E-ink screen_8266 driver board_0603_WOS_v0.1

Contents
1. [Product Overview] 2
2. [Design Description] 3
3. [Product Parameters] 3
4. [ESP8266 Pin Assignment] 3 5.
[Test Point Description] 4
6. [Use and Settings] 5
1. Setting of RESE resistor selection switch 5
2. SPI three-wire/four-wire selection 5
3. Program download method 6
7. [Circuit Schematic Diagram] 6 8.
[Derivative Design and Secondary Development Tips] 8
1. About this board design 8
2. Key circuit parameters and selection 8
2.1 [Inductor parameters] 9
2.2 [RESE resistor parameters] 9
2.3 [Boost circuit high voltage capacitor] 9
2.4 [MOS tube parameters] 9
2.5 [Diode parameters] 10
2.6 [FPC socket] 10
3. Available solutions for secondary development 10
3.1 [Lower power consumption design] 10
3.2 [RESE resistors use more common resistance values] 10
3.3 [SPI 3-wire/4-wire selection switch circuit] 10
4. Layout and wiring considerations 11
 
I. [Product Overview]
This product is a universal ESP8266 driver board for 24-pin electronic ink screens, which can realize the driving function of 1.54-inch, 2.04-inch, 2.13-
inch, 2.6-inch, 2.7-inch, 2.9-inch, 3.71-inch, 4.2-inch, 5.83-inch and 7.5-inch black and white screens and three-
color screens. It can drive various 24-pin SPI interface electronic ink screen bare screens launched by manufacturers such as Weixue and Jiaxian. The board is equipped with ESP-12F module (ESP8266 finished module) and supports Arduino development. The hardware pin definition uses the same definition as the Weixue driver board and related program routines, and can be directly tested and developed using the related local routines and WIFI routines provided by Weixue;
Top layer:
Bottom layer:
Overall effect diagram:
 
2. [Design description]
In this project, in terms of circuit design, the reference circuits in the User Guide of the ink screen using the Jinghong (UC***) series IC solution and the Solomon (SSD***) series IC solution are used as references. For subtle differences, a compatible design is adopted, which can be compatible with most of the ink screen products with 24Pin interfaces on the market.
At the same time, considering the requirements of low cost and easy production, the devices are all packaged in a size not less than 0603, which is convenient for manual welding. All devices are located on the top layer of the PCB, which is convenient for welding using a heating table; for some devices with specific parameter requirements, a variety of alternative models are provided for selection.
For users who need miniaturization, customization and re-layout, derivative design and secondary development tips are provided, see the subsequent chapters for details;
 
3. [Product parameters]
Dimensions: 50*35mm;
Power supply: USB Type-C interface for power;
FPC connection direction: top and bottom connection;
USB interface driver: CH340 driver needs to be installed;
Download method: no manual button required, automatic download;
Auxiliary functions: serial communication indicator, reset button, 8266 unused IO lead;
 
4. [ESP8266 pin allocation]
Among them, the pins used to drive the ink screen are defined as follows
SCLK: SPI serial communication clock signal line.
SDI: SPI serial communication data signal line.
RES: ink screen reset signal, low level is valid.
D/C: data/command control pin (high level indicates data, low level indicates command)
CS: SPI chip select pin (low level is valid)
BUSY: electronic paper busy signal. When the electronic paper is refreshed, the BUSY pin sends a busy signal to the main MCU. At this time
, the MCU cannot read and write the electronic paper driver IC; after the electronic paper is refreshed, the BUSY pin sends an idle
state signal. At this time, the MCU can read and write the electronic paper driver IC. (Note: The busy state of the BUSY pin of some models is high level, and some are low level. It cannot be generalized.)
 
V. [Test point description]
This adapter board has test points for measurement. The test points include PREVGH, PREVGL, VCOM, RESE, GDR, and GND. The functions of each test point are as follows:
1) GDR: N-MOS (SI1304BDL/SI1308EDL drive signal test point).
2) RESE: boost circuit feedback current test point.
3) PREVGH: boost circuit positive high voltage test point.
4) PREVGL: boost circuit negative high voltage test point.
5) GND: power supply negative pole (test point voltage common end).
6) VCOM: Test point for the common voltage of the electronic paper.
 
VI. [Use and Settings]
1. Setting of the RESE resistor selection switch
The position of the resistor selection switch is shown in the figure below. When it is turned to the right, the RESE resistor is set to 3R, and when it is turned to the left, the RESE resistor is set to 0.47R.
Different types of ink screens need to match different RESE resistors. Selecting the wrong RESE resistor will cause the electronic paper to display abnormally or fail to refresh the screen. Please refer to the specification of the ink screen model to be used and determine the resistance position according to the resistance value used in the reference circuit;
 
2. SPI three-wire/four-wire selection
As shown in the figure, users can solder the short resistor to switch the electronic ink screen to use 3-line SPI or 4-line SPI.
If the resistor is connected to the two pads on the lower side, the BS pin is connected to GND, and the ink screen is set to 4-line SPI.
If the resistor is connected to the two pads on the upper side, the BS pin is connected to VCC, and the ink screen is set to 3-line SPI.
The program examples provided by manufacturers such as Better Than Weixue and Jiaxian all use 4-line SPI, so the adapter board is also configured as 4-line SPI by default.
 
3. Program download method
1). Make sure the driver of the USB to serial port chip CH340 is installed on the computer;
2). Use a USB Type-c data cable to connect the driver board and the computer. A red power indicator on the board will light up, and the port number of the CH340 identified will appear in the "Port" item in the device manager;
3). Open Arduino IDE or other programming environment you use, select the corresponding serial port number, and burn the development board. At this time, the serial communication indicator on the board will flash with the data flow. The blue light indicates the sending instruction on the computer side, and the green light indicates the receiving instruction. Note: The IO initialization setting should be performed first in the program. Generally, the BUSY control pin is set to input mode, and other IOs are set to output mode.
4). Check whether the setting of the RESE resistor selection switch of the adapter board matches the ink screen to be connected.
5). After the burning is completed, the FPC interface of the driver board is connected to the 24Pin ink screen. Press the reset button, 8266 will reset and automatically run the burned program.
 
VII. [Circuit schematic]
 
VIII. [Derivative design and secondary development tips]
This design is a universal driver board for debugging and testing. Taking into account factors such as cost, ease of use, and easy manual soldering, the external dimensions have not been considered too much for compatibility. Some users may have miniaturization and customization requirements for the board type based on their actual needs, which requires redrawing the layout. When redesigning, users can use this project as a reference, or make secondary improvements based on the original project; some precautions and key parameters in the design are described as follows.
 
1 About the design of this board
The overall circuit of this board is very simple, and a 2-layer board is enough. However, considering that the 4-layer board of LiChuang is also free for proofing, in order to facilitate the proofing of this board together with other 4-layer boards, a 4-layer board is also used; of course, if you want to use a 2-layer board, you can directly delete the two inner electrical layers of VCC and GND in this board. The VCC network has been connected with the wire topology, and the GND has been stitched in the plane; it should be noted that when modifying, the automatic removal of the closed loop setting in the software should be temporarily turned off;
 
2. Key parameters and selection of circuits
 
2.1 [Inductor parameters]
Jinghong series (UC**) IC: 10uH±10%, rated current 1A;
Solomon series (SSD**) IC: 47uH±10%, rated current 0.5A;
(Note: Just choose a power inductor with a DCR resistance as small as possible and a current of more than 0.5A.)
 
2.2 [RESE resistor parameters]
Jinghong series (UC**) IC: 0.47R / 3R;
Solomon series (SSD**) IC: 0.47R / 3R / 2.2R;
(Note: Some screens of SSD chips require 2.2R matching resistors, and 3R can be used directly.)
 
2.3 [Boost circuit high voltage capacitor]
The withstand voltage must be at least 25V, and it is recommended to use 50V withstand voltage standard to increase the margin;
Note that the capacitor of this high voltage part must not use 0402 package, the general model has insufficient withstand voltage value, and the high withstand voltage model of 0603 is also more expensive, so it is advisable to choose 0805 package;
 
2.4 [MOS tube parameters]
The MOS tube is the most likely to have problems in this circuit;
Drain-source voltage (Vdss): at least 25V;
Continuous drain current (Id): greater than 500mA;
Threshold voltage Vgs(th): less than 1.5V;
On-resistance RDS(on): <400mΩ;
Input capacitance (Ciss): <200pF;
(Note: The withstand voltage must be sufficient, the switching speed must be fast, and the RDS(on) must be as small as possible. It is recommended to use Si1304BDL or Si1308EDL. If these two types are really hard to buy, the worst option is to choose AO3400 from the LiChuang Basic Library. The Ciss of AO3400 is relatively large. It is recommended to connect a resistor of several ohms in series or reserve it at the gate;)
 
2.5 [Diode parameters]
Schottky,
DC reverse withstand voltage (Vr): not less than 30V;
average rectified current (Io): not less than 500mA;
reverse current (Ir): <1mA;
the switching frequency should not be too low;
 
2.6 [FPC socket]
24PIN FPC socket with upper and lower contacts, pin spacing 0.5mm.
Note that you should try to choose double-sided contacts on the top and bottom. Some 4.2-inch cable metal contacts are on the top, while others are on the bottom.
 
3. Available solutions for secondary development
3.1 [Lower power consumption design]
In terms of circuit design, you can directly add an analog switch to the front end of the drive circuit to cancel the deep sleep mode of the e-ink screen in the program. Instead, you can directly turn off the power and power on the device, which has the same effect as waking up from the deep sleep mode.
 
3.2[RESE resistors are made up of commonly used resistance values]
The switching circuit shown in the figure above can be used. When S1 is open, RESE = 3R; when closed, RESE ~= 0.47R;
 
3.3[SPI 3-wire/4-wire selection switch circuit]
As shown in the figure, if the SPI mode needs to be set through the switch, the circuit shown in the figure above can be used. The switch S2 in the circuit can be used together with the switch S1 in the RESE resistor switching circuit. A 2-gang SMD dip switch with a 1.27mm pitch is selected to save PCB area;
 
4. Layout and wiring precautions
Pay attention to the safe spacing of the high-voltage circuit wiring. Among them, the maximum voltage of PREVGH and PREVGL to ground can reach ±18V; the maximum voltage difference between PREVGH and PREVGL can reach 36V. The line spacing of the high-voltage part should be appropriately increased, and the ground should be wrapped as much as possible, and as far away from the clock, USB and other signal wiring as possible;