Flexible LED Display

Due to the creative customization of flexible LED displays, they are very suitable for immersive experiences with changing shapes, so we can see the unique effects brought by flexible LED displays in many fantasy experience halls.

Flexible LED displays can create various strange shapes. For images that need to be designed and displayed with more complex shapes, flexible LED displays are the best choice.

The LED flexible display screen is mainly composed of LED soft module unit boards. The reason it has a certain bending amplitude characteristic is mainly related to the raw materials of the PCB circuit board used in the product. Conventional LED display unit boards use ordinary PCB circuit boards, which are generally called rigid circuit boards. The intuitive feeling is that it is a rigid board that cannot be bent, similar to rigid plastic.

The flexible LED display uses a PCB circuit board made of a flexible insulating material. Therefore, it not only has bending characteristics but also has stronger dust and heat resistance than ordinary LED displays. As a result, the price will be slightly higher than that of ordinary LED displays.

The PCB circuit board’s thickness used in conventional LED display screens is generally 1mm, 1.2mm, 1.6mm, 2.0mm, etc. In most cases, the thicker the PCB thickness, the more reliable the stability of the LED screen product, as it is a rigid board. Therefore, under normal circumstances, most of the daily shapes seen are squares, rectangles, diamonds, etc. Spherical and cylindrical display screens cannot be realized, and solutions for arc-shaped design LED display applications are rarely used.

However, with the industry’s development in recent years, ordinary LED displays can no longer meet the industry\’s needs. The emergence of special-shaped screen modules has enabled LED advertising screens to achieve various shapes. For a long time, LED special-shaped screens have been realized by traditional rectangular flat module assembly or wrapping, such as common curved and circular screens.

New features of the LED display industry-flexible LED display

It is understood that the many advantages of LED flexible displays are beyond the reach of ordinary curved displays. The connection surface of the LED soft module special-shaped screen is different from that of traditional displays. The traditional PCB board is made of glass fiber material, while the flexible module is equipped with a high-strength, strong magnetic core connection device made of the flexible insulating substrate. FPC circuit boards, masks, and bottom shells are made of high-temperature, bending-resistant silicone materials, with high-strength compression and distortion resistance, which can perfectly solve all kinds of installation difficulties when turning corners and edges.

Most installation methods use magnetic column suction, and the “one-install-ready” installation method is adopted. This means that the shape is customized according to the customer’s needs, and then it can be directly adsorbed to achieve a one-step installation. The magnetic installation method is as simple as the conventional indoor screen installation method, and the cabinet connection lines are all connected by the speed connector, which is firm and reliable.

Today, as products in the industry become increasingly homogenized, most small and medium-sized display companies have to find ways to survive and create unique products. Flexible displays can be shaped arbitrarily because of their good ductility. This is a “weapon” for realizing various creative displays.

Flexible LED displays are usually used in special-shaped display occasions. The entire product includes visual design, structural design, structural construction, and LED display systems. Therefore, when evaluating the price of such products, the cost of the LED display system can be evaluated on the premise of considering the feasibility of the product.

At present, LED flexible display screens are mainly used in science and technology museums, museums, art galleries, and other occasions. Combining the atmosphere of the scene and the special-shaped flexible LED display screens cooperate to create a scientific and technological design. At present, flexible LED display screens still have some technical shortcomings, and it is difficult to deal with the complex outdoor environment. Therefore, the current flexible LED display screens are mainly used indoors and half-indoors.

Without considering the design cost, structure cost, labor cost, frame, and other system accessories. The LED flexible screen can calculate the price from the following aspects

(1) Module spacing

Take P2 and P2.5 as examples to show their prices. Currently, on the market, the price of a P2 flexible LED display is generally 8000-9500RMB/m²; the price of a P2.5 flexible LED display is generally 5000-6500RMB/m², the larger the spacing, the lower the price. The price here is only calculated based on the price of the flexible screen module for the entire screen, excluding the frame, mounting bracket, and other system accessories. And when the market price fluctuates, the overall cost fluctuates greatly.

(2) Module chip brand

Jingtai, National Star, San’an, Jingtai, Xinguangtai, etc. Use different brands, and the price will have a more obvious gap. This is the same as the mobile phones we use in our daily life, which are worth 7000 and 8000, as well as 700 and 800. Module chips of different brands have different workmanship and materials.

(3) Refresh frequency

The refresh frequency is also called the vertical frequency, that is, the vertical scanning frequency of the display. It refers to the number of times the display can display images per second, and the unit is hertz (Hz). The higher the field frequency, the more times the image is refreshed, the smaller the flicker of the image display, and the higher the picture quality.

Note that the so-called “refresh times” here and the “picture frame number (usually expressed in FPS)” that we usually say when describing game speed are two completely different concepts. The latter refers to the scanning frequency of the electron gun of the kinescope displayed by the dynamic image processed by the computer per second.

The lamp beads and chips used by different modules are different, and the refresh rate is also different. The effect displayed by the high refresh rate is better than the effect displayed by the low refresh rate, so the corresponding price of the high refresh rate will be more expensive. Some.

(4) Other expenses

The above three expenses accounted for the most costly, but some other expenses are also not small. For example, the cylindrical screen of a large underground shopping mall was installed by JYLED in Thailand before, from site surveys, and design drawings to construction, and then To the end, it took 5 months before and after. The cost of a worker for a day is as high as 700 RMB a day, which is not a small expense when combined.

The LED flexible screen is a kind of the latest ultra-thin flexible LED screen, including the LED display unit and the signal processing unit, power supply unit and circuit connected to it through the circuit board are all flexible.

With its beautiful embossed lines and various unique shapes, it can give people dynamic beauty under the change of colors.

We often see a lot of cylindrical screens when we go shopping in the mall, as well as some other LED screens of different shapes. The screens are filled with beautiful video content, including the promotion of clothing brands, cosmetics, and Products such as shoes, etc., these video content can easily attract our attention, and let us remember the names of certain brands imperceptibly so that when we buy related products in the mall, we will Unconsciously choose the brand product that I have seen in the LED display. This is why businesses prefer to use LED displays to advertise their products or services and LED cylindrical screens and other LED displays of various shapes are more suitable for decoration in shopping malls, which is also a combination of beautiful designs.

The flexible display screen built for the command center this time has a cylindrical shape, which fits the architectural design of the command center. The cylindrical screen adopts a special design circuit layout PCB multi-layer process design, and the best bending angle is >135°.

Principle of flexible LED display drive circuit

The Design of a Conventional Driving Circuit for an LED Display Screen

The LED display drive circuit is designed to be compatible with the control system and is typically categorized into two modes: dynamic scanning drive and static latch drive. In a dynamic scanning drive, the rows of light-emitting diodes on the display screen share a set of column drive registers and each row\’s lighting time accounts for a fraction of the total time. By leveraging the human eye\’s visual persistence effect, a complete text or image can be seen if the refresh rate is greater than 50 Hz.

The conventional drive circuit uses serial-in and parallel-out general integrated circuit chips for column data latches and low-power NPN transistors for column drives. If a monochrome dot matrix is used, several cascaded integrated circuit chips and line scanning tubes are required. The system sequentially moves and latches data for each row, controlling which LEDs are lit via the corresponding transistor. This process repeats rapidly to form a complete text or image.

The LED display circuit is categorized into two modes: dynamic scanning drive and static latch drive, based on the control system used. In the dynamic scanning drive mode, each row of the light-emitting diodes on the display screen shares a set of column drive registers, and the lighting time of each row is a fraction of the total time. A complete text or image can be seen by using the visual persistence effect of the human eye as long as the refresh rate of each line is greater than 50 Hz.

The conventional drive circuit for a monochrome dot matrix uses serial-in and parallel-out general integrated circuit chips for column data latches and low-power NPN transistors for column drives. The system requires several cascaded integrated circuit chips and line scanning tubes. The data for each row is moved and latched sequentially, controlling which LEDs are lit via the corresponding transistor. This process rapidly repeats to form a complete text or image.

The defects of the conventional drive circuit

Although the design structure of the conventional drive circuit is relatively simple, it has two defects:

(1) When a certain row of row driving tubes is valid, the lighting current of all LEDs corresponding to the row will flow through the row of driving scanning tubes, and the number of LED tubes lit in a row depends on the display. The text or graphics are constantly changing, so the current flowing in the line scanning tube has a large change, which will change the pressure drop of the tube;

(2) The change in current caused by the number of lit L ED tubes will also affect the fluctuation of the power supply voltage value, which will affect the voltage at both ends of the first row of L ED tubes, making it continuous with different display texts or graphics. Fluctuations affect the uniformity of the brightness of the entire display.

Therefore, the author designed a column constant current drive circuit. This method can eliminate the fluctuation of the power supply voltage and the line scan.

The influence of the change of tube pressure drops on the brightness of the LED display screen. Figure 3 shows the relationship between the relative brightness of a light-emitting diode and the current flowing in it. It can be seen from the curve that: within a certain forward current working range, its luminous brightness is approximately proportional to the current flowing in it.

It is a current-driven device. Therefore, as long as the current flowing in each LED light-emitting tube can be guaranteed to be constant, the brightness can be guaranteed to be consistent.

It can be seen from the working principle of the conventional drive circuit that because the row and column drive tubes are all working in a saturated state,

The column constant current drive circuit is shown in Figure 4.

When the power supply voltage VDD is stable, the high-level output voltage V of 74HC595 is also very stable. For example, when the power supply voltage VDD is 6V, V = 5.9V. So when a certain bit of 74HC595 output is high, the L ED of its corresponding column will be lit, and the current flowing in it is approximate:

As long as the values of R 1, R 2, and R 3 are selected reasonably, the current flowing in the LED can be guaranteed to be stable, and the LED light-emitting diode can work in the best state of forward current and corresponding luminous brightness.

With this column\’s constant current driving mode, it can be achieved that no matter how many LED tubes are lit in a row, although the tube voltage drop of the row driving tube still changes, the power supply voltage VCC can also be changed. The current flowing in the LED light-emitting diode is constant, thus ensuring the uniformity of the brightness of the LED display.

5　Concluding remarks

Compared with the original conventional drive circuit, the LED display constant current drive circuit overcomes the shortcomings of the conventional drive circuit with only minor changes and ensures more perfect performance. The author has passed the actual use of multiple displays All have got the ideal display effect.