools used when setting up the environment

* qemu-4.2.0

* linux-4.14.172 (Linux Kernel)

* u-boot-2017.05

* busybox-1.31.1

* arm-linux-gnueabi-gcc

Put all related files in  /home/joe/qemu

3. Install cross-compilation tools

# sudo apt install gcc-arm-linux-gnueabi


Check if the installation is successful

$ arm-linux-gnueabi-gcc -v

Using built-inspecs.



Target: arm-linux-gnueabi

Configured with: ../src/configure -v –with-pkgversion=’Ubuntu/Linaro 7.5.0-3ubuntu1~18.04′–with-bugurl=file:///usr

Thread model: posix

gcc version 7.5.0(Ubuntu/Linaro 7.5.0-3ubuntu1~18.04)


4. Configure and Compile the Linux kernel

4.1 Download Linux Kernel

Download the required kernel version from

Here I download the relatively latest long-term supported kernel version linux-4.4.157

wget  to /qemu directory

4.2 Unzip the Linux kernel

# tar xvJf linux-4.4.157.tar.xz

4.3 Compile Linux Kernel

// Enter the kernel source file directory

# cd linux-4.4.157

make CROSS_COMPILE=arm-linux-gnueabi- ARCH=arm vexpress_defconfig

make CROSS_COMPILE=arm-linux-gnueabi- ARCH=arm menuconfig

If running menuconfig shows that the ncurses package is missing, just run the following command to install it)

$ sudo apt-get install libncurses5-dev

Enter the menu configuration and make the following settings

Compile with cross toolchain

After successful compilation, Generate a kernel image file under the directory

arch/arm/boot, zImage and dtb can be copied into a separate folder for convenient use


5. Install QEMU Tools

5.1 Install QEMU

* wget

* tar xvJf qemu-4.2.0.tar.xz

* cd qemu-4.2.0

5.2 Install dependent packages before configuring QEMU

# apt install zlib1g-dev
# apt install libglib2.0-0 libglib2.0-dev
# apt install libsdl1.2-dev
# apt install libpixman-1-dev libfdt-dev

In order to prevent the files from being messy after compilation, create the builder directory as the intermediate target path for compilation.

Configure, compile and install QEMU.

5.3 Configure QEMU to support all boards under the arm architecture

# ../configure –target-list=arm-softmmu –audio-drv-list=

If pixman is missing when the following prompt appears,

use sudo apt-get install libpixman-1-dev to install it.

5.4 View QEMU version

5.5 View development boards supported by QEMU

5.6 Run QEMU

# qemu-system-arm -M vexpress-a9 -m 512M -kernel ./zImage -dtb ./vexpress-v2p-ca9.dtb -nographic -append “console=ttyAMA0”




# qemu-system-arm -M vexpress-a9 -m 512M -kernel linux-.4.157/arch/arm/boot/zImage -dtb linux-4.4.157/arch/arm/boot/dts/vexpress-v2p-ca9.dtb -nographic -append “console=ttyAMA0”

In order to better testing and start qemu, you can create the startup script, and give the script permission to run chmod +x




qemu-system-arm \

-M vexpress-a9 \

-m 512M \

-kernel /home/joe/jemu/linux-4.4.157/arch/arm/boot/zImage \

-dtb /home/joe/jemu/linux-4.4.157/arch/arm/boot/dts/vexpress-v2p-ca9.dtb \

-nographic \

-append “console=ttyAMA0”


6. Make a root file system

Use busybox to make a simple root file system.

6.1 Download busybox tool

Download busybox from

# wget

# tar xjvf busybox-1.31.1.tar.bz2

# cd busybox-1.31.1

# make defconfig

# make CROSS_COMPILE=arm-linux-gnueabi-

# make install CROSS_COMPILE=arm-linux-gnueabi-

The following information is prompted, indicating that the installation is successful.

After the installation is complete, the generated target file defaults to the ./_install directory.


6.2 Generate root file system

6.2.1 compile and install busybox

# mkdir rootfs

# sudo cp -r _install/* rootfs/

6.2.2 Add glibc library, add loader and dynamic library in the root file system

# sudo cp -r _install/* rootfs/

# sudo cp -p /usr/arm-linux-gnueabi/lib/* rootfs/lib/

6.2.3 Create 4 tty terminal devices (c stands for character device, 4 is the major device number, and 1~4 are the minor device numbers respectively)


6.3 Make SD card file system image

6.3.1 Generate an empty SD card image

# dd if=/dev/zero of=rootfs.ext3 bs=1M count=32

6.3.2 Format SD card as exts file system

# mkfs.ext3 rootfs.ext3

6.3.3 Burn rootfs to SD card

# sudo mount -t ext3 rootfs.ext3 /mnt -o loop

# sudo cp -rf rootfs/* /mnt/

# sudo umount /mnt


7. Verify

7.1 Start Qemu

Run the following command to test, check if the compiled kernel can run successfully

# sudo qemu-system-arm -M vexpress-a9 -m 512M -kernel ~/qemu/zImage –dtb ~/qemu/vexpress-v2p-ca9.dtb -nographic -append “console=ttyAMA0”

Or using Script:


In the above test, the kernel will report panic, suggesting that we lack the root file system.

The above problem is due to the busybox tool generated inn the x86 environment.

We used make install when install busybox, so you should use

make ARCH=arm CROSS_COMPILE=arm-linux-gnueabi- install


The compilation tool generates the busybox tool used by the arm platform

# file rootfs/bin/busybox

rootfs/bin/busybox: ELF 32-bit LSB executable, ARM, EABI5 version 1 (SYSV), dynamically linked, interpreter /lib/ld-, for GNU/Linux 3.2.0, BuildID[sha1]=cbcd33b8d6c946cb19408a5e8e714de554c87f52, stripped


7.2 Verify again

Now, Qemu has started the Linux kernel and mounted the file system successfully, and can interact with the system with simple functions through the serial terminal. The problem of not being able to run /etc/init.d/rcS in the printing process, you only need to add the /etc/init.d/rcS file. The content of the file can be a prompt statement.


7.3 Exit QEMU

Two ways to exit qemu

* In another terminal input: kill all qemu-system-arm

* In Qemu input:  Ctrl+ A; X

QEMU: Terminated


8. Start the Linux kernel through u-boot

Embedded system usually include: u-boot, kernel, rootfs, and appfs. The positional relationship of these parts on the ARM development board shown in the figure below


BootLoader BootParameters Kernel Rootfs Appfs


Rootfs can run in board or PC


8.1 Prepare U-boot

8.1.1 Download u-boot,   we use: u-boot-2021.01.tar.bz2

# tar -jxvf u-boot-2018.09.tar.bz2

8.1.2 Compile u-boot

# vim Makefile

CROSS_COMPILE = arm-linux-gnueabi-

# vim

ARCH = arm

# make vexpress_ca9x4_defconfig, error

Need :  sudo apt install bison

sudo apt install flex

then:     # make -j4    error

Need :   export CROSS_COMPILE=arm-linux-gnueabi-

export ARCH=arm

again:  # make vexpress_ca9x4_defconfig

# make -j4


 8.1.3 Test, start u-boot

$ sudo qemu-system-arm -M vexpress-a9 -m 512M -kernel u-boot-2021.01/u-boot –nographic


8.2 Kernel configuration compilation

Use u-boot to boot the kernel image:

Need to compile the kernel into uImage format,

Need to specify the load address of uImage in memory

Specify when compiling the kernel: make LOADADDR=? uImage -j4


# cd /home/joe/qemu/linux-4.4.157

# make LOADADDR=0x60003000 uImage -j4


After u-boot compilation is finished, a mkimage file will be generated under the tool folder, copy this file to the bin folder under the cross compiler directory.

$ cd qemu/linux-4.4.157


$ sudo apt install u-boot-tools

Get uImage

9. QEMU network function settings

When the Qemu virtual machine starts on u-boot, uImage needs to be loaded into the memory, and uImage can be downloaded to the specified address in the memory through the TFTP server.

9.1 Check whether the host kernel supports the tun/tap module

// Install the two tools that the bridged network depends on

# sudo apt install uml-utilities bridge-utils

Create tun device file: /dev/net/tun (usually created automatically)

Modify the /etc/network/interfaces (configure the network, restart to take effect)

# sudo vim /etc/network/interfaces

auto loiface lo inet loopbackauto enp0s3          // name of virtual network cardauto br0iface br0 inet dhcpbridge_ports enp0s3


9.2 Reboot

# reboot

Then check Qemu’s network environment

The virtual network port br0 is the network port for the communication between the Qemu virtual machine and the Linux host.


10. Install TFTP server

Create a TFTP server to download uImage to the memory when launching uImage for the Qemu simulation development board


10.1 Install tftp tool


$ apt-get install tftp-hpa tftpd-hpa xinetd


10.2 Modify the configuration file and set the TFTP server directory

# sudo vim /etc/default/tftpd-hpa




10.3 Create a tftp directory on the Linux host

# mkdir /home/joe/tftpboot

# chmod 777 /home/joe/tftpboot


10.4 Restart the tftp service

# sudo /etc/init.d/tftpd-hpa restart


10.5 Set kernel startup parameters in u-boot

copy uImage and cexpress-v2p-ca9.dtb to tftpboot

Start Qemu to verify


$ sudo qemu-system-arm -M vexpress-a9 -m 512M -kernel u-boot-2021.01/u-boot –nographic -net nic,vlan=0 -net tap,vlan=0,ifname=tap0 -sd rootfs.ext3


Now, the rootfs directory is a simple root file system, which can be made into a mirror file, and the mirror file can be burned to the development board, or the Linux kernel can be started by u-boot in Qemu and mounted on the mirror file. It can also be set to boot via NFS network file system.


11. Mount NFS file system

11.1 Install and configure NFS service

11.1.1 Install

$ sudo apt install nfs-kernel-server


11.1.2  Configutation

$ sudo mkdir /home/joe/qemu/rootfs

$ sudo chown nobody:nogroup /home/joe/qemu/rootfs

$ sudo chmod 777 /home/joe/qemu/rootfs

$ sudo nano /etc/exports

Add:  /home/joe/qemu/rootfs *(rw,sync,no_root_squash)


Restart nfs server:

$ sudo /etc/init.d/nfs-kernel-server  restart

Or: $systemctl restart nfs-kernel-server


Check whether the NFS shared directory is created

$ sudo showmount –e

When using the NFS network file system, the Linux host needs to close the system firewall, otherwise, abnormalities will occur when the system is running.



Hopefully, with the help of this blog, you know more about QEMU. All the techniques demonstrated above were used in various submissions to our program. There’s not a single, fixed way to emulate with QEMU. Explore different techniques and see what works for you. Familiarize yourself with the knowledge and you will be surprised at how it can help you in unexpected ways.

Pros and Cons of Resistive Touchscreens

A resistive touch screen is made of a glass substrate as the bottom layer and a film substrate (normally, clear poly-carbonate or PET) as the top layer, each coated with a transparent conductive layer (ITO: Indium Tin Oxide), separated by spacer dots to make a small air gap. The two conducting layers of material (ITO) face each other. When a user touches the part of the screen with finger or a stylus, the conductive ITO thin layers contacted. It changes the resistance. The RTP controller detects the change and calculate the touch position. The point of contact is detected by this change in voltage.

Pros of Resistive Touchscreen

One of the main reasons why resistive touch panels still exist is its simple manufacturing process and low production cost. The MOQ (Minimum Order Quantity) and NRE (Non-Recurring Expense) are low. The driving is simple and low cost. The power consumption is low too. Resistive touch panel also immune to EMI well. Although it can’t use cover lens at the surface, the overlay can make it flexible for designs.

Resistive touchscreens offer an unparalleled level of durability. Manufacturing companies, restaurants and retailers often prefer them over other types of touchscreens for this very reason. With their durable construction, resistive touchscreens can withstand moisture and stress without succumbing to damage.

You can control a resistive touchscreen using a stylus or while wearing gloves. Most capacitive touchscreens only register commands performed with a bare finger (or a special capacitive stylus). If you use a stylus or a gloved finger to tap the interface, the capacitive touchscreen won’t respond to your command. Resistive touchscreens register and respond to all forms of input, though. You can control them with a bare finger, a gloved finger, a stylus or pretty much any other object.

Cons of Resistive Touchscreen

The biggest advantages for resistive touch panel are its touch experience and clarity. It can only be used for single touch, no gestures or multi-touch. False touches can be generated if using two or more fingers to touch it.

Resistive touch panel’s transparency is relatively low. In order to prevent Newton rings or fingerprint mark, sometimes AG(anti-glare) film has to be used to make it look more smoky. Optical bonding can’t be used for RTP. The surface of resistive touch panel is soft and easily get scratched.

There are still a few potential cons associated with resistive touchscreens. When compared to capacitive touchscreens, resistive touchscreens aren’t as sensitive. They are still responsive, but you’ll have to tap or press the interface with greater force for a resistive touchscreen to recognize your input.

Resistive touchscreens usually offer lower display resolutions than capacitive touchscreens. Granted, not all applications require a high-resolution display. If a touchscreen is used as a point-of-sale (POS) system in a retail environment, for example, resolution shouldn’t be a concern.

If you have any questions about Orient Display capacitive touch panels. Please feel free to contact: Sales Inquiries, Customer Service or Technical Support.

Pros and Cons of Capacitive Touchscreens

Capacitive Touch Screen (PCAP)

Projected capacitive touchscreen contains X and Y electrodes with insulation layer between them. The transparent electrodes are normally made into diamond pattern with ITO and with metal bridge.

Human body is conductive because it contains water. Projected capacitive technology makes use of conductivity of human body. When a bare finger touches the sensor with the pattern of X and Y electrodes, a capacitance coupling happens between the human finger and the electrodes which makes change of the electrostatic capacitance between the X and Y electrodes. The touchscreen controller detects the electrostatic field change and the location.

Pros of Capacitive Touchscreen (CTP)

  • Looks sharper and brighter

    Capacitive Touch Screen uses glass substrate which has high transparency compared with plastic film used by resistive touch panels. Plus, optical bonding and glass surface treatment which make CTP good picture quality and contrast.
  • Better Human Machine Experience

    Because capacitive touchscreens register touch via the human body’s electrical current, they require less operating pressure than resistive touch panel glass. It supports touch gestures and multi-touch which makes it much better user experience of touch.
  • Incredible durability

    Because the cover glass is used in front which can be extremely high hardness (>9H), it is extremely durable for touch which can exceed 10 million touches. It also prevents from scratches and easy to clean which makes it prevailing resistive touch panels.
  • Size and Appearance

    Capacitive touchscreen can be made for very large size (100 inches) and the cover lens can be decorated with different colors, shapes, holes to provide users flexible designs.

Cons of Capacitive Touchscreen (CTP)

  • Cost

    Capacitive Touchscreen manufacturing process is relatively more expensive and the cost can be high.
  • Immunity to Objects/Contaminants on Screen

    Capacitive Touchscreen needs special design and uses special controllers to make it used in special applications, such as using glove to touch, or with water, salt water environment. The cost can be even higher.
  • Damage

    The cover lens can crack. In order to prevent glass debris to fly, a film or optical bonding is needed in the manufacturing process to make the price even higher.
  • Interferes

    Capacitive Touchscreen is easily to be affected by ESD or EMI, special designs have to be considered in the design which can drive the price higher. Special calibration has to be carried out with the help of the controller manufacturer.
  • Power and wake up

    The power used in capacitive Touchscreen can be higher than resistive touch panel. Sometimes, a hot button has to be designed to wake up the touch function.

If you have any questions about Orient Display capacitive touch panels. Please feel free to contact: Sales Inquiries, Customer Service or Technical Support.

How to fix LCD display problems?


LCD screen display problem why does it occur?

Liquid crystal displays (LCDs) are the most widely used display technology. Their applications cover TV, mobile phone, appliances, automotive, smart home, industrial meters, consumer electronics, POS, marine, aerospace, military etc. LCD screen display problem can occur for several reasons.

  • Effect of environmental conditions on the LCD assembly. Environmental conditions include both the effects of temperature and humidity, and cyclic loading.
  • Effects of handling conditions on the LCD. Handling can include bending, repetitive shock, and drop loading conditions.
  • Effect of manufacturing process. With the development of LCD for more than 40 years and the modern manufacturing equipment, this kind if defects are getting rear.

Common failures seen in LCDs are a decrease in screen contrast, non-functioning pixels or the whole display, and broken glass. Different kinds of LCD display problem need to have different kinds of fix methods or make the decision not worthwhile to repair.

LCD display problem – How to fix it?

  • Broken glassIf you accidently drop the LCD and you find it broken on the surface but the display still works. You might just break the touch panel; you can find a repair house or find a youtube video to replace the touch panel. If you find the display not showing, especially you find the fluid leaking out. You need to reply the whole display modules.
  • Dim LCD displayLCD can’t emit light itself. It uses backlight. Normally, the backlight is not fully driven, you can increase the LED backlight to make a dim LCD display brighter. But if you LCD display has been used for a long time, it is possible that the LED backlight has to be the end of life (not brightness enough) if you turn on 100% backlight brightness. In that case to fix LCD screen, you have to find a way to change the backlight. For some display, it is an easy job but it can be difficult for other displays depending on the manufacturing process.
  • Image sticking (Ghosting)Sometimes, you will find the previous image still appearing at the background even if you change to another image. It is also called burn in. This kind of failure doesn’t need to repair by professionals. You can simply shut off the display overnight, this kind of problem will go away. Please do remember that displaying a static image for a long time should be avoided.
    Display including backlight completely dead

    LCD screen display problem – the most common cases

    With the modern manufacturing process and design, this kind of failure rarely happens. Normally, it is caused by no power. Please check if the battery dead or adapter (power supply) failure or even check if you have plug in firmly or with the wrong power supply. 99% the display will be back on.

  • LCD has white screen – If a LCD has a white screen which means the backlight is good. Simply check your signal input sources which are the most causes. It can also be caused by the display totally damaged by ESD or excess heat, shock which make the LCD controller broken or the connection failure which has to be repaired by professionals.
  • Blur ImagesAs the LCD images are made of RGB pixels, the screen shouldn’t be blur like old CRT displays. If you do see blur images, they might be caused by two reasons. 1) LCD has certain response time, if you are playing games or watch fast action movies, some old LCD displays can have image delays. 2) The surface of the LCD is made of a layer of plastic film with maximum hardness of 3H. If you clean the surface often or use the wrong detergent or solvent which cause the surface damage. To fix damage on LED screen it’s need to be changed with professionals.

If you have any questions about Orient Display displays and touch panels. Please feel free to contact: Sales Inquiries, Customer Service or Technical Support.

Check Also: Bistable LCD

Introduction of Lichee Pi

Introduction of Lichee Pi

The LicheePi is a delicate, single-board computer, running on the low-cost Allwinner V3S platform which is popularity in recent years. It can be used for beginners to learn Linux or for product development. it offers a wealth of peripherals (LCD, ETH, UART, SPI, I2C, PWM, SDIO…) and powerful performance.



        Lichee Zero                                  Lichee Nano





                                 Lichee Pi Zero                                                                          Lichee Pi Nano 






SoC Allwinner V3S Allwinner F1C100S
CPU ARM Cortex-A7 ARM9
Operating Freq. 1.2GHz 408MHz
Storage SPI Flash/Micro-SD SPI Flash/Micro-SD



* Universal 40P RGB LCD FPC:

* Supported resolutions: 272×480, 480×800,1024×600

* Onboard RTP chip, supports a touch screen

* Universal 40P RGB LCD FPC:

* Supported resolutions: 272×480, 480×800,1024×600

* Onboard RTP chip, supports a touch screen



* SDIO x2
* SPI x1
* I2C x2
* UARTx3
* 100M Ether x1(include EPHY)
* OTG USB x1
* PWM x2
* LRADC x1
* Speakerx2 + Mic x1
* SDIO x1
* SPI x2
* TWIX x3
* UART x3
* OTG USB x1
* TV out* PWM x2
* LRADC x1
* Speakerx2 + Mic x1

Electrical Information


Micro USB 5V, 2.54mm pins 3.3V~5V power supply; 1.27mm stamp hole power supply.

1GHz linux IDLE run 90~100mA; cpu-burn run ~180mA

Storage Temperature -40~125

Operating Temperature -20~70

Micro USB 5V, 2.54mm pins 3.3V~5V power supply; 1.27mm stamp hole power supply.

408MHz linux IDLE run 90~54mA; with screen operating current ~250mA

Storage Temperature -40~125

Operating Temperature -20~70


The temperature when running the Linux stress test is only slightly higher than the body temperature.


Lichee Pi support many OS such as: Linux, RT-Tread, Xboot or no OS.

Like most MCU, the Lichee Pi can connect to several low-speed interfaces, such as GPIO, UART, PWM, ADC, I2C, SPI, and more. Moreover, it can run other high-speed peripherals such as RGB LCD, EPHY, MIPI CSI, OTG USB, and more. The Lichee Pi has an integrated codec that allows direct connection to a headphone or microphone.


Display Connector:

The universal 40P LCD comes with a led back light and four-wire lines, electrical resistance touch, which is very suitable for display and interaction. A13 also supports four-wire resistance touch function, can carry out two-point touch detection.


This interface is compatible with the interface of ORIENT DISPLAY products.










Lichee Pi Link:
Telegram group:

How does a Graphic LCD work?

An Introduction to Graphic LCD Displays

Graphic LCD Displays normally refer to monochrome graphics LCD displays or dot matrix LCD displays. Although color TFT (Thin Film Transistor) and OLED (Organic Light Emitting Diodes) displays to meet all the definitions of graphic LCD displays and can also be categorized as graphic LCD displays, monochrome graphics LCD displays have been in the market much earlier than color TFT displays and they become the legacy type of display. That is the reason that Graphic LCD displays only refer to monochrome, not the full color.

What are Graphic LCD Displays?

Compared with Character LCD Displays which can only display digits or alphanumeric, graphic LCD displays can display digits, alphanumeric, and graphics. They played very important roles in the early stages of LCD display history.

Graphic LCD displays are identified by the number of pixels in vertical and horizontal directions. For example, 128 x 64 dot matrix graphic display has 128 dots/pixels along the X axis, or horizontal, and 64 dots/pixels along the Y-axis or Vertical. Each of these dots sometimes referred to as a pixel, can be turned ON and OFF independently of each other. The customer makes use of software to tell each dot when to turn ON and OFF. The early engineering work has to light/map pixel by pixel, which is very tedious work. Thanks to the LCD controller advancement, Some Orient Display graphic LCD products have many images in the memory already which greatly helps engineers to reduce the workload and make the products much faster to the market. Please check with our engineers for details.

Orient Display provides dot matrix formats of 122×32, 128×64, 128×128, 160×32, 160×64, 160×160, 192×48, 192×64,202×32, 240×64, 240×160, 240×128, 282×128, 320×240 etc.

Graphic LCD Interface

There are some popular graphic LCD interfaces, such as 8 bit or 16 bit 6800 and/or 8080 MCU interface, 3 or 4 wire SPI interface, I2C interface etc.

Fluid Options of a Graphic LCD Display

There are many options for graphic LCD displays, all of them derived from STN (Super-Twisted Nematic Display). TN (Twisted Nematic Display) or HTN (High-performance TN) displays are rarely used in graphic LCD displays because of their poor contrast and narrow viewing angles.

  • Positive displays can include: yellow-green STN, gray STN, positive FSTN;
  • Negative displays can include: blue STN, negative FSTN, FFSTN, ASTN;

Backlight Options of a Graphic LCD Display

LCD itself can’t emit light. In order to be observed under the dim light, the backlight has to be used. Back to 10 years ago, Backlight can be LED (Light Emitting Diode), CCFL (Cold Cathode Fluorescent Lamps) or EL (Electroluminescent) backlight. Thanks to the development of LED technology, especially the breakthrough of the blue and white LED technologies, LED backlight dominates the market. LED backlight can be made either bottom lit and side lit with various colors For more information, please refer to Orient Display Jazz Graphic LCD Display and Backlights.

Graphic LCD Display Controller and Drivers

The LCD controller is a small microprocessor that converts the customer’s software code (aka firmware) to information that the LCD can understand. LCD Drivers control the complex AC voltage requirements for the LCDs and they need a LCD controller to keep refreshing the individual pixel information to their drive circuitry. These ICs will typically be integrated into the LCD Modules either by COG (Chip on Glass) or COB (Chip on Board) technologies.

Sitronix is the world’s biggest graphic LCD controller manufacturers. The headache for most engineers is that LCD controllers can EOL (End of Life) a lot. Please make sure to discuss with Orient Display engineers for the most updated information to keep 5-10 years supply life.