LED display DIY

1. Door head LED strip screen

The LED strip screen on the door head has strong dynamics and bright colors, which can attract attention. It is mainly used to publish the latest advertising information and is widely used in the door heads of banks, photo studios, beauty salons, mobile phone stores and other stores.

2. Assembly significance

The LED industry chain is already very complete. All accessories can be easily purchased online. The technical parameters of LEDs are becoming more and more unified. The industry standards have basically been formed, and all spare parts have been modularized. This provides material guarantee for self-assembly of LED screens . LED strip screens are long in shape, with high packaging and transportation costs, but relatively low material costs. Local assembly of LED screens has laid a cost advantage. In addition, end users are not familiar with LED screens, which improves the competitiveness of local sales of LED screens. Therefore, self-assembly of LED screens and local sales can obtain the maximum profit.

We take the door head LED control card as an example to describe the assembly process of a F5 128x32 door head LED large strip screen (1 meter long and 0.25 meter high) and the theoretical knowledge involved. The effect diagram is shown in Figure 1:

3 LED strip screen

The composition of LED banner screen is the same as that of small LED strip screen, which is composed of unit board, power supply, control card and connection line. Here we will focus on the difference from small LED strip screen.

3.1 Unit Board

The unit boards commonly used for door head LED strip screens are classified according to brightness, dot pitch, and scanning frequency.

3.2 Brightness

CCD is generally used as the unit of measurement. Since CCD is difficult to measure, the industry also uses the ambient brightness index to measure it. The following are the definitions of each level of brightness:

Indoor brightness: Environments that require fluorescent lighting during the day

Semi-outdoor brightness: No fluorescent lighting is required during the day, the sun cannot directly hit the screen, the screen background is a wall, and the sun is not transparent

Outdoor brightness: The sun shines directly on the screen, and the screen background is open, which can transmit sunlight.

3.3 Dot Pitch

It is the distance between the light points. It mainly depends on the distance of the viewer. The viewing distance of the door head screen is generally within 30 meters, and generally no more than P16 (16mm) is used, and P7.62 is commonly used. The denser the dot pitch, the finer the strokes of the displayed characters, and the more dots, the more expensive the screen per unit area.

3.4 How many minutes and how many scans

In the LED unit board, there are several scanning modes: 1/16, 1/8, 1/4, 1/2, and static. How to distinguish? The simplest way is to count the number of LEDs and 74HC595s in the unit board. See the unit board below (Figure 2). There are 64x32 single red LED lights and 16 74HC595s. (One 6025 is equivalent to two 74HC595s)

Calculation method: Divide the number of LEDs by the number of 74HC595s and then divide by 8: 64 x 32 / 16 / 8 = 16 scans

(Front) Figure 2 (Back)

Look at the unit board below (Figure 3):

Enlarged front and back (Figure 3)

32x16 LED spots, 16 74HC595.

Calculation method: The number of LEDs divided by the number of 74HC595s divided by 8 = 32 x 16 / 16 / 8 = 4 scans

If the same LED light is used, the brightness of 1/16 scan is higher than 1/8, and the static (1/1) brightness is the highest. Indoor screens generally use 1/16 scan, and semi-outdoor screens generally use 1/16 or 1/8. For screens placed in an environment where the screen is often exposed to strong sunlight, it is best to use 1/4 scan.

This time we use the unit board of "Semi-outdoor F5 (P7.62) single light single red 1/16 scan 08 interface" (Figure 2), which has high brightness and low price.

Common problems of unit boards:

Q: Is it true that the higher the screen brightness, the better? How should the screen brightness be determined?

A: No, the higher the screen brightness, the higher the price. Too high brightness will be dazzling and uncomfortable. The brightness of the screen should be determined according to the brightness of the environment. For environments that do not require fluorescent lighting during the day, we recommend using a semi-outdoor 1/16 sweep unit board. If it is a main road, facing west, with no trees around, and it is very bright during the day, use 1/8 sweep.

Q: There are so many specifications for dot pitch, which one is better? The denser the better?

A: No, the denser the better. If it is too sparse, it will be hard to read at a close distance. For banners, 7.62mm is more suitable. Some stores want to save money and make a large banner, so they use a 30mm pitch unit board. However, the road is very narrow, and pedestrians on the opposite side will see that the words are too big, so they have to stop and look carefully to understand the content, which is counterproductive.

3.5 Control Card

Here we recommend the door head LED control card, which is specially designed for door head LED strip screens. It is easy to use, has suitable functions, and has obvious price advantages. Now the LED market competition is fierce, and it can help you effectively reduce costs and improve efficiency. The following introduces the parameters of the control card:

Door head LED large screen control card

(1) Introduction

The card supports 64-dot high LED strips, multi-language support, and can display any font and GIF animation, providing a professional, highly reliable, and low-cost solution for storefront LED screens and banners. It is easy to operate and has rich effects.

(2) Application

16/32 dot indoor and outdoor strip screen, 64 dot indoor strip screen, 64 dot indoor small LED screen

(3) Features

Control points: maximum 1024x32 points two-color, 1/16 scan maximum 1024x64 monochrome, 1024x32 two-color, 512x64 two-color, 1/8 scan maximum 1024x32 monochrome, 512x32 two-color 1/4 scan maximum 512x32 monochrome, 256x32 two-color.

Scanning method: 1/16 1/8 1/4 scan.

Parameter change: sent via serial port, no jumper design.

Display effect: Support various fonts and pictures of any size, GIF animation.

Motion effects: various, GIF animation.

Output interface: 16PIN 08 interface.

Scan control: Hardware, frequency adjustable.

Storage capacity: FLASH 4Mbit, no battery required, can be saved even when power is off. (Can save 256 512x32 monochrome pictures)

Communication method: RS232/RS485/USB.

Supports networking of 250 screens.

Software language: Chinese, English, multi-language support.

Debugging and installation: quick and easy installation and debugging

. Working environment: Temperature -20 to + 80.

3.6 Power supply and power calculation

The power of the LED screen generally depends on the number of 595 units on the unit board. The maximum power of a fully lit 595 is 0.4A.

You can calculate the power by counting the number of 595 on the unit board. If the screen only displays text, the power of 1 595 is within 0.2A. Since the maximum output power of many power supplies is not as large as the nominal power, and it is rare to be fully lit, it is basically OK if the maximum power is equal to the nominal power. Of course, it is better to choose a larger power.

Here we recommend using a 5V LED power supply with an iron shell, with a power range from 5V 10A to 40A.

Tip: How do you know if the power supply is sufficient? When the screen is fully lit, measure the voltage of the power supply terminals, which should be between 5v-4.7v.

3.7 Connection

Since the door head LED screen involves a wide variety of components, the connection between them is more complicated than that of a small strip screen. The following is an introduction to the connection between the components. Due to different scanning methods, there are different interfaces. The most commonly used ones are 08 interface, 12 interface and 04 interface. The different interfaces are mainly different in the arrangement order of the signal lines, but the principle is the same. The control card generally uses 08 interface. When the interface of the unit board is inconsistent with that of the control card, a conversion line needs to be made.

LA=A，LB=B，LC=C，LD=D

ST=LT=LAT=L, CLK=CK=SK=S, OE=EN, N=GND

There are 3 conversion line methods

1. Cut the middle of the finished cable, rearrange the order and connect them, and tie them with electrical tape. (This method is most used)

2. Tear up the cables and rearrange them to make the head.

3. Use a conversion connector. (The simplest method is to add an additional conversion board)

Let's start assembling:

A Check the power supply voltage to see if it is around 5V.

Check the power supply voltage, find out the DC positive and negative connections of the switching power supply, connect the 220V power cord to the switching power supply (after confirming that the connection is correct, connect to the AC or NL terminal) and then plug it in. You will find that a light on the power supply will be on, then use a multimeter, DC gear to measure the voltage between V+ and V-, and make sure the voltage is between 4.8V-5.1V. There is a knob next to it, and you can use a cross screwdriver to adjust the voltage. In order to reduce screen heating and extend life, the voltage can be adjusted to between 4.5V-4.8 in places where the brightness requirement is not high. After confirming that there is no problem with the voltage, disconnect the power supply and continue to assemble other parts.

B Observe the interface between the unit board and the control card

The control card has R1 R2 R3 R4...but the unit board usually only has R1 or (R1 R2). How should I connect them?

R1 on the control card corresponds to the first row of unit boards, R2 corresponds to the second row of unit boards, R3 corresponds to the third row of unit boards, and R4 corresponds to the fourth row of unit boards, see the figure below:

Make a data cable according to the picture below. The blue and red ones are the cables, and the red ones are the parts that need attention. The yellow box is the cable head. It is recommended to use cable pliers.

Production process: (As shown below, finally press with LED-cable pliers)