At present, a large number of LED dot matrix screens use the Hub75 interface as shown in the figure below. If you want to drive it, you need to occupy 13 IO pins. Some LED screens with a larger dot matrix need to use 14 pins, that is, the GND of the fourth pin in the right row is changed to signal channel E, as shown in Figure 2. When doing various experiments related to LED dot matrix screens, if you use Dupont wires to connect these pins, it will probably make you dazzled. If you connect them incorrectly or not securely, it will cause even more headaches. So the idea of ​​making an adapter for the ESP32 development board came up. I found a project on Github for ESP32 DevKitC V1 , but now most ESP32 development boards on the market have been upgraded to ESP32 DevKitC V4. V4 has 8 more IO pins than V1. Therefore, I referred to this project to learn PCB drawing board from scratch and made this Hub75 Adapter for ESP32 DevKitC V4.

make

In fact, before I started doing it, I didn't expect that with the development of technology, various online services would have become so perfect. I basically used Lichuang's one-stop service.

• PCB drawing: LCEDA , foreign users can use  EasyEDA accordingly . You can directly draw schematic diagrams, PCB boards, etc. online. All steps can basically be completed directly online (the automatic routing part still requires downloading a client tool. Of course, automatic routing still has some flaws, which will be discussed later). A novice like me who has no foundation at all can get started by simply learning.
• Component procurement: Lichuang Mall
• PCB customization: Jiali Chuang has two opportunities to make boards for 5 yuan a month. The 5 yuan includes 5 samples and shipping, which is almost like free money.

The finished PCB board is shown in the picture below: 

Features

In the process of making this Hub75 adapter board, full consideration was given to future usage scenarios and actual problems encountered, so that it has the following characteristics:

• Easy to plug and unplug : The board has reserved pads according to the IO pins of ESP32 DevKitC V4. You only need to solder 2 rows of 19-pin headers and plug the ESP32 development board directly into the headers. According to actual needs, the Hub75 connection end can be welded with a simple 2X8 IDC connector to be directly connected to the dot matrix module through a flat cable, or directly buckled to the back of the dot matrix module through the 2X8 female header, thereby avoiding the previous dozen lines everywhere. Flying around. As shown in the two pictures below.
  
  
  
• Comes with TF card module : The soldering pad for the TF card slot is reserved on the PCB. If you want to use the TF card to store various pictures that need to be displayed, then it can be used. At the same time, the SPI interface leads to pins. If other SPI devices are needed, they can be easily connected.
  
• Compatible with Hub75E : Lead out the E pin required by Hub75E. You can choose to use a jumper cap to configure it as one of IO0/IO2/IO12 according to your actual situation.
  
• Additional IO pinouts : 3.3V and GND are pinned out, as well as IO1/IO3/IO34/IO35/IO36/IO39 for easy expansion.
  
• Support external power supply : In actual use, perhaps the power supply source does not have a micro USB that can be directly connected to the USB interface of the development board. Then you can use a 5V power cord to supply power directly through the binding post. In order to prevent misoperation, it is also arranged here. A jumper cap allows you to optionally enable external power. Also refer to this article , the capacitor position is reserved to prevent device damage caused by sudden current from the external power supply.
  
• To solve possible timeout errors when deploying the ESP32 development board : According to the introduction here and this project , add optional 10uF capacitors on EN and GND.
  
• With 4 M2 positioning holes : easy to install and fix.

Usage

• In the most streamlined mode, you can only weld 2 sets of 19-pin female headers, and add a 2X8 IDC cable connector according to actual needs, or simply weld a set of 2X8 female headers on the bottom.
• Other components can also be added according to actual conditions.

source code

• The schematic diagram of the project can be found in the src/Schematic directory in my Github library   . If you need to make secondary modifications, you can simply import it into LCEDA or EasyEDA.
• There are Gerber board making files under  src/Gerber  , which can be easily submitted to your favorite board making manufacturer for board making. Of course, I still recommend the service of Jialichuang here. After all, there are two special opportunities for 5 yuan every month, so you don’t have to use it in vain.

test

For the test code, see the source code in the test directory, which is the PlatformIO project. Just configure the screen height and width in platformio.ini according to your actual LED dot matrix screen situation. The test code mainly uses the ESP32 HUB75 MatrixPanel I2S DMA library.