minimum clock speed needed for lcd tft display free sample

Since the display includes the Ilitek ILI9320 controller, then your interface requirements are much lower, as the microcontroller no longer has to interface directly with the TFT and instead only talks to the controller chip via a simple interface: either SPI, which takes six wires: RS, CS, CLK, MOSI, MISO and RESET. Or you can use an 8080-compatible parallel interface which takes 13 wires: an 8-bit data bus, and RS, CS, WR, RD and RESET. (There are options to use larger data-buses, up to 18 bits, but I don"t recommend that for a low end microcontroller.)

There are two optional interfaces in which the microcontroller generates all of the clock signals (VSYNC, HSYNC and DOTCLK); you don"t want to do that since it would require a high-end controller.

So just about any microcontroller will do, however you need to have enough flash memory to hold whatever static items you want to display; for example if you are going to be displaying text then you will need to allocate arrays to store bitmaps for whatever fonts you will use. Even a small font can take 60KB.

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Low voltage differential signaling (LVDS, also known as OpenLDI) thin-film transistor (TFT) liquid crystal (LCD) displays typically have a specified resolution and minimum required clock frequency to meet desired resolution. Normally, you will find this information listed in the display data sheet and won’t need to perform any calculations.

However, if you do not yet have access to your display data sheet and only know what resolution you want your system to support, you can estimate what clock frequency you need and determine which serializer/deserializer (SerDes) is appropriate for your application.

%Blanking: The blanking period, or the percentage of time when active video is not being displayed. As shown in Figure 1, it is represented horizontally as horizontal pulse width (HPW), horizontal back porch (HBP) and horizontal front porch (HFP). It is also represented vertically as vertical pulse width (VPW), vertical back porch (VBP) and vertical front porch (VFP).

The values for these blanking parameters are listed in display data sheets. The total blanking period varies from 3% to 39%. If your system uses reduced blanking, then you can estimate %Blanking at 10%. If you are not sure what blanking period your system uses, estimate around 20% and above to be conservative.

Frame rate (or refresh rate):the frequency at which consecutive images (frames) are displayed, and is measured in hertz or frames per second (fps). 60Hz is the most common frame rate, but this value can vary from 24Hz to 70Hz.

Throughput is another metric that you can use to determine whether or not a device will support your desired display resolution. The throughput is the effective payload of video data, and is derived from the required pixel clock frequency and color depth of your system, as shown in Equation 2:

Color depth: For a first-generation SerDes like the SN65LVDS93A, color depth is typically 24-bit red-green-blue (RGB) or 18-bit RGB for single pixel in, single pixel out (SISO) applications, and 48-bit RGB or 36-bit RGB for dual pixel in, dual pixel out (DIDO) applications.

The color depth will determine how many LVDS data lanes your display requires. SerDes serialize data at a rate of 7x the pixel clock frequency on each LVDS data lane. If the color depth is 24-bit RGB, then you will need four LVDS data lanes (there are an additional four bits used for control, which brings the total bit count to 28 bits) and can use a SerDes like the SN65LVDS93A. If the color depth is 18-bit RGB, then you will need three LVDS data lanes (there are an additional 3 bits used for control, which brings the total bit count to 21 bits) and can use a SerDes like the SN74LVDS84A or the SN65LVDS93A.

If the color depth is 48-bit RGB, then you will need eight LVDS data lanes (there are an additional 8 bits used for control, which brings the total bit count to 56 bits) and will need to use a device like the DS90C387 or DS90C189-Q1, which can output as many as eight LVDS data lanes.

When calculating the throughput for DIDO applications, you need to calculate the throughput for the odd pixels and even pixels separately and then add them together. For example, for a 48-bit DIDO application, the total required throughput would be 2 x Pixel Clock x 24.

Since the color depth is 24-bit RGB, you will need four LVDS data lanes. The SN65LVDS93A is a good fit for this application, since it has a pixel clock frequency range of 10MHz to 135MHz. Additionally, the maximum throughput for each LVDS data lane on this device is 135 x 7 = 945Mbps. Because this device has four LVDS data lanes, the total maximum throughput is 945 x 4 = 3780Mbps, which is higher than the minimum required throughput.

So the minimum pixel clock frequency to support a 2048 x 1536 resolution display is 208MHz. However, since this is a 48-bit DIDO application, there are actually two clocks: the frequency is split between them. Each clock must have a frequency of at least 104MHz.

Since the color depth is 48-bit RGB, you will need eight LVDS data lanes. The DS90C387 and DS90C187 are a good fit for this application, since they have a pixel clock frequency range of 32.5MHz to 112MHz (the DS90C387) and 25MHz to 105MHz (the DS90C187) for each channel in DIDO applications. Thus, if you don’t have access to the display data sheet yet, you can still estimate the required pixel clock frequency and throughput to support your desired resolution. If the SerDes does not meet these parameters, data on the display may display incorrectly, or not display at all.

It works with TFT displays available from AliExpress, and I"ve included four examples showing how you can do things that wouldn"t be possible without the ability to read from the display.

You can use an exclusive-OR drawing mode that changes the state of pixels reversibly. Drawing the same thing a second time restores the display to its previous state. This is especially important for dynamic data plotting.

You can write games that perform collision detection by reading from the screen. For example, you could make a pinball game in which the ball bounces off whatever you have drawn on the screen.

To implement these applications without the ability to read pixels from the display would require you to keep a mirror of the display in RAM, and update the mirror every time you draw to the actual display. This would slow down graphics and require a lot of memory: for example, to mirror a 320x240 colour display would require 153.6Kbytes of RAM. To put this in context, the ATtiny414 used to run these examples only has 256 bytes of RAM.

Unfortunately this feature does not work with Adafruit displays, which is why I didn"t include it in my original Tiny TFT Graphics Library 2. It is, however, compatible with all displays based on the ST7735 and ST7789 driver chips available from vendors such as AliExpress and Banggood. Here"s a list of displays I"ve tested:

Adafruit have a range of great TFT displays, in a wide selection of sizes and resolutions, but unfortunately they are not compatible with this library. The reason is that their displays all include a unidirectional on-board logic-level converter to allow them to be used with either 3.3V or 5V, but this has the downside of preventing them from being able to read back from the display memory.

The solution would be to replace the unidirectional logic-level converter on the MOSI connection to the display driver with a bidirectional one, which would require one N-MOSFET and two resistors. I originally planned to include details of how to modify an Adafruit display to implement this, but I"ve decided against this because the displays are fragile, and the risk of ending up with a non-functional display is too great.

This first uses the display commands CASET and RASET to set the column range and row range to the current point. It then gives the RAM read command, RAMRD.

The sequence to shift the 21 bits into the variable pixel needs to be slightly different depending on whether the display uses the ST7735 or ST7789 driver chip. The two if statements determine this from the width of the display, and toggle the sck pin either before or after reading the mosi pin, as appropriate. It took a bit of experimentation to figure this out.

These examples included with the library demonstrate applications of reading back from the display memory. For convenience I"ve used my Universal TFT Display Backpack to run these examples, but that"s not necessary.

This simple demo takes a triangular section of an existing image on the screen, and reflects it through horizontal, vertical, and diagonal lines to create a symmetrical image, like a kaleidoscope. It works best on square displays; here it is on a 240x240 1.54" display:

To run it first draw an image, and then run Kaleidoscope(). For this example the initial image is the Waterfall() demo, used for the title image in the article Tiny TFT Graphics Library 2:

The stopwatch takes advantage of exclusive-OR plotting to draw and undraw the hand when it moves without corrupting the clock face. It is designed for a 128x128 display:

Anything drawn in red on the display is treated as a barrier, and the ball will bounce off it. Any other colours, such as the white text, are ignored and can be used to create an interesting background.

The final demo draws the BarChart() demo, and it then calls BMPSave() to save it to a BMP-format image file on an SD card. Here"s the BarChart() demo running on a 320x170 display:

Here is the version of the Tiny TFT Graphics Library with the extensions for reading from the display, and the demos described above (excluding BMPSave()): Tiny TFT Graphics Library with Read.

7th August 2022: I"ve updated the library to add support for the classic ATtiny processors, such as the ATtiny85; the previous version only worked on the new 0-series, 1-series, and 2-series ATtiny processors, such as the ATtiny402. I"ve also added a photograph of a demo running on the ATtiny85.

I will use a 3.3v 500mA power supply connected to a lipo battery, probably with or maybe without a over discharge circuit. The power supply MIC5219-3.3V have a ENable pin, so if I utilize it, I can get less than 5 micro amps of current draw, which is certainly an overkill, if I use the power on/off thing that cut off 3.3v on the teensy, I can get less than 200 micro amps. I wonder if I can hook a GPIO pin to the power on/off pin, so I can pull it to high or low for a few seconds to turn if off, and also a physical button is connected to the power on/off so I can power it on with one click and hold button to force shutdown.

The linear power supply is [+]Efficient and [+]Small but [-]Can"t output 5v [-]Low max current output [-]Have 500mV dropout voltage @500mA so the battery is unusable when it is 3.7 volts, which is real bad as lithium batteries" protector boards over discharge kicks in @2.4v. I also need 5v for the USB host port for keyboards and mouse. Because the host port is not needed at all times, so I wanted to use existing power bank circuit that auto turns on when peripherals are connected. (Existing circuits are great, maybe efficient and safer), so no boosting required if not needed.

Using the power bank circuit that my li polymer battery comes with (power bank comes with) can [+]output more current, so can also power keyboard mice and hubs. [+]safe, with protection [+]only powers on when there is current draw (Teensy itself may not be able to keep it on, maybe can with the LCD backlight) or/and USB device is connected. Some people add resisters to add current draw, and that is bullshit. Another problem is how to control whether I want the converter to start or not, and have no complete control sucks.

Let us start with the basics first; refresh the knowledge about TN and LCD displays in general, later we will talk about TFTs (Thin Film Transistors), how they differ from regular monochrome LCD displays. Then we will go on to the ghosting effect, so we will not only discuss the technology behind the construction of the TFT, but also some phenomena, like the ghosting effect, or grayscale inversion, that are important to understand when using an LCD TFT display.

Next, we will look at different technologies of the TFT LCD displays like TN, IPS, VA, and of course about transmissive and transflective LCD displays, because TFT displays also can be transmissive and transflective. In the last part we will talk about backlight.

Let us start with a short review of the most basic liquid crystal cell, which is the TN (twisted nematic) display. On the picture above, we can see that the light can be transmit through the cell or blocked by the liquid crystal cell using voltage. If you want to learn more about monochrome LCD displays and the basics of LCD displays, follow this link.

What is a TFT LCD display and how it is different from a monochrome LCD display? TFT is called an active display. Active, means we have one or more transistors in every cell, in every pixel and in every subpixel. TFT stands for Thin Film Transistor, transistors that are very small and very thin and are built into the pixel, so they are not somewhere outside in a controller, but they are in the pixel itself. For example, in a 55-inch TV set, the TFT display contains millions of transistors in the pixels. We do not see them, because they are very small and hidden, if we zoom in, however, we can see them in every corner of each pixel, like on the picture below.

On the picture above we can see subpixels, that are basic RGB (Red, Green, Blue) colors and a black part, with the transistors and electronic circuits. We just need to know that we have pixels, and subpixels, and each subpixel has transistors. This makes the display active, and thus is called  the TFT display. TFT displays are usually color displays, but there are also monochrome TFT displays, that are active, and have transistors, but have no colors. The colors in the TFT LCD display are typically added by color filters on each subpixel. Usually the filters are RGB, but we also have RGBW (Red, Green, Blue, White) LCD displays with added subpixels without the filter (White) to make the display brighter.

Going a little bit deeper, into the TFT cell, there is a part inside well known to us from the monochrome LCD display Riverdi University lecture. We have a cell, liquid crystal, polarizers, an ITO (Indium Tin Oxide) layer for the electrodes, and additionally an electronic circuit. Usually, the electronic circuit consists of one transistor and some capacitors to sustain the pixel state when we switch the pixel OFF and ON. In a TFT LCD display the pixels are much more complicated because apart from building the liquid crystal part, we also need to build an electronic part.

That is why TFT LCD display technologies are very expensive to manufacture. If you are familiar with electronics, you know that the transistor is a kind of switch, and it allows us to switch the pixel ON and OFF. Because it is built into the pixel itself, it can be done very quickly and be very well controlled. We can control the exact state of every pixel not only the ON and OFF states, but also all the states in between. We can switch the light of the cells ON and OFF in several steps. Usually for TFT LCD displays it will be 8-bit steps per color, so we have 256 steps of brightness for every color, and every subpixel. Because we have three subpixels, we have a 24-bit color range, that means over 16 million combinations, we can, at least theoretically, show on our TFT LCD display over 16 million distinct colors using RGB pixels.

Now that we know how the TFT LCD display works, we can now learn some practical things one of which is LCD TFT ghosting. We know how the image is created, but what happens when we have the image on the screen for a prolonged time, and how to prevent it. In LCD displays we have something called LCD ghosting. We do not see it very often, but in some displays this phenomenon still exists.

If some elements of the picture i.e., your company logo is in the same place of the screen for a long period of time, for couple of weeks, months or a year, the crystals will memorize the state and later, when we change the image, we may see some ghosting of those elements. It really depends on many conditions like temperature and even the screen image that we display on the screen for longer periods of time. When you build your application, you can use some techniques to avoid it, like very rapid contrast change and of course to avoid the positioning the same image in the same position for a longer time.

You may have seen this phenomenon already as it is common in every display technology, and even companies like Apple put information on their websites, that users may encounter this phenomenon and how to fix it. It is called image ghosting or image persistence, and even Retina displays are not free of it.

Another issue present in TFT displays, especially TN LCD displays, is grayscale inversion. This is a phenomenon that changes the colors of the screen according to the viewing angle, and it is only one-sided. When buying a TFT LCD display, first we need to check what kind of technology it is. If it is an IPS display, like the Riverdi IPS display line, then we do not need to worry about the grayscale inversion because all the viewing angles will be the same and all of them will be very high, like 80, 85, or 89 degrees. But if you buy a more common or older display technology type, like the TN (twisted nematic) display, you need to think where it will be used, because one viewing angle will be out. It may be sometimes confusing, and you need to be careful as most factories define viewing direction of the screen and mistake this with the greyscale inversion side.

On the picture above, you can see further explanation of the grayscale inversion from Wikipedia. It says that some early panels and also nowadays TN displays, have grayscale inversion not necessary up-down, but it can be any angle, you need to check in the datasheet. The reason technologies like IPS (In-Plane Switching), used in the latest Riverdi displays, or VA, were developed, was to avoid this phenomenon. Also, we do not want to brag, but the Wikipedia definition references our website.

We know already that TN (twisted nematic) displays, suffer from grayscale inversion, which means the display has one viewing side, where the image color suddenly changes. It is tricky, and you need to be careful. On the picture above there is a part of the LCD TFT specification of a TN (twisted nematic) display, that has grayscale inversion, and if we go to this table, we can see the viewing angles. They are defined at 70, 70, 60 and 70 degrees, that is the maximum viewing angle, at which the user can see the image. Normally we may think that 70 degrees is better, so we will choose left and right side to be 70 degrees, and then up and down, and if we do not know the grayscale inversion phenomena, we may put our user on the bottom side which is also 70 degrees. The viewing direction will be then like a 6 o’clock direction, so we call it a 6 o’clock display. But you need to be careful! Looking at the specification, we can see that this display was defined as a 12 o’clock display, so it is best for it to be seen from a 12 o’clock direction. But we can find that the 12 o’clock has a lower viewing angle – 60 degrees. What does it mean? It means that on this side there will be no grayscale inversion. If we go to 40, 50, 60 degrees and even a little bit more, probably we will still see the image properly. Maybe with lower contrast, but the colors will not change. If we go from the bottom, from a 6 o’clock direction where we have the grayscale inversion, after 70 degrees or lower we will see a sudden color change, and of course this is something we want to avoid.

To summarize, when you buy older technology like TN and displays, which are still very popular, and Riverdi is selling them as well, you need to be careful where you put your display. If it is a handheld device, you will see the display from the bottom, but if you put it on a wall, you will see the display from the top, so you need to define it during the design phase, because later it is usually impossible or expensive to change the direction.

We will talk now about the other TFT technologies, that allow us to have wider viewing angles and more vivid colors. The most basic technology for monochrome and TFT LCD displays is twisted nematic (TN). As we already know, this kind of displays have a problem with grayscale inversion. On one side we have a higher retardation and will not get a clear image. That is why we have other technologies like VA (Vertical Alignment), where the liquid crystal is differently organized, and another variation of the TFT technology – IPS which is In-Plane Switching. The VA and IPS LCD displays do not have a problem with the viewing angles, you can see a clear image from all sides.

Nowadays all TV sets, tablets and of course mobile phones are IPS or VA. You can turn them around and see the image clear from all sides. But, for monitor applications the TN technology is still widely used, because the monitor usually is in front of you and most of the time you look directly at it, from top, left or right side, but very rarely from the bottom, so the grayscale inversion viewing angle can be placed there. This technology still is very practical because it is affordable and has some advantages for gamers because it is very fast.

Apart from the different organization of the liquid crystals, we also organize subpixels a little bit differently in a VA and IPS LCD displays. When we look closer at the TN display, we will just see the subpixels with color filters. If we look at the VA or IPS display they will have subpixels of subpixels. The subpixels are divided into smaller parts. In this way we can achieve even wider viewing angles and better colors for the user, but of course, it is more complicated and more expensive to do.

The picture above presents the TN display and grayscale inversion. For IPS or VA technology there is no such effect. The picture will be the same from all the sides we look so these technologies are popular where we need wide viewing angles, and TN is popular where we don’t need that, like in monitors. Other advantages of IPS LCD displays are they give accurate colors, and wide viewing angles. What is also important in practice, in our projects, is that the IPS LCD displays are less susceptible to mechanical force. When we apply mechanical force to the screen, and have an optically bonded touch screen, we push the display as well as squeeze the cells. When we have a TN display, every push on the cell changes the image suddenly, with the IPS LCD displays with in-plane switching, different liquid crystals organization, this effect is lesser. It is not completely removed but it is much less distinct. That is another reason IPS displays are very popular for smartphones, tablets, when we have the touchscreens usually optically bonded.

If we wanted to talk about disadvantages, there is a question mark over it, as some of them may be true, some of them do not rely on real cases, what kind of display, what kind of technology is it. Sometimes the IPS displays can have higher power consumption than others, in many cases however, not. They can be more expensive, but not necessarily. The new IPS panels can cost like TN panels, but IPS panels definitely have a longer response time. Again, it is not a rule, you can make IPS panels that are very fast, faster than TN panels, but if you want the fastest possible display, probably the TN panel will be the fastest. That is why the TN technology is still popular on the gaming market. Of course, you can find a lot of discussions on the internet, which technology is better, but it really depends on what you want to achieve.

Now, let us look at the backlight types. As we see here, on the picture above, we have four distinct types of backlight possible. The most common, 95 or 99 per cent of the TFT LCD displays on the market are the transmissive LCD display type, where we need the backlight from the back. If you remember from our Monochrome LCD Displays lecture, for transmissive LCD displays you need the backlight to be always on. If you switch the backlight off, you will not see anything. The same as for monochrome LCD displays, but less popular for TFT displays, we have the transflective LCD display type. They are not popular because usually for transflective TFT displays, the colors lack in brightness, and the displays are not very practical to use. You can see the screen, but the application is limited. Some transflective LCD displays are used by military, in applications where power consumption is paramount; where you can switch the backlight off and you agree to have lower image quality but still see the image. Power consumption and saving energy is most important in some kind of applications and you can use transflective LCD displays there. The reflective type of LCD displays are almost never used in TFT. There is one technology called Low Power Reflective Displays (LPRD) that is used in TFT but it is not popular. Lastly, we have a variation of reflective displays with frontlight, where we add frontlight to the reflective display and have the image even without external light.

Just a few words about Low Power Reflective Displays (LPRD). This kind of display uses environmental light, ambient light to reflect, and produce some colors. The colors are not perfect, not perfectly clear, but this technology is becoming increasingly popular because it allows to have color displays in battery powered applications. For example, a smartwatch would be a case for that technology, or an electrical bike or scooter, where we can not only have a standard monochrome LCD display but also a TFT LCD color display without the backlight; we can see the image even in

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strong sunlight and not need backlight at all. So, this kind of TFL LCD display technology is getting more and more popular when we have outdoor LCD displays and need a low power consumption.

On the picture above, we have some examples of how transmissive and reflective LCD displays work in the sunlight. If we have a simple image, like a black and white pattern, then on a transmissive LCD display, even with 1000 candela brightness, the image probably will be lower quality than for a reflective LCD display; if we have sunlight, we have very strong light reflections on the surface of the screen. We have talked about contrast in more detail in the lecture Sunlight Readable Displays. So, reflective LCD displays are a better solution for outdoor applications than transmissive LCD displays, where you need a really strong backlight, 1000 candela or more, to be really seen outdoors.

To show you how the backlight of LCD displays is built, we took the picture above. You can see the edge backlight there, where we have LEDs here on the small PCB on the edge, and we have a diffuser that distributes the light to the whole surface of LCD screen.

In addition to the backlight, we have something that is called a frontlight. It is similar to backlight, it also uses the LEDs to put the light into it, but the frontlight needs to be transparent as we have the display behind. On the example on the picture above we can see an e-paper display. The e-paper display is also a TFT display variation, but it is not LCD (liquid crystal), it is a different technology, but the back of the display is the same and it is reflective. The example you see is the Kindle 4 eBook reader. It uses an e-paper display and a frontlight as well, so you can read eBooks even during the night.

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Let us start with the basics first; refresh the knowledge about TN and LCD displays in general, later we will talk about TFTs (Thin Film Transistors), how they differ from regular monochrome LCD displays. Then we will go on to the ghosting effect, so we will not only discuss the technology behind the construction of the TFT, but also some phenomena, like the ghosting effect, or grayscale inversion, that are important to understand when using an LCD TFT display.

Next, we will look at different technologies of the TFT LCD displays like TN, IPS, VA, and of course about transmissive and transflective LCD displays, because TFT displays also can be transmissive and transflective. In the last part we will talk about backlight.

Let us start with a short review of the most basic liquid crystal cell, which is the TN (twisted nematic) display. On the picture above, we can see that the light can be transmit through the cell or blocked by the liquid crystal cell using voltage. If you want to learn more about monochrome LCD displays and the basics of LCD displays, follow this link.

What is a TFT LCD display and how it is different from a monochrome LCD display? TFT is called an active display. Active, means we have one or more transistors in every cell, in every pixel and in every subpixel. TFT stands for Thin Film Transistor, transistors that are very small and very thin and are built into the pixel, so they are not somewhere outside in a controller, but they are in the pixel itself. For example, in a 55-inch TV set, the TFT display contains millions of transistors in the pixels. We do not see them, because they are very small and hidden, if we zoom in, however, we can see them in every corner of each pixel, like on the picture below.

On the picture above we can see subpixels, that are basic RGB (Red, Green, Blue) colors and a black part, with the transistors and electronic circuits. We just need to know that we have pixels, and subpixels, and each subpixel has transistors. This makes the display active, and thus is called  the TFT display. TFT displays are usually color displays, but there are also monochrome TFT displays, that are active, and have transistors, but have no colors. The colors in the TFT LCD display are typically added by color filters on each subpixel. Usually the filters are RGB, but we also have RGBW (Red, Green, Blue, White) LCD displays with added subpixels without the filter (White) to make the display brighter.

Going a little bit deeper, into the TFT cell, there is a part inside well known to us from the monochrome LCD display Riverdi University lecture. We have a cell, liquid crystal, polarizers, an ITO (Indium Tin Oxide) layer for the electrodes, and additionally an electronic circuit. Usually, the electronic circuit consists of one transistor and some capacitors to sustain the pixel state when we switch the pixel OFF and ON. In a TFT LCD display the pixels are much more complicated because apart from building the liquid crystal part, we also need to build an electronic part.

That is why TFT LCD display technologies are very expensive to manufacture. If you are familiar with electronics, you know that the transistor is a kind of switch, and it allows us to switch the pixel ON and OFF. Because it is built into the pixel itself, it can be done very quickly and be very well controlled. We can control the exact state of every pixel not only the ON and OFF states, but also all the states in between. We can switch the light of the cells ON and OFF in several steps. Usually for TFT LCD displays it will be 8-bit steps per color, so we have 256 steps of brightness for every color, and every subpixel. Because we have three subpixels, we have a 24-bit color range, that means over 16 million combinations, we can, at least theoretically, show on our TFT LCD display over 16 million distinct colors using RGB pixels.

Now that we know how the TFT LCD display works, we can now learn some practical things one of which is LCD TFT ghosting. We know how the image is created, but what happens when we have the image on the screen for a prolonged time, and how to prevent it. In LCD displays we have something called LCD ghosting. We do not see it very often, but in some displays this phenomenon still exists.

If some elements of the picture i.e., your company logo is in the same place of the screen for a long period of time, for couple of weeks, months or a year, the crystals will memorize the state and later, when we change the image, we may see some ghosting of those elements. It really depends on many conditions like temperature and even the screen image that we display on the screen for longer periods of time. When you build your application, you can use some techniques to avoid it, like very rapid contrast change and of course to avoid the positioning the same image in the same position for a longer time.

You may have seen this phenomenon already as it is common in every display technology, and even companies like Apple put information on their websites, that users may encounter this phenomenon and how to fix it. It is called image ghosting or image persistence, and even Retina displays are not free of it.

Another issue present in TFT displays, especially TN LCD displays, is grayscale inversion. This is a phenomenon that changes the colors of the screen according to the viewing angle, and it is only one-sided. When buying a TFT LCD display, first we need to check what kind of technology it is. If it is an IPS display, like the Riverdi IPS display line, then we do not need to worry about the grayscale inversion because all the viewing angles will be the same and all of them will be very high, like 80, 85, or 89 degrees. But if you buy a more common or older display technology type, like the TN (twisted nematic) display, you need to think where it will be used, because one viewing angle will be out. It may be sometimes confusing, and you need to be careful as most factories define viewing direction of the screen and mistake this with the greyscale inversion side.

On the picture above, you can see further explanation of the grayscale inversion from Wikipedia. It says that some early panels and also nowadays TN displays, have grayscale inversion not necessary up-down, but it can be any angle, you need to check in the datasheet. The reason technologies like IPS (In-Plane Switching), used in the latest Riverdi displays, or VA, were developed, was to avoid this phenomenon. Also, we do not want to brag, but the Wikipedia definition references our website.

We know already that TN (twisted nematic) displays, suffer from grayscale inversion, which means the display has one viewing side, where the image color suddenly changes. It is tricky, and you need to be careful. On the picture above there is a part of the LCD TFT specification of a TN (twisted nematic) display, that has grayscale inversion, and if we go to this table, we can see the viewing angles. They are defined at 70, 70, 60 and 70 degrees, that is the maximum viewing angle, at which the user can see the image. Normally we may think that 70 degrees is better, so we will choose left and right side to be 70 degrees, and then up and down, and if we do not know the grayscale inversion phenomena, we may put our user on the bottom side which is also 70 degrees. The viewing direction will be then like a 6 o’clock direction, so we call it a 6 o’clock display. But you need to be careful! Looking at the specification, we can see that this display was defined as a 12 o’clock display, so it is best for it to be seen from a 12 o’clock direction. But we can find that the 12 o’clock has a lower viewing angle – 60 degrees. What does it mean? It means that on this side there will be no grayscale inversion. If we go to 40, 50, 60 degrees and even a little bit more, probably we will still see the image properly. Maybe with lower contrast, but the colors will not change. If we go from the bottom, from a 6 o’clock direction where we have the grayscale inversion, after 70 degrees or lower we will see a sudden color change, and of course this is something we want to avoid.

To summarize, when you buy older technology like TN and displays, which are still very popular, and Riverdi is selling them as well, you need to be careful where you put your display. If it is a handheld device, you will see the display from the bottom, but if you put it on a wall, you will see the display from the top, so you need to define it during the design phase, because later it is usually impossible or expensive to change the direction.

We will talk now about the other TFT technologies, that allow us to have wider viewing angles and more vivid colors. The most basic technology for monochrome and TFT LCD displays is twisted nematic (TN). As we already know, this kind of displays have a problem with grayscale inversion. On one side we have a higher retardation and will not get a clear image. That is why we have other technologies like VA (Vertical Alignment), where the liquid crystal is differently organized, and another variation of the TFT technology – IPS which is In-Plane Switching. The VA and IPS LCD displays do not have a problem with the viewing angles, you can see a clear image from all sides.

Nowadays all TV sets, tablets and of course mobile phones are IPS or VA. You can turn them around and see the image clear from all sides. But, for monitor applications the TN technology is still widely used, because the monitor usually is in front of you and most of the time you look directly at it, from top, left or right side, but very rarely from the bottom, so the grayscale inversion viewing angle can be placed there. This technology still is very practical because it is affordable and has some advantages for gamers because it is very fast.

Apart from the different organization of the liquid crystals, we also organize subpixels a little bit differently in a VA and IPS LCD displays. When we look closer at the TN display, we will just see the subpixels with color filters. If we look at the VA or IPS display they will have subpixels of subpixels. The subpixels are divided into smaller parts. In this way we can achieve even wider viewing angles and better colors for the user, but of course, it is more complicated and more expensive to do.

The picture above presents the TN display and grayscale inversion. For IPS or VA technology there is no such effect. The picture will be the same from all the sides we look so these technologies are popular where we need wide viewing angles, and TN is popular where we don’t need that, like in monitors. Other advantages of IPS LCD displays are they give accurate colors, and wide viewing angles. What is also important in practice, in our projects, is that the IPS LCD displays are less susceptible to mechanical force. When we apply mechanical force to the screen, and have an optically bonded touch screen, we push the display as well as squeeze the cells. When we have a TN display, every push on the cell changes the image suddenly, with the IPS LCD displays with in-plane switching, different liquid crystals organization, this effect is lesser. It is not completely removed but it is much less distinct. That is another reason IPS displays are very popular for smartphones, tablets, when we have the touchscreens usually optically bonded.

If we wanted to talk about disadvantages, there is a question mark over it, as some of them may be true, some of them do not rely on real cases, what kind of display, what kind of technology is it. Sometimes the IPS displays can have higher power consumption than others, in many cases however, not. They can be more expensive, but not necessarily. The new IPS panels can cost like TN panels, but IPS panels definitely have a longer response time. Again, it is not a rule, you can make IPS panels that are very fast, faster than TN panels, but if you want the fastest possible display, probably the TN panel will be the fastest. That is why the TN technology is still popular on the gaming market. Of course, you can find a lot of discussions on the internet, which technology is better, but it really depends on what you want to achieve.

Now, let us look at the backlight types. As we see here, on the picture above, we have four distinct types of backlight possible. The most common, 95 or 99 per cent of the TFT LCD displays on the market are the transmissive LCD display type, where we need the backlight from the back. If you remember from our Monochrome LCD Displays lecture, for transmissive LCD displays you need the backlight to be always on. If you switch the backlight off, you will not see anything. The same as for monochrome LCD displays, but less popular for TFT displays, we have the transflective LCD display type. They are not popular because usually for transflective TFT displays, the colors lack in brightness, and the displays are not very practical to use. You can see the screen, but the application is limited. Some transflective LCD displays are used by military, in applications where power consumption is paramount; where you can switch the backlight off and you agree to have lower image quality but still see the image. Power consumption and saving energy is most important in some kind of applications and you can use transflective LCD displays there. The reflective type of LCD displays are almost never used in TFT. There is one technology called Low Power Reflective Displays (LPRD) that is used in TFT but it is not popular. Lastly, we have a variation of reflective displays with frontlight, where we add frontlight to the reflective display and have the image even without external light.

Just a few words about Low Power Reflective Displays (LPRD). This kind of display uses environmental light, ambient light to reflect, and produce some colors. The colors are not perfect, not perfectly clear, but this technology is becoming increasingly popular because it allows to have color displays in battery powered applications. For example, a smartwatch would be a case for that technology, or an electrical bike or scooter, where we can not only have a standard monochrome LCD display but also a TFT LCD color display without the backlight; we can see the image even in

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strong sunlight and not need backlight at all. So, this kind of TFL LCD display technology is getting more and more popular when we have outdoor LCD displays and need a low power consumption.

On the picture above, we have some examples of how transmissive and reflective LCD displays work in the sunlight. If we have a simple image, like a black and white pattern, then on a transmissive LCD display, even with 1000 candela brightness, the image probably will be lower quality than for a reflective LCD display; if we have sunlight, we have very strong light reflections on the surface of the screen. We have talked about contrast in more detail in the lecture Sunlight Readable Displays. So, reflective LCD displays are a better solution for outdoor applications than transmissive LCD displays, where you need a really strong backlight, 1000 candela or more, to be really seen outdoors.

To show you how the backlight of LCD displays is built, we took the picture above. You can see the edge backlight there, where we have LEDs here on the small PCB on the edge, and we have a diffuser that distributes the light to the whole surface of LCD screen.

In addition to the backlight, we have something that is called a frontlight. It is similar to backlight, it also uses the LEDs to put the light into it, but the frontlight needs to be transparent as we have the display behind. On the example on the picture above we can see an e-paper display. The e-paper display is also a TFT display variation, but it is not LCD (liquid crystal), it is a different technology, but the back of the display is the same and it is reflective. The example you see is the Kindle 4 eBook reader. It uses an e-paper display and a frontlight as well, so you can read eBooks even during the night.

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//#define ILI9488_DRIVER // WARNING: Do not connect ILI9488 display SDO to MISO if other devices share the SPI bus (TFT SDO does NOT tristate when CS is high)

This 3.5" EVE TFT bundle has everything you need to get started with this powerful display. The development kit consists of a 3.5" display mounted on an EVE2 graphically accelerated PCA, a Seeeduino, an EVE breakout board, jumper wires, USB cable and 6-inch ribbon cable.

With a resistive touch screen, full color, and a 6 o"clock viewing angle the display is a great way to offer a full user experience. For more information about the display, including its detailed datasheet, check out the 320x240 3.5" Touch Screen Color TFT page.

The EVE chip really makes this TFT module really shine. EVE (embedded video engine) is a cool new technology from FTDI/Bridgetek that simplifies the process of displaying videos and text in an embedded project. All display, touch sensing, backlight, and audio features are controlled by the FTDI FT810 EVE which appears to host the MCU as a memory-mapped SPI device. The host MCU sends commands and data over the SPI protocol. The module can support both SPI and Quad-SPI.

Display technology has moved forward at light speed. For years, even sophisticated equipment made do with numeric and alphanumeric display technology, buttons, and LEDs.

With mass production, manufacturing refinements, and competition, thin film transistor (TFT) displays have drastically dropped in price while dramatically improving in performance. They are the de facto standard to the point where it is not only expected, it is demanded that any modern user interface be full color, brightly backlit, touch sensitive, and have high video speeds and a good viewing angle.

While simple low-cost 8-bit microcontrollers could easily handle the multiplexed 7- and 14-segment LED and alphanumeric LCD displays, the memory, processor speeds, and peripheral resources needed to drive a TFT are more than most modest microcontrollers can handle. As a result, dedicated controller chips, embedded modules, or faster, denser, and more streamlined processor architectures are needed.

This article looks at the factors that make a good MCU-to-TFT interface. This includes memory depths and architectures, paging, data transfer, signaling levels, interfaces, and on-chip peripherals to look for when selecting a microcontroller for a TFT application. It examines the TFT technology and present day product offerings, which your designs will need to drive. It also looks at some microcontrollers that provide native support for color TFT displays, looking at their techniques, features, trade-offs, and limitations. All displays, microcontrollers, drivers, inverters, and development tools mentioned in this article are available from Digi-Key Corporation.

TFT displays are a type of liquid crystal display in which the transistor controlling the pixel’s crystal is etched into a layer of amorphous silicon deposited on the glass (see Figure 1). As in an IC process, very small transistors are geometrically formed. The small size of the transistor means it will not significantly attenuate the light passing through.

The advantage of TFTs is that they are fast enough for video, provide a large and smooth color palette, and are pixel addressable through an electronic two-dimensional control matrix (see Figure 2). Most low-cost displays use an amorphous silicon crystal layer deposited onto the glass through a plasma-enhanced chemical vapor deposition.

Figure 2: Electronically, a stable VCOM reference is used throughout the display, and the gamma corrected drive voltage passes through each transistor.

Many versions of TFT technologies have led us to the modern displays. Early complaints like poor viewing angles, poor contrast, and poor backlighting have been addressed. Better light sources, diffusers, and polarizers make many displays very vivid, some even claiming to be daylight readable. Modern day techniques like in-plane switching improve viewing angles by making the crystals move in a parallel direction to the display plane instead of vertically. Better speeds and contrasts of modern display make them high performance for a fairly low cost.

Since TFTs are not emissive devices, they require backlighting. The most commonly deployed backlight technology is cold cathode florescent lighting (CCFL). These devices were designed, chosen, and used because they are very efficient and have very long lives. Typically, a CCFL bulb is rated as having in the ball park of a 50,000 hour ‘half-life. ’ This means that after 50,000 hours, it still works, but with half the intensity when it was new.

Modern displays, especially the smaller ones, have transitioned to white LED-based backlights. These are easier to manufacture, do not require the high voltage inverter which CCFL bulbs need, and are approaching a lower cost point compared to CCFL technology. Both CCFL and LED technologies will use diffuser layers inside the stackup to evenly distribute light. LED-based backlights may actually be side lights and use a lightpipe structure to distribute the light.

Transflective technology is steadily improving and is available in some TFT displays. This is where both a backlight and ambient external light are used to make the display visible. Sunlight may make it viewable, but generally speaking the transflective displays are less transmissive. This means that the backlight will have to be brighter (and require more power) to be on par with a purely transmissive display that requires a backlight all the time.

With TFT and most color display technologies, an individual pixel contains a red, a green, and a blue picture element (pel). The relative intensity of each color will determine the resulting blended color.

The relationship between the transmittance of light through a pixel and the applied voltage to liquid crystal pels is not linear. This means a standard linear DAC output will not match up with the standard RGB calibrations of standard monitors. In some applications, such as gaming and cell phones, this may not be important, since viewers of low resolution, washed out-video will hardly notice a slight shift in color. But for medical, instrumentation, and other more demanding types of applications, the gamma correction may be an important factor to consider when planning a design.

Either a gamma correction chip or a lookup table can be inserted into the data stream to do this correction. You should have a consistency of the LCD. Note that many LCD manufacturers do not make their own mother-glass. As such, they are subject to the slight variations from supplier to supplier. Unless you use a supplier that truly manufactures its own glass, this could be an issue later on down the road.

The color depth or color palette is dependent on the bit resolution used for each color. This typically ranges from an 18-bit interface consisting of 6 bits each for red, green and blue, to 24-bit interfaces using 8 bits per color.

Some displays will use dithering and alternating pixel colors to achieve a better blend of intermediate colors. Higher frame rates are also used since the persistence effect of phosphor-based displays does not carry over to LCDs. Determine the quality and smoothness of the display you will use. Not every frame rate control technique yields flicker- and jitter-free performance, especially at some resolutions. If you notice it, so will your customers and end users of your design.

The memory required to map the display image is key. While some micros will contain enough memory to hold a single page of display data (and not much else), you can see that a lot of memory is required for even a modest ¼ VGA display. This is more than what a typical microcontroller can house (see Table 1). As a result, an external bus interface to external RAM (SRAM, DRAM, or SDRAM) will be needed, especially if paging will be used.

Table 1: The memory required to map to a display is proportional to three times the square of the resolution because of the three color elements of each pixel.

Paging will allow better display quality since one page can be displayed while the next is being built in the background, then made live. This eliminates ghosting and image flicker when graphics are changing rapidly in effects like scrolling, moving sprites (graphical objects), color shade blending (for overlapping graphics as they move), etc.

A key feature when selecting a microcontroller for TFT interfacing is the DMA support. Multi-channel, flexible DMA will make a world of difference, especially when it comes to moving data between pages, character generator and rendering tables, animations and video. Along these lines, a preprogrammed and autonomous DMA functionality will allow you to refresh a display while the core microcontroller goes to sleep. This is a key power-reducing feature that can make a world of difference when operating from batteries.

Very high volume applications may justify using an OEM only for the glass and implementing your own control electronics from the glass up. This is especially true when designing a very small form factor device where the added flexibility of using your own PCB layout is critical to success. For those designing from the glass up, the primary interface will be drivers for the thin film transistors. The stable common voltage reference to which all pixels are referenced is key. This is called VCOM and several discrete and integrated solutions for generating a VCOM signal are available.

One effective solution is to use the National Semiconductor LMH6640MF/NOPB which is a rail-to-rail (up to 16 volts), voltage feedback, high output (up to 100 ma) amplifier optimized for TFT transistor driving. The fast 170 V/µS slew rate yields a 28 MHz full power bandwidth (at five volts) and its small SOT-23 package can be fit into tight spaces (see Figure 3).

The larger the panel, the more current will be required to operate the transistors. For larger panels, another contender is the Maxim MAX9550EZK+T which can drive up to 800 ma peaks up to 20 volts. It settles to within 0.1 percent in less than 2 µSec and features a soft start circuit to limit inrush current during startup. Note, the VCOM level is usually set between the upper voltage level and ground instead of being set to ground. This allows full scale alternating polarity to be driven to the pixels without the need for a negative power supply.

Also , the VCOM function and all its subtleties are often times integrated into more encompassing TFT driver chips like Texas Instruments’ LM8207MT/NOPB which combines an 18 channel gamma corrected driver with VCOM referencing buffer (see Figure 4). Note that the built-in VCOM buffer will allow a buffer tree to be created from a single reference for larger displays.

One approach to driving a TFT display without the need for a higher end processor is to use a discrete TFT controller chip that can be interfaced to a processor of lesser horsepower. An example is the Intersil TW8811-LD2-GR TFT controller chip (see Figure 5).

Aimed at a specific market segment, in this case automotive applications, the TW8811 combines control and even video standard (analog, RGB, S-Video, NTSC, PAL, and Secam) integration into a single chip controller. It supports and ties together different video sources to allow the same display to be used for navigation systems, engine displays, environmental control, in-car entertainment systems, backup cameras, etc.

The on-chip SDRAM interface provides the depth and cost-effective performance needed for displays up to WXGA resolutions, and the –40 to +85 degree temperature range makes this usable for a variety of harsh environment applications.

If a single microcontroller can control the task at hand as well as the embedded display, this is usually the most cost-effective solution. Most people will use a TFT module which already houses the VCOM, gamma correction, and TFT transistor drivers. As a result, the interface to the module is TTL, CMOS, or Low Voltage Differential Signaling (LVDS).

Thankfully, to help make TFT design tasks doable in a reasonable amount of time, the chip makers provide solutions targeted at display designs. Typically, these are higher-end, 32-bit, RISC-type processor architectures with streamlined peripherals and resources that handle both display-oriented and non-display-oriented functions such as communications, sensor interfacing, etc.

For example, the NXP Semiconductor LPC2478FBD208,551 is an ARM7™-based 72 MHz high- end microcontroller with LCD control up to 1024 x 768, 24-bit pixel resolutions. In addition to the very flexible DMA functionality, it incorporates USB, four UARTS, I²S, RTC, SD/MMC memory card, Ethernet, I²C, CAN, and more. It is a “Swiss Army Knife” processor that targets integrated, single processor type designs.

Devices like this need development environments and evaluation units and NXP is right there. The DK-57VTS-LPC2478 is a programmer’s development system that includes a 5.7 inch TFT with touch interface as well (see Figure 6). Note the 2M x 32 SDRAM for page buffering and graphic manipulations. NXP also offers the DK-57TS-LPC2478 which aims at sensor-based applications.

NXP Semiconductors is not alone by any means. Renesas Electronics America also provides processors with built-in support for TFTs. Take for example the DF2378RVFQ34V, an H8-based processor with advanced block transfer functionality built into the DMA. Like the NXP parts, it incorporates a slew of peripherals, Flash, memory interfaces, and I/O.

Not every processor needs to have a dedicated TFT interface to make it a viable candidate. For example, the TI TMS470R1B1MPGEA is a RISC-based 60 MHz ARM7 processor that can easily interface to a slew of TFT modules that are driven via a digital interface. While some modules need constant refreshing, others can be loaded with display data and generate all the timing and display data movement internally unburdening the host CPU. The CPU must be fast enough to keep up with any animations or video if this is the case.

TI also provides the very high-end Digital Media System-on-Chip (DMSoC) solutions like the DSP-based TMS320DM6446AZWTA. This is not your run-of-the-mill processor. Running at 513 MHz and housing 160 Kbytes of RAM, this 361-pin LFBGA device is part of the company’s high-end DaVinci™ series and is supported by several development platforms, one of them being the TMDSVDP6437 digital video EVM.

Many displays are readily available as test vehicles. Many of these can be directly driven with the processors mentioned here. Many other processors can also be used, like offerings from Atmel (AT91SAM9261B-CU) and STMicroelectronics (STM32F107VBT6).

No matter how many data sheets you read, what it boils down to is this: a display is a visual device. What will ultimately make the decision is how it looks when you display your screens on it.

Disclaimer: The opinions, beliefs, and viewpoints expressed by the various authors and/or forum participants on this website do not necessarily reflect the opinions, beliefs, and viewpoints of Digi-Key Electronics or official policies of Digi-Key Electronics.

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The content is intended to be updated from time to time, I will add more details if I found new display or library update. You can also help me enrich the content by leaving comments below.

You can run various IoT projects prefectly without any display. But not all IoT project only feed data in single direction (IoT to server), some IoT also gather real time information from the server for displaying.

My previous instructables, ESP32 Photo Clock is am example, it download a current minute photo from the Internet, decode the JPEG photo and display it.

There are various real time information in your server or Internet, such as all rooms temperature in your home, server CPU usage, weather forecast, news, stock price, your downloading file is done, your Youtube channel views :>

Many Arduino projects use monochrome display, one of the reason is the limited resources of a MCU. 320 pixels width, 240 pixels height and 8 bits color for each RGB color channel means 230 KB for each full screen picture. But normal Arduino (ATmega328) only have 32 KB flash and it is time consuming (over a second) to read data from SD card and draw it to the color display.

ESP32 have changed the game! It have much faster processing power (16 MHz vs 240 MHz dual core), much more RAM (2 KB vs over 200 KB) and much more flash (32 KB vs 4 MB), so it is capable to utilize more color and higher resolution image for displaying. At the same time it is capable to do some RAM hungry process such as Animated GIF, JPEG or PNG file decoding, it is a very important feature for displaying information gathered from the internet.

Color display have many type of interfaces: Serial Peripheral Interface (SPI), 6-bit, 8-bit, 16-bit, 18-bit and 24-bit parallel interfaces and also NeoPixel!

SPI dominate the hobby electronics market, most likely because of fewer wire required to connect. Most display in my drawer onl