tft lcd flicker quotation

I got the 3.95" LCD from aliexpress which uses IL9488. I used the MCUFRIEND_kbv library. I am using an Arduino Mega as I need other GPIO to be used for other purposes. I can"t use the Uno because of this limitation.

I have other modules like the DS3231, and ESP8266 connected to the Mega and this 3.95" LCD connected as well. ESP8266 is powered separately using a 12-5V converted supply. The Mega is powered using another source. The normal graphics test is working in the LCD. I am able to make it work with the Nano, Uno and Mega. Even for the Mega I am able to write customized messages.

Every update (LCD display function is from the loop which sets the text when there is a second/time/hour difference in the time) seems like it draining more current as the one of the LED connected to Mega dims, the Rx/Tx LEDs also dim.

I am able to get the LCD refreshed but it shows a flickering. I powered the LCD 3.3V and 5V using another separate source but still the small flickering continues.

Moreover all these time I was connected to the Mega through the USB from the laptop. Once I unplug the USB, LCD starts and shows some update and again become white. This continues and an not able to see anything on LCD there after.

I am not sure why only when the Mega is connected to USB this LCD works and that too flickering but once the USB is removed the LCD is not working at all.

To investigate the flickering more you can set breakpoints inside the function "GrpDrv_SetFrameBuffer" in the file /Common/Source/FreeRTOS/StreamRuntime_GraphicRZA.cpp. In this function a call to "R_RVAPI_GraphChangeSurfaceVDC" is done which will effectively change the framebuffer which is currently displayed.

In the past decade, LCD monitors have replaced CRT screens for all but the most specialist applications. Although liquid crystal displays boast perfect

eitherway I have a sligh issue, even with FSMC which makes writes very fast when i want to write something, Say I want to have a cube going up and down or i want to load an image, you can sometimes see a sligh flicker or the drawing line for the image, Or when I have my cube example I have to draw a cube in the background color behind it to get rid of the old stuff, if I use my clear function it just flickers.

eitherway I have a sligh issue, even with FSMC which makes writes very fast when i want to write something, Say I want to have a cube going up and down or i want to load an image, you can sometimes see a sligh flicker or the drawing line for the image, Or when I have my cube example I have to draw a cube in the background color behind it to get rid of the old stuff, if I use my clear function it just flickers.

Golden View Display wants you to make an informed choice among our LCD products. The tech center provides you with most of the information you will need to understand liquid crystal displays.

The tft (thin film transistor), a thin film field effect transistor, is one of the active matrix liquid crystal displays. It can “actively” control each individual pixel on the screen, which can greatly improve the response time. General tft response time is relatively fast, about 80 milliseconds, and the viewing angle is large, generally can reach about 130 degrees, mainly used in high-end products. The so-called thin film field effect transistor means that each liquid crystal pixel point on the LCD is driven by a thin film transistor integrated in the back. tft belongs to the active matrix LCD, which technically adopts the “active matrix” method to drive, by using the thin film technology to make the electrode of the transistor, and using the scanning method to “actively pull “The light source is first transmitted upward through the lower polarizing plate when irradiated, and the light is conducted by the liquid crystal molecules to achieve the purpose of display through shading and light transmission.

TFT in active matrix liquid crystal display, in the technology used zhuan active shu matrix way to drive, the method genus is the use of thin film technology made of electro crystal electrodes, the use of scanning method active pull control any one display point on and off, light source irradiation first through the lower polarizing plate upward transmission, with the help of liquid crystal molecules to conduct light, through shading and light transmission to achieve the purpose of the display.

TFT also improves the phenomenon that STN will flicker (water ripple) blur, effectively improving the ability to play dynamic images. Compared with STN TFT has excellent color saturation, reproduction ability and higher contrast ratio.

1, the use of TFT LCD module design products, pay attention to the perspective of the liquid crystal and the design of the product use consistent with.

2, to prevent damage to the LCD glass, falling or hard object impact will cause the LCD screen rupture or shatter, especially the corners of the part is particularly fragile.

3, the surface of the LCD polarizer has a surface layer to inhibit reflection, must not scratch the surface, it is best to use transparent plastic material on the surface of the LCD to protect the screen.

4, if the LCD module storage below the specified temperature below, the liquid crystal material will condense performance will also be weakened. If the LCD module is stored above the specified temperature, the molecular arrangement direction of the liquid crystal material will change to liquid state and may not be able to recover to the original state. Exceeding the temperature and humidity range will cause the polarizer to peel or blister. Therefore, liquid crystal modules should be stored in the specified temperature range.

In this Arduino touch screen tutorial we will learn how to use TFT LCD Touch Screen with Arduino. You can watch the following video or read the written tutorial below.

As an example I am using a 3.2” TFT Touch Screen in a combination with a TFT LCD Arduino Mega Shield. We need a shield because the TFT Touch screen works at 3.3V and the Arduino Mega outputs are 5 V. For the first example I have the HC-SR04 ultrasonic sensor, then for the second example an RGB LED with three resistors and a push button for the game example. Also I had to make a custom made pin header like this, by soldering pin headers and bend on of them so I could insert them in between the Arduino Board and the TFT Shield.

Here’s the circuit schematic. We will use the GND pin, the digital pins from 8 to 13, as well as the pin number 14. As the 5V pins are already used by the TFT Screen I will use the pin number 13 as VCC, by setting it right away high in the setup section of code.

I will use the UTFT and URTouch libraries made by Henning Karlsen. Here I would like to say thanks to him for the incredible work he has done. The libraries enable really easy use of the TFT Screens, and they work with many different TFT screens sizes, shields and controllers. You can download these libraries from his website, RinkyDinkElectronics.com and also find a lot of demo examples and detailed documentation of how to use them.

After we include the libraries we need to create UTFT and URTouch objects. The parameters of these objects depends on the model of the TFT Screen and Shield and these details can be also found in the documentation of the libraries.

So now I will explain how we can make the home screen of the program. With the setBackColor() function we need to set the background color of the text, black one in our case. Then we need to set the color to white, set the big font and using the print() function, we will print the string “Arduino TFT Tutorial” at the center of the screen and 10 pixels  down the Y – Axis of the screen. Next we will set the color to red and draw the red line below the text. After that we need to set the color back to white, and print the two other strings, “by HowToMechatronics.com” using the small font and “Select Example” using the big font.

Screen flickering is due to changes in brightness that occur when the cathode ray tube projects on the screen while its refresh rate is low. The number of times the display hardware updates its buffers in one second is called the refresh rate. Generally speaking, the variation of brightness mainly occurs between cathode ray tubes.

With a refresh rate below 60 Hz, most screens will produce flicker visible to the naked eye, but a refresh rate between 70-80 Hz can make the screen almost flicker-free. If the refresh rate exceeds 120 Hz, the flicker cannot be seen by the naked eye. We call it flicker-free.

LCD is divided into two CCFL backlights and an LED backlight. When the LCD display uses a CCFL backlight, the backlight power off, the lamp will continue to emit light for about a few milliseconds. The characteristics of the LED backlight allow it to control the speed of switching on and off the power supply more quickly to avoid continuous lighting when the power is off. Consequently, the LED backlight flashing screen will be more prominent than the CCFL backlight.

LCD is easily disturbed by a strong electric field or magnetic field, and sometimes the screen jitter is caused by the magnetic field or electric field near the LCD. To liquid crystal display ruled out clean everything around interference, move the computer to an empty table, then start boot test, if the screen computing phenomenon disappears. It means that your computer where you found it has a strong electric field or magnetic field interference. Please send suspiciously (e.g., speakers of the subwoofer, power transformers, magnetizing cup, etc.) from a computer nearby.

Please turn off the LCD and turn it back on a few times to degaussing. (today’s monitors have automatic degaussing when turned on.) LCD screen flashing reason: LCD screen refresh rate problem & LCD display and video card hardware problems display.

The main reason for the LCD screen dither is the LCD refresh frequency set lower than 75Hz caused by, at this time, the screen often appear dither, flicker phenomenon, and we only need to put the refresh rate to 75Hz above. The phenomenon of the screen dither will not occur.

The frequency of the LCD screen itself is too high, which leads to screen flashing. Generally, a few real-life problems cause screen flashing due to high frequency. People’sPeople’s naked eyes have no flicker feeling for the picture over 60hz, while the design standard of the general LCD screen is basically maintained on this data, so the frequency will not be too high under normal circumstances, but at the same time, the screen itself can not be ruled out fault. After the relevant instrument measurement is indeed the fault of the screen itself, in addition to the replacement of a new monochrome LCD screen is the design of equipment-related software.

LCD and light source frequency close to the situation of the splash screen is very common, because the frequency of the different light sources is different, in certain cases, the frequency of the LCD screen and artificial light similar flicker is also more common, the best way at this time is a kind of artificial light or LCD equipment, avoid the splash screen.

A video card that isn’t properly seated on the motherboard can cause many problems, including a screen flicker. Turn the computer off and then open the case, remove the video card and connect the monitor cable to a second video card you have replaced the old one with. If the problem persists, the issue isn’t the card–it’s something else.

LCD, although the price is not high, there are various problems. It will have multiple effects on our work and life. In ordinary life, when using LCD, as long as pay attention to the following points will extend the life of LCD.

All the screens flicker when it works. But we don’t see it all the time because it flashes too fast to catch the flickering in our eyes. When the screen’s refresh rate gets slow, we see the screen flickering. The causes behind screen flickering are very common properties. That’s why we always need to keep our device updated and clear the virus from the device to get a flicker less display.

The wide range of conditions over which LCD monitors are used means that it is desirable to produce displays whose luminance (brightness) can be altered to match both bright and dim environments. This allows a user to set the screen to a comfortable level of brightness depending on their working conditions and ambient lighting. Manufacturers will normally quote a maximum brightness figure in their display specification, but it is also important to consider the lower range of adjustments possible from the screen as you would probably never want to use it at its highest setting. Indeed with specs often ranging up to 500 cd/m2, you will certainly need to use the screen at something a little less harsh on the eyes. As a reminder, we test the full range of backlight adjustments and the corresponding brightness values during each of our reviews. During our calibration process as well we try to adjust the screen to a setting of 120 cd/m2 which is considered the recommended luminance for an LCD monitor in normal lighting conditions. This process helps to give you an idea of what adjustments you need to make to the screen in order to return a luminance which you might actually want to use day to day.

Changing the display luminance is achieved by reducing the total light output for both CCFL- and LED-based backlights. By far the most prevalent technique for dimming the backlight is called Pulse Width Modulation (PWM), which has been in use for many years in desktop and laptop displays. However, this technique is not without some issues and the introduction of displays with high brightness levels and the popularisation of LED backlights has made the side-effects of PWM more visible than before, and in some cases may be a source of visible flicker, eyestrain, eye fatigue, headaches and other associated issues for people sensitive to it. This article is not intended to alarm, but is intended to show how PWM works and why it is used, as well as how to test a display to see its effects more clearly. We will also take a look at the methods some manufacturers are now adopting to address these concerns and provide flicker-free backlights instead. As awareness grows, more and more manufacturers are focusing on eye health with their monitor ranges.

1) Frequency –The backlight is cycled on and off very rapidly, and this cycling typically occurs at a fixed frequency (in Hz). How fast this cycling occurs can impact whether flicker is visible or perceivable to the user, with higher frequencies being potentially less problematic. PWM has been known to operate at low frequencies of 180 – 240Hz for example which are likely to be more problematic than higher frequencies ranging up in to the Kilohertz range (e.g. 18,000Hz).

3) Duty Cycle – The fraction of each cycle for which the backlight is in an “on” state is called the duty cycle. By altering this duty cycle the total light output of the backlight can be changed. As you reduce the brightness to reach a lower luminance, the duty cycle becomes progressively shorter, and the time for which the backlight is on becomes shorter, while the time for which it is off is longer. This technique works visually since cycling the backlight on and off sufficiently fast means the user cannot see this flickering, because it lies above their flicker-fusion threshold (more on this later).

The analogue (non-PWM) graphs corresponding to these perceived luminance levels would appear as shown below. In this case there is no modulation. This is the method used for flicker-free backlights which we will discuss more a little later.

CCFL backlights can be dimmed by reducing the current through the bulb, but only by about a factor of 2 because of their strict current and voltage requirements. This leaves PWM as the only simple method of achieving a large range of luminance. A CCFL bulb is in fact normally driven by the inverter to cycle on and off at a rate in the 10’s of kilohertz and well outside the range of flicker visible to humans. However, the PWM cycling typically occurs at a much lower frequency, around 175Hz, which can produce artefacts visible to humans.

While PWM is attractive to hardware makers for the reasons outlined above, it can also introduce distracting visual effects if not used carefully. Flicker from LED backlights is typically much more visible than for older CCFL backlights at the same duty cycle because the LED’s are able to switch on and off much faster, and do not continue to “glow” after the power is cut off. This means that where the CCFL backlight showed rather smooth luminance variation, the LED version shows sharper transitions between on and off states. This is why more recently the subject of PWM has cropped up online and in reviews, since more and more displays are moving to W-LED backlighting units now.

Where the effect of flicker can really come into play is any time the user’s eyes are moving. Under constant illumination with no flickering (e.g. sunlight) the image is smoothly blurred and is how we normally perceive motion. However, when combined with a light source using PWM several discrete afterimages of the screen may be perceived simultaneously and reduce readability and the ability of the eyes to lock onto objects. From the earlier analysis of the CCFL backlighting we know that false colour may be introduced as well, even when the original image is monochromatic. Below are shown examples of how text might appear while the eyes are moving horizontally under different backlights.

It is important to remember that this is entirely due to the backlight, and the display itself is showing a static image. Often it is said that humans cannot see more than 24 frames per second (fps), which is not true and actually corresponds to the approximate frame rate needed to perceive continuous motion. In fact, while the eyes are moving (such as when reading) it is possible to see the effects of flicker at several hundred hertz. The ability to observe flicker varies greatly between individuals, and even depends on where a user is looking since peripheral vision is most sensitive.

So how fast is PWM cycling backlights on and off? This seems to depend on the backlight type used, with CCFL-based backlights nearly all cycling at 175Hz or 175 times per second. LED backlights have been reported typically running from 180 – 420Hz, with those at the lower end flickering much more visibly. Some have even faster frequencies of >2000Hz so it really can vary. While this might seem too fast to be visible, keep in mind that 175Hz is not much faster than the 100-120Hz flicker observed in lights connected directly to the mains power.

100-120Hz flickering of fluorescent lights has in fact been linked to symptoms such as severe eye strain and headaches in a portion of the population, which is why high-frequency ballast circuits were developed that provide almost continuous output. Using PWM at low frequencies negates the advantages of using these better ballasts in backlights because it turns an almost constant light source back into one that flickers. An additional consideration is that poor quality or defective ballasts in fluorescent backlights can produce audible noise. In many cases this is exacerbated when PWM is introduced since the electronics are now dealing with an additional frequency at which power usage is changing.

It is also important to distinguish the difference between flicker in CRT displays and CCFL and LED backlit TFT displays. While a CRT may flicker as low as 60Hz, only a small strip is illuminated at any time as the electron gun scans from top to bottom. With CCFL and LED backlit TFT displays the entire screen surface illuminates at once, meaning much more light is emitted over a short time. This can be more distracting than in CRTs in some cases, especially if short duty cycles are used.

The flicker itself in display backlights may be subtle and not easily perceptible for some people, but the natural variation in human vision seems to make it clearly visible to others. With the use of high-brightness LED’s on the rise it is becoming increasingly necessary to use short PWM duty cycles to control brightness, making flicker more of a problem. With users spending many hours every day looking at their monitors, shouldn’t we consider the long term effects of both perceptible and imperceptible flicker?

If you find PWM backlight flickering distracting or just want to see if reducing it makes reading on a monitor easier, I’d encourage you to try the following: Turn the brightness of your monitor up to maximum and disable any automatic brightness adjustments. Now use the colour correction available in your video card drivers or calibration device to reduce the brightness to normal levels (usually by adjusting the contrast slider). This will reduce the luminance and contrast of your monitor while leaving the backlight on as much as possible during PWM cycles. While not a long-term solution for most due to the decreased contrast, this technique can help to discover if a reduction in PWM usage is helpful.

A much better method of course would be to purchase a display not relying on PWM for dimming, or at least one which uses a much higher cycling frequency. Few manufacturers seem to have implemented PWM at frequencies that would limit visible artefacts (well above 500Hz for CCFL and above 2000 Hz for LED). Additionally, some displays using PWM do not use a 100% duty cycle even at full brightness, meaning they will always produce flicker. Several LED-based displays may in fact be currently available which do not use PWM, but until backlight frequency and modulation become listed in specifications it will be necessary to see the display in person. Some manufacturers promote “flicker free” monitors in their range (BenQ, Acer for example) which are designed to not use PWM at all and instead use a Direct Current (DC) method of backlight dimming. Other manufacturers such as Eizo talk about flicker free backlights but also list a hybrid solution for their backlight dimming, where PWM is used for some of the brightness adjustment range at the lower end. In fact it seems an increasingly common practice for a screen to be PWM free down to a certain point, and then fro PWM to be used to really drive down the minimum luminance from there.

An easy method of measuring the PWM frequency of a backlight would be ideal, and luckily it can be done using only a camera which allows manual control of the shutter speed. This can quickly and easily identify PWM frequencies in the lower range, but may not be suitable for high frequency PWM. It should be able to detect PWM up to at least 500Hz though, but anything above that may look like a solid block, suggesting no use of PWM, when in fact it might be just using a higher frequency. Further more complex methods such as our oscilloscope setup would be needed to validate flicker-free status for definite.

What we are doing with this technique is turning a temporal effect into a spatial one by moving the camera during capture. The only significant source of light during the image capture is the thin line on the display, which is exposed onto consecutive columns on the sensor. If the backlight is flickering, different columns will have different brightness or colour values determined by the backlight at the time it was exposed.

BenQ GW2760HS – W-LED backlight. At all brightness settings the luminance output is a flat line, showing no PWM is being used. This is part of BenQ’s flicker free range.

The oscilloscope graphs can also allow us to examine the behaviour of the luminance output. Above is a typical W-LED backlight dimmed to 0% where PWM is used. You can see the changes between on and off are very steep and sudden, as the LED backlight is able to turn on and off very rapidly. As we’ve already discussed this can lead to potentially more noticeable flicker and associated issues as the changes are more pronounced.

As we said at the beginning, this article is not designed to scare people away from modern LCD displays, rather to help inform people of this potential issue. With the growing popularity in W-LED backlit monitors it does seem to be causing more user complaints than older displays, and this is related to the PWM technique used and ultimately the type of backlight selected. Of course the problems which can potentially be caused by the use of PWM are not seen by everyone, and in fact I expect there are far more people who would never notice any of the symptoms than there are people who do. For those who do suffer from side effects including headaches and eye strain there is an explanation at least.

With the long term and proven success of a technology like Pulse Width Modulation, and the many years of use in CCFL displays we can’t see it being widely changed at any time soon to be honest, even with the popular move to W-LED backlit units. It is still a reliable method for controlling the backlight intensity and therefore offering a range of brightness adjustments which every user would want and need. Those who are concerned about its side effects or who have had problems with previous displays should try and consider the frequency of the PWM in their new display, or perhaps even try and find a screen where it is not used at all in backlight dimming. Some manufacturers are proactively addressing this concern through the use of flicker free backlights, and so options are emerging which do not use PWM.