The 4-inch spectroscopic prism screen-the HDMI drive board

(This project was first published in Hard Innovation Society, and the development notes of LT have been compiled and posted above. Friends who want secondary development should not miss the 4-inch square USB capacitive touch HDMI screen - Hard Innovation Society (jlc.com) )

1. Product Introduction

A 4-inch square HDMI screen supports two screen resolutions: 480X480 and 720X720, with HDMI audio function and USB touch function. There are two ways to play it. One is to use it as an HDMI screen with touch, and the other is to turn on the mirror display and install a 70mm beam splitting prism on it to turn it into a cool pseudo-holographic HDMI screen.

2. Application Scenarios

• DIY a very compact and mini external display screen for computers, mobile phones, etc. to satisfy the fun of DIY.
• The monitor comes with USB touch function and HDMI audio function, making it more interesting and practical.
• Compatible with 70mm beam splitting prisms on the market, used for DIY pseudo-holographic HDMI screens.

3. Product Overview

• HDMI screen functions:
• Based on LT8619C, the HDMI to RGB driver LCD screen displays images with a refresh rate of 60Hz.
• The onboard HDMI audio circuit is based on the IIS audio power amplifier CS4344+APA2068 dual-channel audio power amplifier solution, with an onboard 8Ω 1W speaker.
• USB touch function: Based on the CH554 solution, IIC drives the capacitive touch screen and simulates USB touch devices, compatible with computers, mobile phones and other devices.

4. Product parameters

• Support screens:
  
  • 3.95-inch 480X480 IPS screen (ST7701S) + GT911 capacitive touch screen
  • 4-inch 480X480 IPS 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
• Buttons: Side sticker*3 (supports volume adjustment and brightness adjustment, firmware will be updated later)
• Indicator light: Working status indicator light*1

PCB schematic:

5. Instructions for use

• Weld the PCB according to the schematic diagram. The system is powered by a 5V power supply (can be powered by an HDMI cable or a TYPE-C cable alone), with two 1117 linear step-down outputs of 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 soldered.
• The first is the HDMI screen part. Prepare a USB to TTL module, connect its RX, TX, and GND to the 4P pin header on the board. Use STC-ISP software to burn the firmware. In the cold start part, plug TYPE-C or HDMI into the system. Implemented after power-on.
• Then comes the USB touch part. Press and hold the 2P touch button U9, connect the board to the computer through the TYPE-C cable, open the WCHISPtool software, select the firmware to be burned, and click to download the program.

6. Remarks

• Some SMT components do not match: patch nut M3 *4 (reserved for PCB fixation, you can not solder if not needed).
• This module currently verifies the three main functions of HDMI display and audio, and USB touch. The WS2812 lamp bead and three touch button circuits have not been soldered and tested. RGB lighting effects, button brightness, volume and other decorative functions will be added after verification is completed. There is no problem with soldering all the components.
• If you only need HDMI display, you can plug in only one HDMI cable; if you only need USB touch, you can plug in only one TYPE-C cable.
• The attachment contains:
  
  • Schematic diagram.
  • Screen and USB touch burning firmware, including Huaxian Technology and Yuxi Technology 4-inch 480X480 and 720X720 screens, three sets of firmware.
  • Full version BOM list and screen purchase link.
  • Welding auxiliary tool, the welding auxiliary tool provides an interactive BOM to facilitate hand welding.
• Board component cost: 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 + RC component 5 yuan
• You can purchase the finished board directly in my B station workshop (free shipping without screen), UP owner: Qiqian Financial Manager.
• Communication group: 227055619

Actual picture:

Professional version of LC EDA welding auxiliary tool - interactive BOM:

Shell design:

Display effect:

Install a 70mm large beam splitting prism. For the effect, please see the attached video demonstration (the shell is being designed):