A tablet based on the A133_Allwinner

# Project Description This is a tablet computer based on the Allwinner A133 processor, which can run Android and Linux systems. It is equipped with a 7-inch 1024X600 resolution touch LCD screen and a 3000MAh battery. Built-in dual-band wifi6 Bluetooth 5.2 module, running memory 2GB, built-in 32GEMMC, can be connected to an external TF card, and uses TYPE-C port for power supply. Video link：[https://www.bilibili.com/video/BV1c8411d7L9/](https://www.bilibili.com/video/BV1c8411d7L9/) # Open Source Agreement This project is licensed under the "CC-BY-NC-SA 4.0" Creative Commons license. Please do not use it for commercial purposes. Please indicate the source when reprinting. # Project Properties This project is made public for the first time and is my original project. The project has not won any awards in other competitions. # Project Progress * The project will be initiated on May 14th to determine the needs. * The schematic design was completed on June 21st. * The PCB design was completed on July 3 and sent for proofing. * The PCB was re-modified on July 4th. The 3mil line width cannot be free, so it was changed to 3.5mil and re-routed. Purchase components. * The 3D shell design was completed on July 8th and sent to 3D Monkey for proofing. * The PCB was sent on July 9th, components arrived one after another, and we started soldering the bga. * From July 10th to 14th, the welding failed. I repurchased tools such as DDR and ball-mounting steel mesh. In the end, the DDR test at 888MHz would randomly fail. * On July 15th, I printed the board again at JLC and selected SMT, waiting for express delivery. * The express delivery arrived from July 23rd to 28th, and I was on a business trip. * On July 29, the DDR 888MHz test was successful and the remaining components were soldered. Burn into the android system to test wifi, 3.5 audio interface, usb and other functions. * On August 14th, I drew a back plate to attach copper sheets for heat dissipation, but the effect is unknown. # Project Introduction ## 1.Hardware The PCB is designed according to JLC's free prototyping rules for 4-layer boards, with 3313 lamination, 1.2mm thickness, line width and line spacing 3.5mil, vias 0.3/0.4, and size within 10x10. The components are basically placed on the front to facilitate patch processing, and the back is the FPC connector for the display.   ### 1.1Framework  ### 1.2Structure Considering the cost and the design to adapt to different needs, the shell is divided into three parts: outer frame, middle layer and backplane. The outer frame is made of PLA engineering plastic material, which has high hardness. The middle layer is made of X resin SLA photosensitive resin material with low cost. If the backplane has heat dissipation requirements, aluminum profile CNC can be used, which can be directly attached to the processor and DDR. If you want You can choose PLA or SLA for low cost.  The middle layer buckles on the outer frame as a fixing bracket for the PCB and display. If you feel the buckle is not firm enough, you can choose small screws to continue fixing it. The display screen is directly stuck on the outer frame. The back and surrounding sides can be stuck with double-sided tape. Note that it is difficult to remove after installation. Please make sure there is no problem with the screen before installing it. The purpose of this design is to make the screen flush with the outer frame (it is recommended that the color of the outer frame be black to match the screen).  When installing the PCB, pay attention to the protruding part on the side in the direction of the arrow in the picture. Insert it in one direction first and then use a little elasticity of the outer frame to clamp the other side. The process is a bit difficult, and it is difficult to pull out after installation. It is recommended to install the PCB first. Then install the LCD screen. If you want to facilitate disassembly and assembly, you can make the slot at the interface of the outer frame larger. ### 1.3Wiring Let’s talk a little bit about the wiring design. In order to use the free sample coupons, a 4-layer board design is adopted. The main difficulty lies in the A133 fan-out and DDR routing. The A133 package is a 0.5pitch BGA, and the fan-out has a 3.5mil line width and spacing. For routing, some pads have been changed to oval shapes, and the DDR is as much as 3W, and lamination is free. The closest structure is the 3313 structure. The 50Ω impedance requires a line width of 6.16mil. The one I used has a 4mil impedance deviation. The lamination is signal layer-GND layer-VCC layer-signal layer, and the DDR wiring area is signal-GND-signal-VCC. Pay attention to the high-current voltage traces such as VCC-CPU and VCC-SYS. They should be as`Thick and short`as possible, and more holes should be drilled at the layer-changing connections. Before wiring, it is best to find some official hardware design guide materials and the like, which will help avoid pitfalls and ensure a smooth pass.     ## 2.Software and Testing There is no need to write code in this project, just burn the image file directly and it can be used. The original intention of the design is to make a tablet that can be used normally and can be used to learn Linux. The debugging port and some peripheral GPIOs are connected to the hardware, which can be used to expand module learning. ### 2.1DDR Test After getting the PCB board with some components soldered, you can first perform a DDR test through the DragonHD software, connect to the computer through the USB OTG interface, open DragonHD and select A100&A133_AXP707, LPDDR3 frequency 888, click the start button and then press the reset button on the board. Start testing.  ### 2.2Burn in the Android Image I used the PhoenixCard software to burn the image file into the TF card to start. The built-in EMMC has not been used yet. Insert the TF card into the computer, open PhoenixCard and select the corresponding firmware. First click on the recovery card to format the TF card, then select the startup card and click to burn the card.  ### 2.3Serial Port Viewing Information The Jtag and serial ports are connected to the board, which can be used for debugging and viewing information. The Jtag port is currently unused, and the serial port pins are as shown below:  Set the baud rate to 115200 for communication. The interface uses a 1.27-spacing row due to its size. There is an adapter board designed at the back to convert it to a 2.54-spacing pin for easy debugging and use. Through the serial port information, we can locate the problem. For example, the system failed to start before. By checking the information, I found that the communication with the PMU was not normal. I later found out that the voltage of the PL port was selected to a power supply that defaults to 1.8V at startup. Orally, causing abnormal communication between a133 and axp707.   ## 3.Assembly The flat plate structure is relatively simple and can be installed as follows. 1、First clamp the middle layer on the outer frame, and then fix the PCB board on the middle layer. 2、Connect the FPC cable of the LCD screen, stick the double-sided tape on the back of the LCD screen and buckle it into the outer frame. 3、Connect the battery, speaker, antenna, etc. and secure them. 4、Close the back cover and tighten the screws.  ## 4.Parameter Introduction Tablet performance parameters are as follows: **Dimensions**： 173x109x15mm **Screen**： 7 inches, 1024x600 resolution **Processor**： Allwinner A133 4-core Cortex A53 **Memory**： 2G LPDDR3 **Storage**： 32G EMMC, can be expanded with TF card **Battery **： 3.7V 3000mAH lithium battery **Operating system**： Android 10 **WIFI**： Dual-band WiFi6 **Bluetooth**： BT5.2 **Audio interface**： 3.5mm Headphone interface **Data interface**： USB2.0x1，USB OTGx1 **Charging interface**： Headphone interface ## 5.Use and Others ###### About use It is no different from an ordinary tablet. Press and hold the power button to turn it on and off. At present, the basic functions have been implemented. APK can be installed, and video playback and music playback can be used normally. There is a bug that the speaker will still play when headphones are plugged in. Check the circuit and the headphone plug-in signal can be detected normally. The speaker amplifier chip turns off the IO. If it is pulled low, it may be that the system is not properly matched. In addition, the wifi signal is not good. Maybe the antenna I bought does not match. I used the antenna I used for a 4G mobile phone before. ###### How to Find Information Information about some chips is not easy to find on the Internet. Unlike ST and the like, it can be found through Baidu search. I have compiled several methods here: 1. Log in to the official website directly and search for the corresponding chip model to see if there is any corresponding information. This kind of general chip information can be found, such as MCU, there are user manuals, application manuals, data manuals, etc. But the official websites of companies like Quanzhi have little information.  2. Log in to the relevant forums. You can search to see if the corresponding chip or company has a forum. Log in to see the posts posted by others. Some people will provide some information. For example, [Index \(Home Page\) / WhyCan Forum \(Wow Cool Developer Community\)](https://whycan.com/) , you can download it.  3. Search for relevant projects on platforms such as JLC Open Source Platform. Many project attachments have corresponding information shared.  4. Add relevant QQ groups, search for QQ groups with related projects or names, and after joining, you can find the information you want in the file column.  5. If you really can’t find the ability to use money, go buy a development board. There will definitely be a lot of information given away. And you can use a development board to verify it in the early stage. If you have a lot of money, it is recommended to buy a development board, which can save a lot of time.  ## Conclusion This is my first contact with a Linux project, and I am grateful for the opportunity provided by the JLC open source platform. At the same time, I would like to thank @logicworld for the series of articles " Getting started with ARM high-speed circuit design from scratch " written on the JLC open source platform. I have benefited a lot. The most important thing is to remind you that there is a problem with the DDR schematic encapsulation in the JLC shared library, which avoids mistakes in the first board making. I recommend that friends who want to get started read it. I also bought Wei Dongshan’s Linux development board before, but it just sat there gathering dust. I hope that through this project, I can learn relevant knowledge. If you are interested, you can leave a message. If there are many people, we will open a QQ communication group. I'm a novice about Linux, and I'm willing to work with you to make progress together .