2.8inch ESP32-32E E32R28T&E32N28T Display Module User Manual

3.1. Overview of Module Hardware Resources

The module's hardware resources are illustrated in the following figures:

Figure 3.1 Module hardware resources 1: Shows the display module with labels pointing to the LCD and Resistive Touch Screen.

Figure 3.2 Module hardware resources 2: Provides a detailed view of the module's PCB, labeling key components:

• Backlight Control Circuit: Manages the LCD backlight.
• 5V to 3.3V Voltage Regulator Circuit: Regulates power for the module.
• Speaker Interface: For connecting external speakers.
• Audio Power Amplifier Circuit: Amplifies audio signals.
• SPI Interface: Serial Peripheral Interface for communication.
• EESET Key: A key for specific functions.
• Type-C Interface: For power supply and data communication.
• USB to Serial Port and One-click Download Circuit: Facilitates USB to TTL serial communication and program downloading.
• BOOT Key: Used for boot mode selection.
• Battery Charge and Discharge Management Circuit: Manages battery charging and discharging.
• Battery Interface: Connector for battery power.
• Serial Port: For serial communication.
• RGB Three-color Light: Indicates module status with red, green, and blue LEDs.
• MicroSD Card Slot: For expandable storage.
• ESP32-WROOM-32E Module: The core microcontroller unit.

Detailed Component Descriptions:

• LCD: Features a 2.8-inch display with an ILI9341 driver IC and a 240x320 resolution, connected via a 4-wire SPI interface.
• ILI9341 Controller: Supports up to 240*320 resolution, 172800-byte GRAM, various data bus widths (8, 9, 16, 18-bit parallel), and 3/4-wire SPI serial ports. It offers rich color display (65K, 262K RGB) and supports rotating display, scroll display, and video playback. It uses 16-bit (RGB565) for pixel display, allowing up to 65K colors per pixel.
• SPI Communication Protocol: Details the writing mode timing for the 4-wire SPI bus, including chip selection (CSX), data/command control (D/CX), clock (SCL), and data (SDA) lines. It specifies high bit first transmission and discusses CPHA (Clock Phase) and CPOL (Clock Polarity) for SPI communication methods.
• Resistive Touch Screen: A 2.8-inch touch screen controlled by the XPT2046 IC via four pins (XL, XR, YU, YD).
• ESP32-WROOM-32E Module: Features an ESP32-DOWD-V3 chip with a dual-core 32-bit LX6 microprocessor running up to 240MHz. It includes 448KB ROM, 520KB SRAM, 16KB RTC SRAM, and 4MB QSPI Flash. It supports 2.4GHz Wi-Fi, Bluetooth V4.2, and Bluetooth Low Power. It offers 26 GPIOs and supports SD card, UART, SPI, SDIO, I2C, LED PWM, motor PWM, I2S, IR, pulse counter, GPIO, capacitive touch sensor, ADC, DAC, and TWAI.
• MicroSD Card Slot: Utilizes SPI communication mode for high-speed storage with MicroSD cards.
• RGB Three-color Light: Red, green, and blue LEDs used to indicate program status.
• Serial Port: An external serial port module for communication.
• USB to Serial Port and One-click Download Circuit: Uses the CH340C IC for USB to TTL serial conversion and includes a circuit for automatic download mode entry.
• Battery Interface: A two-pin interface for battery power supply and charging.
• Battery Charge and Discharge Management Circuit: Features the TP4054 IC to control battery charging current and safely manage charging and discharging.
• BOOT Key: When pressed during power-on or reset, it lowers IO0, enabling download mode. It can also function as a regular button.
• Type-C Interface: Serves as the primary interface for power supply, program download, and serial communication.
• 5V to 3.3V Voltage Regulator Circuit: Uses the ME6217C33M5G LDO regulator to provide a stable 3.3V output from a 5V input, with a maximum output current of 800mA.
• RESET Key: Pulls down the ESP32 reset pin to perform a reset function.
• Resistive Touch Screen Control Circuit: Employs the XPT2046 IC to read touch coordinates via SPI communication.
• Expand the Pin: Unused IO ports, GND, and 3.3V pins are led out for peripheral use.
• Backlight Control Circuit: Uses a BSS138 field-effect transistor to control the LCD backlight. The backlight is on when the control pin is high and off when low.
• Speaker Interface: Terminals for connecting mono speakers and loudspeakers.
• Audio Power Amplifier Circuit: Utilizes the FM8002E audio amplifier IC to drive small speakers, providing up to 1.5W (8 ohms) or 2W (4 ohms) output at 5V.
• SPI Peripheral Interface: A 4-wire interface that leads out unused chip selection and SPI pins for external SPI devices or general IO use.

3.2. Detailed Explanation of Schematic Diagrams

1) Type-C Interface Circuit:

This circuit includes a Schottky diode (D1) for reverse current prevention and electrostatic surge protection diodes (D2-D4) to protect against overvoltage or short circuits. R1 is a pull-down resistor. The Type-C bus (USB1) handles power supply, program download, and serial port communication. +5V and GND provide power, while USB_D- and USB_D+ are differential USB signals transmitted to the USB-to-serial circuit.

2) 5V to 3.3V Voltage Regulator Circuit:

This circuit uses bypass filter capacitors (C16-C19) to stabilize input and output voltages. The U1 is a ME6217C33M5G LDO regulator, converting the 5V input from the Type-C interface to the required 3.3V for most module circuits.

3) Resistive Touch Screen Control Circuit:

Bypass filter capacitors (C25, C27) stabilize input voltage. Pull-up resistors (R22) maintain default pin states. The XPT2046 control IC (U4) reads touch coordinates through X+, X-, Y+, Y- pins and converts them via ADC, transmitting the values to the ESP32 master for pixel coordinate conversion. The PEN pin acts as a touch interrupt, going low on touch events.

4) USB to Serial Port and One-click Download Circuit:

The CH340C USB-to-serial IC (U3) requires no external crystal. A bypass filter capacitor (C6) stabilizes input voltage. NPN triodes (Q1, Q2) and resistors (R6, R7) facilitate USB to serial conversion and one-click download. The circuit enables USB signal transmission to the ESP32 via RXD and TXD pins. The one-click download principle involves specific high/low level outputs on CH340C's RST and DTR pins, controlling the ESP32's IO0 and reset pins to enter download mode.

5) Audio Power Amplifier Circuit:

An RC filter (R23, C7-C9) and gain adjusting resistors (R10, R13) are used. Smaller R10 increases speaker volume. Coupling capacitors (C10, C11) and a pull-up resistor (R11) are present. JP1 is the speaker port. The FM8002E audio amplifier IC (U5) amplifies the audio DAC signal from AUDIO_IN to the speaker via VO1 and VO2 pins. The SHUTDOWN pin enables the amplifier at a low level.

6) ESP32-WROOM-32E Main Control Circuit:

This section shows the main control circuit of the ESP32-WROOM-32E module, including bypass filter capacitors (C4, C5) and the module itself (U2). Refer to official documentation for internal circuit details.

7) Key Reset Circuit:

Features a key (KEY1), pull-up resistor (R4), and delay capacitor (C3). Upon power-on, C3 charges, grounding the RESET pin. When charged, C3 becomes open, pulling RESET high. Pressing KEY1 grounds RESET and discharges C3. Releasing KEY1 recharges C3, re-grounding RESET until fully charged, then ESP32 resets to normal operation. Adjusting C3 tolerance can modify reset timing.

8) Interface Circuit of Serial Module:

Includes a pitch seat (P2), impedance balancing resistors (R29, R30), a field-effect tube (Q5) for 5V power control, and a pull-down resistor (R31). RXD0 and TXD0 connect to serial pins, with power supplied to other pins. This port connects to the onboard USB-to-serial module.

9) Expand IO and Peripheral Interface Circuits:

Connectors P3 and P4 (4P 1.25mm pitch) expose SPI pins (SPI_CLK, SPI_MISO, SPI_MOSI) shared with the MicroSD card. SPI_CS and IO35 are also available for SPI or general IO use. Note that IO35 is input-only.

10) Battery Charge and Discharge Management Circuit:

Bypass filter capacitors (C20-C23) are used. The TP4054 IC (U6) manages battery charging. R27 sets the charging current (max 500mA). JP2 is the battery connector. A P-channel FET (Q3) and pull-down resistor (R28) form the discharge circuit, supplying power when the Type-C interface has no power.

11) 18P LCD Panel Wire Welding Interface:

A bypass filter capacitor (C24) is present. QD1 is the 48P 0.8mm pitch connector for the LCD panel, providing touch screen signals, LCD voltage, SPI communication, control, and backlight connections. The ESP32 controls the LCD and touch screen via these pins.

12) Download Key Circuit:

Features a key (KEY2) and pull-up resistor (R5). Holding KEY2 during power-on or reset enters download mode. Otherwise, KEY2 functions as a normal key.

13) Battery Power Detection Circuit:

Voltage divider resistors (R2, R3) and bypass filter capacitors (C1, C2) measure battery voltage. The BAT+ signal passes through the divider. BAT_ADC is the voltage across R3, sent to the ESP32 master for ADC conversion. The voltage divider scales the battery voltage (up to 4.2V) for the ESP32's 3.3V ADC range; the obtained value is multiplied by 2 for the actual voltage.

14) LCD Backlight Control Circuit:

Includes a debugging resistance (R24), N-channel field-effect tube (Q4), pull-down resistor (R25), and current limiting resistor (R26). The backlight LED connects in parallel to 3.3V and Q4's drain. High on LCD_BL turns on Q4, grounding the backlight. Low turns off Q4. Reducing R26 increases brightness. PWM signals can also adjust backlight.

15) RGB Three-color Light Control Circuit:

An RGB lamp (LED2) with current limiting resistors (R14-R16). LED2 contains red, green, and blue LEDs with a common anode connection. Control pins IO16, IO17, and IO22 light the LEDs at a low level and extinguish them at a high level.

16) MicroSD Card Slot Interface Circuit:

The SD_CARD1 slot uses pull-up resistors (R17-R21) and a bypass filter capacitor (C26). It supports SPI communication mode for high-speed MicroSD card storage and shares the SPI bus with other peripherals.

3.3. Precautions for Display Module Use

1. When the display module is charging, playing audio via an external speaker, and the screen is active, the total current may exceed 500mA. Ensure the Type-C cable and power supply interface can support this current to prevent insufficient power.
2. During operation, avoid touching the LDO voltage regulator and battery charge management ICs to prevent burns from high temperatures.
3. When connecting IO ports, pay attention to their usage to avoid misconnections and ensure program code definitions match the connections.
4. Use the product safely and reasonably.