Improved version of Link-Card

1. Motive:

• In June 2020, I saw the video of Link card released by Zhihui Jun, and I came up with the idea of ​​replicating one.
  

• I successfully made a replica in 2022, and gained a lot of fans with this
  ~ Click me to watch ~
  

• However, since the forgery was successful, the most popular comments and private messages were about the problems encountered in making the Link and the areas for improvement discovered during use. Here is a part of what I compiled:
  

2.Planning

• Based on the opinions raised by fans, we have made some improved plans. The following are some of the main changes made.
  

3. Major improvements

• 1. Appearance, the middle frame is made of transparent 3D printing, which is divided into upper middle frame and lower middle frame. The cover is cut from acrylic. The printed file and acrylic frame will be placed in the attachment! !
  Fixing method: Use 4 screws on the front and back. The screws on the front are M2x3 and the screws on the back are M2x6.
  
  

• 2. Change the button battery to a lithium battery, model 502025, and match it with the onboard 4056 charging circuit. Due to the small battery capacity, in order to reduce heat generation, the charging current is limited to about 200ma.
  

• 3. The power button is moved to the side, opposite to the dial switch, which facilitates one-handed operation. A function button is added, connected to the stm32 GPIO, with customizable functions. It is used as a power display button by default. How to use: Press the function button and then press the power button to turn on the computer and automatically enter the power display interface. Because the board will pull down the voltage and the power algorithm is not perfect, the power is for reference only and may fluctuate! !

4. What you need to know about PCB

This open source project is a Link motherboard, which can also be used with a Link-link adapter board. Link-link leads to the power supply, download port, and serial port, which can be easily connected to the host computer and downloader. The on-board reset button makes debugging easy.
As shown below, gerber will be placed in the attachment.
Note: The connection uses 8P0.5mm same-direction FPC soft cable, and the serial ports have been crossed (the RXD of the Link-link is connected to the RXD of the computer, and the TXD is connected to the TXD of the computer, no need to cross it again)

5.Code

I reconstructed Zhihui Jun's program, re-ported Weixue's driver, and retained various display APIs, such as string display, picture display, drawing basic graphics, partial refresh, etc.
The code has not been completed yet, and only the .hex file has been released. It can be directly burned and used, or the original program of Zhihui Jun can be directly burned. It is fully compatible, but there is no battery display function.

6.Host computer

Some fans sent private messages saying that their mobile phones did not have NFC function, or they were made by Apple and could not use Zhihuijun’s APP, so they came up with the idea of ​​writing a computer host computer. The software interface is as shown below. No installation is required. Just open it and use it. The software will put In the attachment:

the functions are as follows:
1. Note: You can send what you want to do to Link. Click the note, and an input box will pop up. Enter the content you want to display, click OK, and the ink screen on the left side of the software will be displayed simultaneously, and the serial port scan It can automatically find the available serial port of the computer. Click the serial port to send the data to Link.
2. Picture display: You can load the local picture of the computer and convert it into binary or simulated grayscale before sending it to Link. Click Export.c to save it as c file, so this software can also be used as a mold-taking software.

7. Results chart

Two renderings are shown below. For specific demonstrations, please go to Station B.
Front:

Back:

• Demonstration effect ~Click here to see the effect~

8.Epilogue

• The software part of this project currently only implements a few functions, and many will be added in the future (after all, it is intended to be used as an NFC ink screen development board). If you have good ideas and opinions, you can also leave a message.