4-inch beam splitter prism screen-HDMI driver board

(This project was first published in Hard Innovation Society, and LT's development notes are organized and posted on it. Friends who want secondary development should not miss it. 4-inch square USB capacitive touch HDMI screen - Hard Innovation Society (jlc.com))
 
1. Product Introduction
A 4-inch square HDMI screen, the screen resolution supports 480X480 and 720X720, with HDMI audio function and USB touch function. There are two ways to play, one is as a HDMI screen with touch, the other is to turn on the mirror display, install a 70mm splitter prism on it, and turn it into a cool pseudo-holographic HDMI screen.
 
2. Application scenario
DIY a very small and mini external display screen for computers, mobile phones, etc. to satisfy the fun of DIY.
The display has USB touch function and HDMI audio function, which is more interesting and practical.
Compatible with 70mm splitter prisms on the market, used for DIY pseudo-holographic HDMI screen.
 
3. Product Overview
HDMI screen function:
Based on LT8619C, HDMI to RGB drive LCD screen display image, refresh rate 60Hz.
Onboard HDMI audio circuit, based on IIS audio amplifier CS4344 + APA2068 dual-channel audio amplifier solution, with an 8Ω1W speaker on board.
USB touch function: Based on CH554 solution, IIC drives capacitive touch screen and simulates USB touch device, compatible with computers, mobile phones and other devices.
 
4. Product parameters
Supported screens:
3.95-inch 480X480IPS screen (ST7701S) + GT911 capacitive touch screen
4-inch 480X480IPS screen (ST7701S) + FT6336U capacitive touch screen
4-inch 720X720IPS screen (NV3502C) + FT6336U capacitive touch screen

Interface:
HDMI-C Type interface (mini HDMI interface) * 1
TYPE-C interface * 1

Main control: STC8H8K64U-TSSOP20
Speaker: GSPK2308P-8R1W * 1
Button: Side sticker * 3 (support volume adjustment, brightness adjustment, subsequent firmware update)
Indicator light: Working status indicator light * 1
 
PCB diagram:
5. Instructions for use
According to the schematic diagram, the PCB is soldered. The system is powered by a 5V power supply (can be powered separately by an HDMI cable or a TYPE-C cable), and two 1117 linear step-down outputs 3.3V and 1.8V.
In order to realize the HDMI screen function and USB touch function of the board, the firmware of the two parts needs to be burned separately after the board is welded.
First, for the HDMI screen part, prepare a USB to TTL module, connect its RX, TX, and GND to the 4P pin header on the board, and use the STC-ISP software to burn the firmware. The cold start part is realized by plugging TYPE-C or HDMI to power on the system.
Then for the USB touch part, press and hold the 2P touch button U9, connect the board to the computer via the TYPE-C line, open the WCHISPtool software, select the firmware to burn, and click to download the program.
 
6. Note that
some SMT components do not match: SMD nuts M3 *4 (reserved for PCB fixing, no need to weld).
This module currently verifies the three main functions of HDMI display and audio, USB touch. The WS2812 lamp beads and three touch button circuits are not welded and tested. After the verification is completed, the decorative functions such as RGB lighting effects, button brightness adjustment, and volume will be added. There is no problem with welding all the components.
If you only need HDMI display, you can just plug in an HDMI cable; if you only need USB touch, you can just plug in a TYPE-C cable.
The attachments include:
schematic 
screen and USB touch burning firmware, including Huaxian Technology, Yuxi Technology 4-inch 480X480, 720X720 screen, three sets of firmware.
Complete BOM table and screen purchase link
Welding auxiliary tool, the welding auxiliary tool provides an interactive BOM, which is convenient for hand soldering.

Cost of components: about 58 yuan (excluding WS2812 and touch buttons) LT8619C *1 28.8 yuan
STC8H8K64U *1 4 yuan
 CH554G *1 2 yuan
AMS1117 *2 2 yuan
 CS4344 *1 7 yuan
APA2068 *1 4 yuan
GP2308 speaker *1 2 yuan
RT9293B *1 3 yuan
 Connector + resistor and capacitor components 5 yuan

You can buy the finished board directly in my B station workshop (free shipping without screen), UP host: Qiban Financial Investor
Exchange Group: 227055619
 
Actual picture:
Professional version of LiChuang EDA welding auxiliary tool-interactive BOM:
Shell design:
Display effect:  
Install a 70mm large dichroic prism, the effect please see the attached video demonstration (shell design):