L-ink-card ink screen NFC card

Based on zhihuijun's plan

• Modify the ink screen to Weifeng 2.13 ink screen

• Modify the board shape to a card, with built-in battery design

• Since the Android program of his solution was not open source, he assembled an app by himself.

• • -

The current program is based on an esp32 uploader from WAVESHARE. This software has modified the basic functions of the project and added NFC transmission. There is really very little data transmitted by NFC. I finally made up an Android app based on a personal blog, ST official SDK, and zhihui's hardware program.

Currently, the original Bluetooth upload function is retained, and the NFC upload function is added.

Just take photos -> Grayscale -> Bluetooth or NFC upload ---- The upper limit of FTM MailBox of ST25DV16K is 256 bytes. Based on the characteristics of the screen (212 104pxl), 212 bytes are uploaded at one time, and a total of 104/8 times are uploaded. ----The slave computer receives 212 bytes into the buffer array each time. After 212 104/8 bytes are stored, refresh the screen!

After initially implementing this, I found that many places need to be modified:

1. The EPD display driver circuit package can be replaced by 0603 to reduce the difficulty of welding, and the material of the board can be moved directly (price tag screen, you know). I spent a lot of effort soldering the 0603 resistors and capacitors to the 0403 PCB. I couldn't stand it anymore, so I placed another order and bought the materials. I actually found that there was no need to use such a small package, and the next version can be modified.

2. The power button switch is designed to have a groove on the measuring surface. Just put it in. The NFC channel selection switch no longer uses a pulsator switch, but is replaced by a three-channel MP3 switch. There is really no key switch as small as the original plan, so I connected a flying wire on the board and removed the boost circuit to make space for the buttons. In actual testing, it can be used without boosting.

3. Regarding the overall thickness, actually the battery is not the problem, the problem is the height of the screen. The front of the screen is covered with the acrylic film of the original price tag (about 1mm), plus the height of the screen itself (about 1mm), so the bracket must be thick enough (2mm), and then the main circuit. In order to save thickness, you can use 0.8 or 1. Of course The side groove should be configured to be large enough to place a button.

As for the bottom layer, this version is temporarily exposed because we are not planning to make it all at once, and we are not planning to use acrylic or 3D printing. We are still thinking about using PCB+silica gel or conformal paint.

Depending on the actual needs, add additional functions to the Android program, because currently it only takes photos to generate pictures, and see if there are any other interesting ways to play.

The screen can be changed to another one at will, as long as the interfaces on both Android and ARM are consistent.

ST25DV16K is an ISO15693 protocol. It does not support ISO14443 for public campus cards or meal card access cards. It cannot implement soft simulation and can only use the solution of white card plus hard channel selection, which is a fly in the ointment. In fact, the hardware switch selection here is very troublesome. To achieve multi-channel selection, if you do not use a switch similar to the original solution and want to use a solution such as a mos tube, it needs a power-off saving function, otherwise it needs a battery to continuously power it. Moreover, the pulsator switch in the original plan was really too thick. It really couldn’t be considered a card, it had to be called a box. Here I try to make it into a card as much as possible. According to ideal assumptions, it should be able to reach 5mm. . . .

I hope you can play freely!

Updated on November 2, 2021: I posted the Android program that I put together at the time. It was poorly written. It is recommended to search the source program on Waveshare to compare and see the changes. :)