Custom ESP32 MP3 Player Board

This project is a custom ESP32-based board for a small-group MP3 player project.
It is modeled after the SparkFun Thing Plus ESP32-WROOM design.

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Main Components

1. ESP32-WROOM-32D (U2)

   • Main microcontroller with WiFi and Bluetooth
   • Handles all digital I/O, ADC, DAC, SPI, UART, I2C, and GPIO for user buttons
   • Powered by 3.3V logic and supply

2. MCP73831 (U1)

   • Li-Ion/Li-Poly battery charge controller
   • Charges LiPo battery from USB 5V
   • VBAT connects to battery positive terminal
   • STAT output drives charge status LED

3. CH340C (U4)

   • USB-to-Serial converter
   • Interfaces ESP32 UART0 with USB-C
   • Handles serial communication and code uploading
   • DTR and RTS control ESP32 auto-reset and boot via transistors

4. USB-C Connector (CN1 / USB1)

   • USB data and power interface
   • D+ and D– connect to CH340C
   • VBUS (5V) powers charging circuit and regulator
   • CC1 and CC2 resistors identify the board as a USB peripheral

5. Power Path MOSFETs

   • Automatic power source switching
   • Manages USB and battery input without backfeed

6. 3.3V Voltage Regulator (U5)

   • Converts VBAT or USB 5V to 3.3V
   • Powers ESP32 and peripherals

7. MicroSD Card Slot (CARD)

   • SPI interface to ESP32
   • Used for external storage (music files, data, etc.)

8. RGB LED (D12)

   • Addressable WS2812-type LED
   • Controlled via GPIO2
   • Used for status indication

9. Reset and Boot Buttons (SW1, SW2)

   • Reset (EN) restarts ESP32
   • Boot (IO0) forces programming mode when held on reset

10. JST-PH Battery Connector (J1)

    • 2-pin LiPo connector (2.0mm pitch)
    • Pin 1 = VBAT (+)
    • Pin 2 = GND (–)

11. User Buttons (SW3–SW7)

    • 5 pushbuttons connected to ESP32 GPIOs 32, 33, 25, 26, 27 respectively
    • Wired active-LOW with internal pull-ups enabled

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Programming & Pin Setup

Target Board: ESP32 (e.g. ESP32-WROOM-32 / ESP32-WROOM-32E)
IDE: Arduino IDE or PlatformIO
Board Selection: ESP32 Dev Module or equivalent

SD Card Interface (SPI)

Function	ESP32 Pin
CS (Chip Select)	GPIO 5
SCK (Clock)	GPIO 18
MISO	GPIO 19
MOSI	GPIO 23

User Buttons

Button	GPIO	Notes
1	27	Active-LOW, internal pull-up enabled
2	26	Active-LOW, internal pull-up enabled
3	25	Active-LOW, internal pull-up enabled
4	33	Active-LOW, internal pull-up enabled
5	32	Active-LOW, internal pull-up enabled

Baud Rate: 115200 (Serial Monitor)
Power: 3.3V logic level throughout (shared with ESP32 core and SD module)

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Images

The following are images of the schematic, PCB layout, and 3D board render.