• Status: Draft / electronics-first prototype
• Battery-powered ESP32-S3 controller board for a Waveshare 3.5-inch capacitive-touch LCD.
• Mechanical package and final PCB envelope are provisional until the display mounting and enclosure are defined.

• Portable, rechargeable touch-interface device with an external I2C sensor.
• First build is a functional prototype suitable for firmware and sensor validation.

• Run an ESP32-S3 from USB-C or a 3.7 V, 1000 mAh single-cell LiPo battery.
• Drive the Waveshare 3.5-inch 320 x 480 IPS LCD through 4-wire SPI.
• Read the FT6336U capacitive touch controller through I2C.
• Expose SCL, SDA, 3.3 V, and GND for an external sensor.
• Show battery state in the user interface and provide a physical charging indicator.
• Turn on from a momentary pushbutton and allow firmware to shut the system down after an idle timeout.
• Retain USB-C charging while the main system is switched off.

• ESP32-S3 module with Wi-Fi, BLE, and native USB programming.
• USB-C 5 V input with ESD protection and USB 2.0 D+/D- connection.
• Single-cell LiPo charger with power-path operation.
• Efficient regulated 3.3 V system rail across the battery discharge range.
• Dedicated soft-power controller: pushbutton turn-on and MCU-commanded power-off.
• Battery fuel gauge for percentage estimation.
• SPI LCD, I2C touch, optional display microSD chip-select connection.
• External four-pin I2C sensor connector.

• Off-board display module: Waveshare SKU 29318, approximately 61.00 x 92.44 mm.
• Display connection uses the supplied 15-pin GH1.25 cable/interface.
• Battery is an off-board protected 3.7 V, 1000 mAh LiPo pack.
• Final enclosure, button position, connector access, mounting holes, and PCB outline remain provisional.

Diagram

• ESP32-S3 module rather than a bare RF chip.
• Boot and reset controls included; strapping pins kept free of incompatible loads.

• USB-C sink operation without USB-PD.
• Charger target: approximately 500 mA charge current for the 1000 mAh cell, subject to the battery manufacturer's permitted charge rate.
• Charging remains active while the main 3.3 V rail is off.

• Momentary button powers the system on.
• ESP32 firmware asserts a shutdown/clear signal after the configured idle period.
• Main regulator is disabled during off state to minimize drain.

• Waveshare 3.5inch Capacitive Touch LCD, SKU 29318.
• LCD: ST7796S, 320 x 480, 4-wire SPI.
• Touch: FT6336U, I2C with interrupt and reset.
• Module operates at 3.3 V or 5 V; this board uses 3.3 V supply and 3.3 V logic.

• Four-pin external connector: 3V3, GND, SDA, SCL.
• Shared I2C bus with touch controller and fuel gauge; one pull-up pair on the controller board.
• Initial external sensor current allowance: 100 mA maximum.

• Fuel-gauge IC reports state-of-charge to firmware for the on-screen battery icon.
• Charger status output drives a physical charge LED.

• USB-C: 5 V input plus native ESP32-S3 USB 2.0 D+/D-.
• Battery: two-pin polarized connector for one protected LiPo cell.
• Display: 15-pin GH1.25 interface including power, SPI, touch I2C, interrupt/reset, backlight, and microSD chip select.
• Sensor: 4-pin I2C connector.
• User controls: power, reset, and boot buttons.

• Nominal battery: 3.7 V, 1000 mAh; design discharge range assumed 3.0-4.2 V.
• Estimated active runtime is roughly 2.5-3.5 hours depending on Wi-Fi use, backlight brightness, and sensor load.
• Idle timeout is firmware configurable; shutdown removes power from the ESP32 and display.
• Target off-state battery drain: below 30 uA, excluding the battery pack's own protection circuit.

• See the separate Power Budget project file.
• 3.3 V regulator design target: at least 0.8 A continuous and approximately 1 A transient capability, verified at minimum battery voltage.

• Hybrid THT/SMD prototype intended to maximize hand-assembly and repairability.
• Use axial through-hole resistors, radial/disc through-hole capacitors where electrically suitable, through-hole charging LED and tactile buttons, and through-hole battery/sensor connectors.
• Retain SMD for the ESP32-S3 module, USB-C receptacle, charger, soft-power controller, buck-boost regulator, fuel gauge, ESD array, display connector, USB series resistors, regulator feedback resistors, switching-regulator capacitors, and mandatory high-frequency local ceramic/bulk decoupling.
• Prefer common, documented components with manufacturer datasheets and verified library footprints; do not trade regulator stability, USB signal integrity, or ESP32 transient performance for a higher THT count.
• Final stackup and board dimensions are deferred to layout.

• Native USB programming/debug.
• GPIO-controlled power shutdown.
• Display backlight PWM/enable control.
• SPI LCD and optional microSD sharing the SPI clock/data lines with separate chip selects.
• I2C touch, battery gauge, and external sensor.
• Touch interrupt available as a wake/activity input while powered.

• ESP32 antenna placed at a board edge with a copper/component keepout.
• USB-C, battery, display, sensor, and power-button connectors must remain enclosure-accessible.
• Display module footprint and mounting geometry must be confirmed before enclosure and final PCB sizing.

• Electronics-first prototype; enclosure work is deferred.
• Use an ESP32-S3 RF module.
• Use 3.3 V for both display power and logic.
• Use a power-path charger plus buck-boost regulator rather than powering directly from the LiPo.
• Use a dedicated pushbutton power controller rather than relying only on ESP32 deep sleep.
• Selected charger/power path: BQ24074RGTT, configured for approximately 500 mA charge and input current.
• Selected main regulator: TPS63070RNMR with XFL4020-152MEC 1.5 uH inductor and 470 kΩ / 150 kΩ feedback divider for 3.3 V.
• Selected soft-power controller: LTC2955CDDB-1#TRPBF; its active-high enable drives the TPS63070 EN pin, GPIO4 drives KILL, and GPIO5 receives the power-button interrupt.
• Selected fuel gauge: MAX17048G+T10, powered directly from BAT so state of charge remains available across system shutdowns.
• GPIO mapping is fixed in the Firmware Getting Started project file.

• Battery includes a protection circuit and permits at least 500 mA charging and 1 A peak discharge.
• External sensor uses 3.3 V I2C logic and draws no more than 100 mA.
• The 15-pin Waveshare interface is used rather than the 18-pin 0.5 mm FPC interface.
• MicroSD support is wired where practical but is not required for first firmware bring-up.

• Initial specification created from user requirements and verified Waveshare product documentation.
• Schematic implementation selected BQ24074 + LTC2955-1 + TPS63070 power architecture, MAX17048 fuel gauge, ESP32-S3-WROOM-1-N8R8, native USB protection, and the final display/sensor GPIO map.
• Display connector J2 uses a real 15-position 1.25 mm library connector; its exact mechanical mating with the requested GH-family cable remains a layout-stage verification item.
• Revised to a hybrid THT/SMD construction strategy: J3/J4, LED1, SW1-SW3, most resistors, and non-critical capacitors are through-hole; high-frequency and power-stage parts remain SMD.