tft lcd with led backlight free sample

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In market, LCD means passive matrix LCDs which increase TN (Twisted Nematic), STN (Super Twisted Nematic), or FSTN (Film Compensated STN) LCD Displays. It is a kind of earliest and lowest cost display technology.

LCD screens are still found in the market of low cost watches, calculators, clocks, utility meters etc. because of its advantages of low cost, fast response time (speed), wide temperature range,  low power consumption, sunlight readable with transflective or reflective polarizers etc.  Most of them are monochrome LCD display and belong to passive-matrix LCDs.

TFT LCDs have capacitors and transistors. These are the two elements that play a key part in ensuring that the TFT display monitor functions by using a very small amount of energy without running out of operation.

Normally, we say TFT LCD panels or TFT screens, we mean they are TN (Twisted Nematic) Type TFT displays or TN panels, or TN screen technology. TFT is active-matrix LCDs, it is a kind of LCD technologies.

TFT has wider viewing angles, better contrast ratio than TN displays. TFT display technologies have been widely used for computer monitors, laptops, medical monitors, industrial monitors, ATM, point of sales etc.

Actually, IPS technology is a kind of TFT display with thin film transistors for individual pixels. But IPS displays have superior high contrast, wide viewing angle, color reproduction, image quality etc. IPS screens have been found in high-end applications, like Apple iPhones, iPads, Samsung mobile phones, more expensive LCD monitors etc.

Both TFT LCD displays and IPS LCD displays are active matrix displays, neither of them can produce color, there is a layer of RGB (red, green, blue) color filter in each LCD pixels to make LCD showing colors. If you use a magnifier to see your monitor, you will see RGB color. With switch on/off and different level of brightness RGB, we can get many colors.

Neither of them can’t release color themselves, they have relied on extra light source in order to display. LED backlights are usually be together with them in the display modules as the light sources. Besides, both TFT screens and IPS screens are transmissive, it will need more power or more expensive than passive matrix LCD screens to be seen under sunlight.  IPS screens transmittance is lower than TFT screens, more power is needed for IPS LCD display.

FocusLCDs.com sent me a free sample of a 4x3” TFT LCD (P/N: E43RG34827LW2M300-R) to try out. This is a color active matrix TFT (Thin Film Transistor) LCD (liquid crystal display) that uses amorphous silicon TFT as a switching device. This model is composed of a Transmissive type TFT-LCD Panel, driver circuit, backlight unit. The resolution of a 4.3” TFT-LCD contains 480x272 pixels, and can display up to 16.7M colors.

For this project, you would need the RA8875 driver board (available at AdaFruit for US$35) to interface the TFT display to the Arduino. It comes with a header which you can solder on as needed.

TFT LCD image retention we also call it "Burn-in". In CRT displays, this caused the phosphorus to be worn and the patterns to be burnt in to the display. But the term "burn in" is a bit misleading in LCD screen. There is no actual burning or heat involved. When you meet TFT LCD burn in problem, how do you solve it?

When driving the TFT LCD display pixels Continously, the slightly unbalanced AC will attract free ions to the pixels internal surface. Those ions act like an addition DC with the AC driving voltage.

Those burn-in fixers, screen fixer software may help. Once the Image Retention happened on a TFT, it may easy to appear again. So we need to take preventive actions to avoid burn in reappearing.

For normal white TFT LCD, white area presenting minimal drive, black area presenting maximum drive. Free ions inside the TFT may are attracted towards the black area (maximum drive area)

LCD displays don’t emit light by themselves. They need a light source, and LED backlights are now dominating the market. In this article, Orient Display’s Bill Cheung provides a complete overview of LED backlight technology, discussing different types, driver technologies, color deviation, brightness options and more.

LCD (liquid crystal display) has long been the dominant technology in the display world. Certainly, there are some emerging competing display technologies—such as OLED (Organic Light Emitting Diode) [1] and micro-LED—that have the potential to threaten LCD’s position in the market. But both are currently only used for niche and high-end markets.

An LCD display can’t emit light by itself. In order to have an LCD display [2] used in a dim environment, a backlight has to be used as the light source. There are a few different technologies that are able to produce backlight ranging from EL (electroluminescent), CCFL (cold cathode fluorescent lamps) and LED (light emitting diode). However, a breakthrough in blue LED technology by Shuji Nakamura [3] led to LED backlights dominating the market.

One of the greatest benefits of LED backlighting is its long lifetime. Normally, LED lifetime can be measured with half-life when the original brightness decreases by 50%. With different LED chip manufacturing materials, technologies and environment used, the LED life can vary from 20,000 hours to well over 100,000 hours.

LED backlights have low power consumption and produce much less heat than other backlight technologies, which extends the durability and performance of the other display components. Furthermore, this reduces the risk of fire and explosion. LED backlights are also driven with DC (direct current) and low voltage (can be as low as 1.5V), which are good for battery drive and emit no interference to the circuitry. With the development of LED technology, the LED chips become small. So, it is possible to produce very thin backlight (0.5mm thick or thinner).

Although white LED is the most popular color, LED backlight can be made into different single colors, bi-colors and tri-colors [4] (Figure 1) (Figure 2). With RGB LED backlight color mixing, normal 8 color LED backlight can be produced (Figure 3).

LED backlight can be classified as bottom (array) lit and side (edge) lit backlights, and each have their plusses and minuses. The advantages of the bottom lit (array) backlight are that it is uniform and bright. Its disadvantage is high current draw, thickness, heat dissipation and cost. Meanwhile, the advantages of the side lit backlight are its thinness, flexibility in design, low current and lower cost. The main disadvantage of the side lit backlight is its non-uniformity—hot spots can be seen from most of the side lit backlight from certain angle. Figure 4 compares the bottom lit and side (edge) lit backlight LCD types.

Now let’s look at LED backlight structures. An LED backlight can be simplified into layers starting with a LED chip, light guide, diffusor and reflector (Figure 5). This is the lowest cost structure. Except for some very low current efficiency LCD displays—such as utility meters, battery-powered clock, watch, GPS and so on—most LCD displays need backlights to be visible in the dim lighting. Most often the backlight is actually at the back of the LCD. In rare cases, this light can be done as front light. The traditional LCD structure with LED backlight shown in Figure 6.

Direct current driving: This is the simple and low-cost way to drive a LED backlight, however, be mindful of the current limit otherwise the LED life can deteriorate quickly. The solution is simply to add a current limiting resistor in the circuit. Current limitation resistors value calculation formula: R = (V0– Vf)/If.Also be mindful of reverse drive, otherwise, the LED chip can break down easily.

LED driver with constant current: The advantage of constant current LED driver is that it will be the best option to use when building your own fixture or working with high powered LED because they avoid violating the maximum current specified for the LEDs, therefore avoiding burnout/thermal runaway. They are easier for designers to control applications, and help create a more consistent bright light.

LED driver with constant voltage: Using a constant voltage LED driver makes sense when using an LED or array that has been specified to take a certain voltage. This is helpful because constant voltage is a much more familiar technology for design and installation engineers. Moreover, the cost of these systems can be lower, especially in larger scale applications.

There are a variety of ways to connect a backlight and LCD module electrically. It can be done with wires that are soldered on the LCD or LCD module. It can be connected using pins, which can be soldered onto the LCD or LCD module. A third way is to use a FPC (flexible printed circuit), which can be soldered or plugged in a ZIF (zero insertion force) connector. And finally, there is the connector method. With this method you use connectors which can be plugged into mating connectors.

As the LED is manufactured via the semiconductor process, there are some color deviations that can be a quality control issue. One way to solve the issue is through a process of selection and sorting after manufacturing the LEDs. The LEDs are sorted into different categories or bins. How this sorting is done and what each bin actually contains is defined differently by each LED manufacturer. The backlight manufacturer can choose from which bin they take the LEDs for backlight color hue.

Some customers might request very fine binning by the LED manufacturer, which can be very expensive since only a very small percentage of the LEDs manufactured would meet the requirements for a specific bin. Figure 7 shows an example of the bin selection from Nichia, the most renowned LED manufacturer in the world. Figure 8 shows the 1931 CIE chromaticity diagram. And Figure 9 shows the color deviations (bin definition) by Cree for a qualified production lot.

In actual LED backlight production, most customers will accept the LED color for two big categories: white with yellowish (warm) and white with bluish (cold). Of course, the LED brightness will also need to be defined. For general application, most customers will accept a brightness tolerance of 70 percent.

It is extremely hard to estimate the LED backlight lifetime or MTBF (mean time between failures) because there are so many variable factors. However, the most important is the temperature on the LED chip. The factors that can affect the LED chip temperature include: surrounding temperature, humidity, driving current, voltage, backlight design (how many LED chips to be used, how close to each other, heatsink design), backlight manufacturing process (type and thickness of adhesive), quality of the LED chip and so forth.

To test the LED life is also very time consuming, requiring at least 1,000 hours. That’s the reason why no LED manufacturers can guarantee LED backlight life and most backlight manufacturers also are reluctant to provide lifespan data. As for LCD manufacturers, they need to discuss it with the customer to understand the applications and provide suggestions. It is normal that the LCD datasheet lists the typical life time and avoids providing a minimum lifetime. From Figure 10, we can see that over room temperature, the current needs to decrease as the temperature increases. At over 85°C, the LED is not usable.

To estimate LED backlight lifetime, you can use ballpark estimation or theoretical calculation. Let’s first examine the ballpark method. To take white LED as example, the nominal biasing current is 20mA. If we use a safe lifetime estimation, we can estimate using Table 1.

Now let’s use the theoretical calculation approach. As we previously mentioned, LED life is affected by a lot of factors: surrounding temperature, humidity, driving current, voltage, backlight design (how many LED chips to be used, how close to each other, heatsink designed), backlight manufacturing process (type and thickness of adhesive), quality of the LED chip and so on. LED chip manufacturers are not willing to give absolute values of LED chip lifetimes, but there is a theoretical calculation that we can use.

Temperature is the determination factor for LED chip life, while LED chip manufacturers use LED junction temperature to predict LED chip life more accurately. An example is:

Finally, let’s look at ways to increase LED backlight brightness. There are many ways to increase LED backlight brightness, but all these measures are balanced with performance and cost. Here are some of the methods:

For the LCD module side, using better aperture opening ratio, anti-reflection coating on surface, optical bonding. This results in higher cost. Actually, this measure is not to increase LED backlight brightness directly but to increase to the visibility to users.

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Bill Cheung is an engineering lead and marketing manager at Orient Display, an LCD and display technology provider with over two decades of industry experience in delivering cutting edge display solutions. You can browse Orient Display"s knowledge base [7] to learn more about LCDs.

Focus Displays offers a wide range of standard full color TFT displays. 64 million unique colors, high brightness, sharp contrast, -30C operating temperature, and fast response time are all good descriptions of a TFT display. This is why TFT technology is one of the most popular choices for a new product.

Thin Film Transistor (TFT) display technology can be seen in products such as laptop computers, cell phones, tablets, digital cameras, and many other products that require color. TFT’s are active matrix displays which offers exceptional viewing experiences especially when compared to other passive matrix technologies. The clarity on TFT displays is outstanding; and they possess a longer half-life than some types of OLEDs and range in sizes from less than an inch to over 15 inches.

Cold-Cathode Fluorescent Lamp (CCFL) is an AC driven backlight that requires an inverter to convert DC to AC. The AC signal and inverter may generate EMI (Electromagnetic interference) and arcing; Arcing must be eliminated for Intrinsically Safe products.

CCFL’s are still available, but are becoming a legacy (obsolete) component. TFT displays equipped with a CCFL require higher MOQs (Minimum Order Quantities) than displays with LED backlights.

Red, Green and Blue (RGB) backlights are built with either a single LED that produces red, green and blue colors or with three separate Red, Green or Blue LEDs.

RGB backlights require a controller to regulate the different intensities of each color. The controller’s function is to combine unique levels of Red, Green and Blue to produce any of 64M different colors.

Backlight brightness (Luminance) is measured in nits. A nit being the amount of light that one candle delivers in a 1 square meter box. The intensity of the LED backlight can be critical when operating in low light or in direct sun light and is usually controlled by adjusting the DC voltage. In many applications this is accomplished through pulse-width modulation (PWM)

The majority of TFT displays contain a touch panel, or touch screen. The touch panel is a touch-sensitive transparent overlay mounted on the front of the display glass. Allowing for interaction between the user and the LCD display.

Some touch panels require an independent driver IC; which can be included in the TFT display module or placed on the customer’s Printed Circuit Board (PCB). Touch screens make use of coordinate systems to locate where the user touched the screen.

Resistive touch panels are the lowest cost option and are standard equipment on many TFT modules. They are more common on smaller TFT displays, but can still be incorporated on larger modules.

Resistive touch panels are constructed using flexible materials with an air gap between and are coated with a resistive layer. When an object applies pressure to the top layer, it makes contact with microdots located on the bottom layer. This allows the touch screen to find the location of the touch using X and Y coordinates.

Custom resistive touch screens are an option if the customer requires a seal or gasket to be in contact with the glass and not in contact with the touch panel.

Capacitive touch panels have become popular with such software as Windows 8®, Android® and Apple®. Additionally it is used in products such as cell phones and tablets, where multi-touch and zoom capabilities are important.

Contrast ratio, or static contrast ratio, is one way to measure the sharpness of the TFT LCD display. This ratio is the difference between the darkest black and the brightest white the display is able to produce. The higher the number on the left, the sharper the image. A typical contrast ratio for TFT may be 300:1. This number ratio means that the white is 300 times brighter than the black.

TFT LCD displays are measured in inches; this is the measurement of the diagonal distance across the glass. Common TFT sizes include: 1.77”, 2.4”, 2.8”, 3”, 4.3”, 5”, 5.7”, 5.8”, 7”, 10.2”, 12.1 and 15”.

TFT resolution is the number of dots or pixels the display contains. It is measured by the number of dots along the horizontal (X axis) and the dots along the vertical (Y axis).

Certain combinations of width and height are standardized and typically given a name and a letter representation that is descriptive of its dimensions. Popular names given to the TFT LCD displays resolution include:

Transmissive displays must have the backlight on at all times to read the display, but are not the best option in direct sunlight unless the backlight is 750 Nits or higher. A majority of TFT displays are Transmissive, but they will require more power to operate with a brighter backlight.

Transflective displays are readable with the backlight off provided there is enough ambient light. Transflective displays are more expensive than Transmissive also there may be a larger MOQ for Transflective. However, Transflective displays are the best option for direct sunlight.

A primary job of the driver is to refresh each pixel. In passive TFT displays, the pixel is refreshed and then allowed to slowly fade (aka decay) until refreshed again. The higher the refresh frequency, the sharper the displays contrast.

The controller does just what its name suggest. It controls the drivers. There is only one controller per display no matter how many drivers. A complex graphic display with several thousand pixels will contain one controller and several drivers.

The TFT display (minus touch screen/backlight) alone will contain one controller/driver combination. These are built into the display so the design engineer does not need to locate the correct hardware.

If you do not see a Thin Film Transistor (TFT) Display module that meets your specifications, or you need a replacement TFT, we can build a custom TFT displays to meet your requirements. Custom TFTs require a one-time tooling fee and may require higher MOQs.

Ready to order samples for your TFT design? Contact one of our US-based technical support people today concerning your design requirements. Note: We can provide smaller quantities for samples and prototyping.

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.