• Status: Schematic review
• Rechargeable Wi-Fi/BLE watch built around an ESP32-S3 module.
• Includes an OLED user interface, accelerometer, USB-C charging/programming, battery monitoring, and physical buttons.

• Wrist-worn prototype / production-intent reference design for connected watch firmware.
• Indoor consumer-electronics use; not a medical or safety device.

• Run from a single-cell protected LiPo battery.
• Charge safely from USB-C while operating.
• Program and debug the ESP32-S3 over native USB.
• Display status and watch UI on a 128x64 monochrome OLED.
• Detect motion, orientation, taps, and wake events with a low-power accelerometer/IMU.
• Report battery state of charge and support deep-sleep operation.

• ESP32-S3 Wi-Fi + BLE module with PCB antenna.
• 128x64 I2C OLED interface at 3.3V.
• Low-power I2C accelerometer/IMU.
• USB-C 5V sink with CC resistors and USB ESD protection.
• Single-cell LiPo charger with power-path/load sharing.
• 3.3V buck-boost rail sized for ESP32 radio current transients.
• Battery fuel gauge.
• BOOT, RESET, and three user buttons.

Diagram

• ESP32-S3 module rather than bare RF IC.
• Native USB D+/D- used for flashing and serial/JTAG.
• Antenna zone must be located at the PCB edge with keepout on every copper layer.

• Default assumption: external or board-mounted 128x64 monochrome I2C OLED using SSD1306-compatible signaling.
• Display power can be firmware-controlled if the selected module supports it.

• Low-power 6-axis IMU/accelerometer on the shared I2C bus with interrupt output for wake-on-motion.

• USB-C sink-only input, no USB-PD.
• Charger must provide power-path/load-sharing so the watch can operate while charging.
• Protected 1-cell LiPo battery assumed; nominal 3.7V, operating range approximately 3.0–4.2V.
• Regulated 3.3V buck-boost rail supports the full battery range and ESP32 transmit peaks.
• Default charge current: 200mA, appropriate for a 400mAh or larger cell at 0.5C. Charge-current resistor should be revised for the final battery.

• Dedicated BOOT and RESET buttons.
• Three active-low user buttons with firmware pull-ups or external bias where needed.

• USB VBUS overcurrent protection and transient suppression.
• Low-capacitance ESD protection on USB D+/D-.
• Battery connector polarity must be clearly marked.

• USB-C: 5V input plus USB 2.0 D+/D-.
• Shared I2C bus: OLED, IMU, fuel gauge.
• IMU interrupt to a wake-capable ESP32 GPIO.
• Battery connector: 2-pin compact polarized connector or solder pads, finalized during mechanical design.

• Reference battery: 400mAh protected LiPo.
• Peak rail capability: at least 600mA at 3.3V, with margin and local bulk capacitance.
• Active runtime depends strongly on Wi-Fi and OLED duty cycle; target approximately one day with aggressive sleep/duty cycling.

• See the Power Budget and Design Notes project file for calculations and sizing assumptions.

• SMT assembly, compact wearable PCB, likely 4-layer for RF/USB routing and dense placement.
• Prefer commonly stocked production parts and small packages where practical.
• Final PCB dimensions, OLED FPC/module geometry, battery dimensions, and enclosure constraints remain to be defined before layout.

• Native USB flashing.
• I2C initialization for OLED, IMU, and fuel gauge.
• IMU interrupt wake from light/deep sleep.
• Battery-state reporting.
• Button debounce and wake support.
• Wi-Fi/BLE duty cycling to meet runtime goals.

• ESP32 antenna at an exposed board edge.
• USB-C accessible from enclosure edge.
• OLED centered on the watch face.
• Buttons accessible on board edges.
• Battery located behind PCB/display without entering antenna keepout.

• Use a pre-certified ESP32-S3 module.
• Use a buck-boost regulator rather than an LDO so 3.3V remains regulated across the full LiPo discharge range.
• Use charger power-path management for safe operation while plugged in.
• Use a shared I2C bus to minimize GPIO and routing.
• Selected ESP32-S3-MINI-1-N8, BQ24074RGTR, TPS63020DSJR, BMI270, and MAX17048G+T10.
• Selected a four-wire 0.96-inch SSD1306-compatible OLED module; no OLED reset GPIO is required.
• Battery connector pinout is J2 pin 1 = BAT+, pin 2 = GND, pin 3 = 10k NTC-to-GND.
• USB input and charge-current limits are approximately 500mA and 200mA respectively.

• OLED is monochrome 128x64 and operates at 3.3V over I2C.
• Battery is protected and at least 400mAh.
• No speaker, haptic motor, microphone, GPS, or health sensors are included.
• No touch screen is included; user interaction uses three buttons.
• Final mechanical dimensions are intentionally deferred to the PCB-layout checkpoint.

• Initial architecture established from the request for ESP32-S3, OLED, LiPo charging, and accelerometer.
• Completed library-sourced schematic with USB-C protection/native USB, charger power path, 3.3V buck-boost, MCU support, shared I2C peripherals, and five buttons.