LED-11. Make a very big size 384 X 512 RGB Matrix #2

 In a previous article, I decided to make a large-sized LED signboard to promote the cafe (BlueBird) and even talked about the process of making the frame.

In this article, we will talk about the connection and power of the LED panel, and the connection of the Raspberry Pi.

 

LED Pannel

The LED panel I use is P2.5 128X64. In the figure below, the hole is an M3 standard hole that can fix the panel, and the depth is 5mm.

<P2.5 128 X 64 LED Matrix size>

There are 128X64 = 8192 pixels in one panel. Therefore, since a total of 24 panels are used, a total of 196,608(192K) pixels are used. An LED signboard of this size cannot be controlled by a single Raspberry Pi.

 

First Design

I plan to control the LEDs using a total of 3 Raspberry Pis.


<Configuration>


The following figure shows the connection of the top 9 panels.

<Top 9 pannels connection>

This configuration worked successfully. However, the refresh rate of the screen was around 120Hz.

<Top 9 panel test results>

I want a clean output with a slightly higher refresh rate. Therefore, we decided to reduce the number of LED panels connected per Raspberry Pi.

 

Second Design

 This time I reduced the length of the chain from 3 to 2. Therefore, the refresh rate will rise due to the reduced Daisy connection. And I changed the LED mapping method to VMapper. The daisy connection using a general Hub75 cable is connected horizontally. However, VMapper connects the LED panels in the vertical direction.

<Vertical mapping>

 
options.pixel_mapper_config = "V-mapper"

By changing the configuration in this way, a refresh rate of about 150 Hz can be obtained.


LED Driving HAT(Electrogragon HAT)

I will use Electrodragon's product for controlling the LED panel. For more information about this product, please refer to the following articles. I strongly recommend that you read these articles beforehand.

This product can connect a total of 3 Hub75 cables. And each Hub75 cable can connect multiple LED panels in a daisy connection method.


Jumper Setting for big size pannel

A little work is required to use an LED panel with a height of 64 pixels or more. The pin shape is slightly different depending on the version of Electrogagon's LED HAT product. The figure below shows the jump settings for two types of HAT. Refer to "LED-10. Make 256 X 126 size RGB Matrix" for the article related to Electrogagon's LED HAT product jump setting.


<Jumper setting for driving 128X64 LED matrix>

 

 

Jumper Setting for P3 socket

In the previous articles, I had never even used a P3 socket. But this time, I have to use the P3 socket for a total of 3 Daisy connections. To use the P3 socket, I need to change the jump position in HAT as follows.

<jumper setting for P3 socket>

As the text on the board implies, you can select whether to use the RTC or P3 socket by using a jumper. Since I will be using the P3 socket, of course I will set the jumper towards "EN P3 Chain".


Power

All products used in this project use a 5V power supply. Raspberry Pi, LED panel, and Ethernet hub all use 5V power. Therefore, you only need to prepare 5V SMPS.
Let's calculate the power capacity of SMPS.

 

Required Power Calculation

For Raspberry Pi, 5V 2A is enough. I need 8A(40W) because I will be using a total of 4 Raspberry Pis.
And the Ethernet switch needs up to 0.5A(2.5W).
The LED panel uses an average of 11.7W/pannel and a maximum of 35W/pannel. Therefore, if 24 panels are used, an average of 280.8W(56.2A) and a maximum of 840W(168A) are required.

 Therefore, if you add up all the required power, an average of 323.3W and a maximum of 882.5W are required.

 

Power Supply(SMPS)

 I prepared 4 SMPS of Meanwell's LRS-350-5, SE-450-5 and 5V-26A, 5V-30A.

5V-30A SMPS is used independently for Raspberry Pi power supply. And the remaining 3 SMPS will make one 5V power rail and use it as the LED power source.

LRS-350-5 model can supply rated power of 5V 60A. And SE-450-5 can supply rated power of 5V 75A. Therefore, with 3 SMPs, a total power supply of 805W is possible. 

This value is 91.2% of the maximum value of 882.5W and 249% of the average value of 323.3W. The maximum power of 882.5W is when all LEDs are white, that is, all R, G, and B LEDs are on. I'm not going to make a situation like this, so a power supply of 805W would be good.

 

<Meanwell LRS-350-5, SE-450-5>>


Tips: It is recommended to separate the LED power and Raspberry Pi power. LED signboards fluctuate power consumption as the screen changes. Therefore, the power supply may momentarily become unstable, which may affect the Raspberry Pi. A momentary voltage drop can degrade the Raspberry Pi's performance. In severe cases, a system down may occur.


Terminal block and shortbar

There are many parts that need to be connected to a 5V power supply. LED panel uses one power table per 2 panels. Therefore, a total of 12 power connections are required. In addition, a total of 17 wires up to 4 Raspberry Pis and an Ethernet switch must be connected to a 5V power supply. To make this task easier, a terminal block and a short bar are used as shown below.

<termonal block and shortbar>


Network Switch

The 4 LED players and the LED server will send and receive screens using the network. Therefore, it is better to configure an independent network. And since the screen must be transmitted in real time, a reliable switch must be used. Especially when playing video, a reliable network is even more important because the four players need to be well in sync. Be sure to use a network switch that supports gigabit. 

I used an 8-port gigabit switch from NETGEAR.
At first, I used a cheap 5-port switch, but the screen transmission packet was not delivered properly, so I experienced the phenomenon that the entire electronic display screen was broken. This problem was solved by replacing the switch.

<NETGEAR GS308 gigabit switch>


 Wrapping up

So far, I have looked at the connection of the LED panel installed on the frame, how to use the Raspberry Pi and Electrodragon's LED HAT, and the power calculation. Next, I will talk about software installation and setting for operating the LED signage in earnest.

 

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