A small mobile phone based on the Taishan School

I. Project Description
    This project is a small mobile phone project based on the LCSC development board "Taishanpai". The learning content includes: Linux compilation environment setup, SDK compilation, common Linux commands, device tree, screen selection and debugging, screen touch driver, etc.
    The main tasks in this project include designing and soldering a 3.1-inch MIPI screen adapter board, designing and 3D printing the small mobile phone casing. The program currently uses the "default landscape" firmware. After assembly, I will try writing my own program. Based on
    my design of the "3.1 MIPI adapter board" in the training camp, I added "12V PD power supply" and "UART", both of which use Type-C connectors. This increases the distance between the "Taishanpai" and the "adapter board", so the length of the "surface nut post" and "pogo pin" is insufficient and needs to be reselected. At the same time, the casing needs to be redesigned to increase the "thickness" of the phone, and two new "Type-C" interfaces need to be added to the casing.
    Because the length of the pogo pin has a range (before and after spring compression), the length of the surface nut post is determined first, and then the pogo pin is selected. After testing in SW, it was found that the distance between "Taishanpai" and "adapter board" changed from 3mm to 6mm, which is enough to fit the typec socket. Therefore, a 6mm high surface mount nut post was selected on the board, and a 6.5mm high pogo pin was selected on the board (6.5 before compression, 4.5 at the compression limit).
    During the learning process in the training camp, most of the time I watched the live replays and watched each video carefully. Because the original tutorials jump back and forth between multiple links, it is not easy for a beginner to get an overall idea. Therefore, based on the original tutorials, I wrote CSDN according to my own understanding, sorted out the ideas, and "added" the problems I encountered in the learning process. There are some articles with a high degree of completion, the links are as follows:
    (1) Environment setup and SDK compilation
    (2) Common Linux commands
    (3) Linux device tree
    (4) Screen selection and debugging
    (5) Comprehensive project

Note: The above articles are for my own reference in the future and are more applicable to myself.


The official tutorial for Taishanpai is available here. Part

II: Schematic Design
   . This schematic design refers only to the 3.1 MIPI adapter board. Most of the circuitry follows the official tutorial, so the principles will not be explained further; only the general approach will be outlined.
   The wiring sequence of the Taishanpai 3.1 MIPI interface is inconsistent with that of a 3.1-inch screen, so an adapter board is needed to match the wiring sequences.
   Taishanpai itself has a backlight circuit, which is led out through the 3.1 MIPI interface, with a maximum output of 110mA. However, the maximum backlight current that a 3.1-inch MIPI screen can withstand is 25mA. Directly connecting the Taishanpai's backlight circuit to the screen could cause it to overheat or even burn out. Therefore, the 3.1 MIPI adapter board is designed with two backlight paths: one provided by the Taishanpai MIPI connector, and the other by the onboard backlight circuit. These are selected using a 0Ω resistor.
   The 3V3 of the Taishanpai MIPI connector provides power to the onboard backlight circuit, and the PWM signal controls the output voltage of the onboard backlight circuit. TP's I2C is converted to PWM via an I2C-to-PWM chip. Therefore, TP's I2C terminal controls both the touchscreen and the backlight.
   The newly added PD power supply and UART circuit are as follows:
CH224K uses a single resistor configuration; CFG1 is grounded via a 24K resistor, which will induce a 12V voltage.
III. PCB Design:
See notes for the comprehensive project.
IV. Purchase Items List:



Material
Model
Reference Link
:




Taishanpai
2+16
https://lckfb.com/project/detail/lctspi-2g-16g?param=baseInfo
Recommended version: 2+16.


MIPI adapter board
is not
available in this project
; you can directly prototype it and then purchase components according to the BOM, soldering the adapter board. RTC connector without Pogo pins and surface mount nuts are sold separately.


Pogo pins with
a 6.5mm surface mount height are available here
: https://item.taobao.com/item.htm?u=f352jcuff2f2&id=750082995689&spm=a1z09.2.0.0.47fc2e8dDghyEo
6.5mm surface mount


nuts are available here: https://detail.tmall.com/item.htm?u=f352jcuf5bf0&id=675714153951&spm=a1z09.2.0.0.47fc2e8dDghyEo&skuId=5033314679469 31-pin MIPI FPC cable with a 0.3mm surface mount height is also available here
: https://detail.tmall.com/item.htm?u=f352jcuf5bf0&id=675714153951&spm=a1z09.2.0.0.47fc2e8dDghyEo&skuId=5033314679469 Type A, 50mm long, same direction: https://item.taobao.com/item.htm?u=f352jcuf07f9&id=618662306027&spm=a1z09.2.0.0.5d7f2e8dnF3uzf One TP-Link FPC cable, 26 pins, 0.5mm, Type A, 50mm long, same direction: https://item.taobao.com/item.htm?u=f352jcuf69d2&id=555563074622&spm=a1z09.2.0.0.5d7f2e8dnF3uzf One cable , M2x12 screws. https://detail.tmall.com/item.htm?id=616455063246&spm=a1z09.2.0.0.5d7f2e8dnF3uzf&u=f352jcuf57ce No need to buy nuts, at least 3 are required. V. Acknowledgements: Thanks to Engineer Wu, the development team, and the LCSC development board team.