Computer Components

Lcd Cover

Selecting a TFT LCD monitor their embedded applications

I've been amazed at the amount of electronic gadgets with small and medium-sized TFT color LCD screens, which are in the market. Looking back on last weekend's trip, I remembered a friends cell phone to organize the trip, no LCD screen on the phone. Then I run, I used the GPS to get there, is the second LCD screen. Then travel moments were caught on my digital camera, a second LCD screen. Coming home, I downloaded the photos onto a digital picture frame in the living room, a second LCD screen. The small size LCD monitors are everywhere! I looked around the house and wondered what else could use a small LCD screen? A quick glance at, and I came up with - the thermostat, security system, stereo, lights, control panel (see Figure 1 mm), remote control, running on a treadmill, washing machine, car instrumentation, .. and the list goes on and on. Most importantly, such interactions, the LCD display can help to improve end-user experience is an advantage.

Previously, not so many products could afford to feature color LCD screen, but the price has come down dramatically in recent years to drive economies of scale and competition between the shows producers. Since the embedded application designer, you might consider using a color LCD display to the next product design. There are many things to understand, so that the planning decisions, major steps are:

- Choosing a color TFT LCD display project

- Choosing a microcontroller and interact with the screen

- Drawing of something, but the display driver development

- Save some time by using the existing tools, Graphics Library, development platforms

In this first post, I cover the topic selection of the color TFT LCD display aspects of the user experience. Like any other specialized field, the display market has its own terms and terminologies. So, to get that out of the way so we can all speak the same language. When talking to the screen manufacturer, you may hear something like, "This seems to model the color 3.5" QVGA with LED backlight. "

Let's break this sentence down one by one:

Color - Simply mind can think of this as either a "black and white" or "color". But there is more to it than that. We will cover more on this later.

3.5 "- This is simply the size of the screen, which is similar to when you buy a TV. For different sizes. Bigger screen still see from afar, but also more expensive.

QVGA - a reference to the name of the display resolution of 320 × 240 pixels. Similar to a digital camera because the screen, a larger number of pixels is shown in more detail in the picture.

LED backlight - Without a light source behind, you can not see any TFT LCD monitor

I will now cover each of the four factors above for more information.

Color Depth:

Subject color depth seems trivial at first and how it is. But I'd like to spend time explaining the details, because it has a significant impact on the microcontroller interface and display, and also the firmware. Monochrome display has only two states for each pixel on and off, and just requires a certain amount of memory per pixel. When the more colors you want more bits per pixel required to represent the color of that pixel. If you are using 2 bits per pixel (BPP), so each pixel can display 4 different colors. Generally low number of bits per pixel, the display supports only shades of gray colors.
The shift away from black, white and gray, we enter the kingdom of the RGB colors. What is RGB you may ask. In short, the RGB color model is to represent each color intensity values ​​of the prime colors of red, green and blue. Wikipedia has a detailed explanation of the RGB and I do not try to reinvent the wheel here. Starting read more about RGB. Do not pay attention to the section "Digital representations."

Market, the display of some sellers is simply that the display is an RGB display. This is good enough to recognize that the display supports colors, in the sense that you and I look forward to. Some also specify either the 65K, 262K or 16.8 million colors, it may be true that man's eyes are probably not sufficient to differentiate all these different colors, and the screen is not enough to display all the pixels of different colors can be made in one view, but knowing that the evidence supports either 65K, 262K or 16.8 million colors, is still an important application of the designer.

If the display supports 65K colors, it means that each pixel represents a 16-bit value, the RGB model is 565, which represents Red 5-bit, 6-bit green, and blue 5-bit. Therefore, to represent each pixel, 2 bytes of memory is needed.

If the display supports 262K colors, it means that each pixel represents a 18-bit value, the RGB model is 666 It may be difficult to represent the 18-bit memory from 2 bytes and 2 bits are needed per pixel.

If the display supports 16.8 million colors, it means that each pixel represents a 24-bit value, the RGB model is 888, and 3 bytes of memory is needed per pixel.

Without going into too much detail yet, it is clear that the colors have an impact on memory usage, is often called (image) frame buffer. I will cover this more when other basics are explained.

Screen size and resolution:

Most of us are familiar with the concept of screen size and resolution to buy a computer monitor. My laptop screen size is 15 inches measured diagonally resolution of 1400 x 1050 pixels, this resolution is also known for SXGA +. I do not remember all the names, specific pixel, but a decent reference can be found on Wikipedia, http://en.wikipedia.org/wiki/Display_resolution

In embedded systems, screen size and resolution are much smaller. For example, a 320 × 240 pixel screen, which is also known as QVGA (Quarter VGA, which is a VGA 640 × 480). Personally, I think, by using a name reference is dangerous, the actual pixel should always be used when communicating with suppliers, the design team members, customers, virtually all. It is dangerous to use the reference names, because misunderstanding can occur. Ask someone what WQVGA resolution, and you'll probably get different answers from different people at 480 × 272, 480 × 247, 432 × 240, 400 × 234, ... you get the idea that this can be quite confusing.

A certain resolution, you'll find screen sizes to suit application requirements. 320 × 240 display can be found ranging from 2.4 "and 5.7". You really do not find any screen larger than 5.7 "and 320 x 240 resolution, because each pixel is too large and the granularity of each pixel is too coarse to the average end user at this stage. In my experience, does not quite set the screen resolution first, then the whole. It is more iterative process, you can specify a combination that is kind of what you're looking for, then check the market what the out-of-the-shelf parts are available, go back to fine-tune the options and requirements again. Alternatively, you have the opportunity to work with screen manufacturer's own work on display, which would suit you need, tools, and payment is typically what you want is still prepared the current manufacturing process.

Backlight:

Again, wikipedia has a brief article on the backlight, check it out. Most small and medium-sized LCD LCM screens for embedded applications are available in LED or CCFL backlight. What you need to know is that most of the screens that you choose to use LED backlighting. Forward voltage on the LED screen looks different, but it is defined on-screen information. Backlight power supply is typically separated from the operating power supply monitor itself, which can be 3.3V, and / or 5v. In addition, all the RS232 LCD requires a positive and negative drive voltage. Many of the displays have an internal circuit, to simplify the design process. But some are not, and in addition to the external circuit is required, so do not pay attention to that.

Now that you're armed with the understanding of basic terminology, you do not have any problems, when someone says "display I'm using my project is a 3.5-inch display 320 × 240 resolution, supported by at least 16-bit color depth, and LED backlighting. Way to go.
It is still a lot of things have been aware of the selection screen is also touch-screen option, Flat Flex Cable (FFC), the display of the product life cycle how to get samples to work with a supplier, etc. I will cover more of these in part 2 and thematic frame buffer for future post, but until then, browse the some of the distributors' catalogs and see if you can find a display that would work well for your next project. 

About the Author

serial lcd, display lcd module

Can you only replace the glass cover on a MacBook pro, if the LCD is perfectly fine?

I have a macbook pro which i cracked the glass on, the main crack is on the black soured but goes across the screen, however lt is working perfectly fine with no problems, i understand it would be a costly job if i where to have to have the entire screen replace. However i was wondering if it would be possible if apple would only replace the glass screen?

yes take it to the genius bar and explain to them you want the glass replaced.
is it under warranty ? if it is have them do it - usually its like 100 bucks or so.

Replacing a scratched LCD cover on a Canon EOS 5D SLR