• Worn by a child as a light-up badge or decorative toy.
• Powered from one protected 1-cell LiPo battery.
• Recharged from USB-C 5 V.
• Prototype / small-batch production intent.

• Display colorful LED animations across 20 WS2812B-2020-V6 LEDs.
• Use one momentary switch to start/change a light effect.
• Use one SMD slide switch for hard system power off.
• Read the LiPo charger status output in firmware.
• Indicate charge state using one of the 20 RGB LEDs.

• RP2354A MCU in QFN, no BGA.
• 20 addressable RGB LEDs on the top PCB side.
• USB-C power-only charging input.
• Bottom-side MCU, charger, regulator, passives, switch, and connector placement target.
• SMD-first assembly; few or no through-hole components except USB-C mechanical shell stakes if unavoidable.
• Cheap, well-known, LCSC-available parts where possible.

Diagram

• USB-C power-only sink connector with independent 5.1 kΩ CC pull-downs.
• 500 mA-class resettable PTC and VBUS TVS for hot-plug/ESD protection.
• MCP73832 single-cell LiPo charger with STAT output to MCU and 10 kΩ PROG resistor for ~100 mA charge current.
• Battery connector expects a protected LiPo pack; external pack protection is required for child safety unless an on-board protection circuit is added later.
• Slide switch disconnects the system load from the battery while still allowing USB charging.

• AP2112K-3.3 600 mA LDO with 1 µF input/output capacitors plus bulk capacitance for LED transients.
• Firmware must cap LED brightness so steady 3.3 V current stays well below regulator thermal limits.

• RP2354A with internal flash.
• 12 MHz crystal included for robust timing/USB-capable clocking.
• SWDIO, SWCLK, RUN, 3V3, and GND test pads for programming/debug.

• 20 WS2812B-2020-V6 LEDs powered from 3.3 V.
• Data input from RP2354A GPIO through a small series resistor.
• Bulk rail capacitance near the LED chain.

• USB-C: VBUS, GND, CC1, CC2 only.
• Battery: JST PH 2-pin SMD connector, protected 1S LiPo.
• User input: momentary effect switch to MCU GPIO.
• Debug: SWD test pads.
• LED data: one MCU GPIO to LED1 DIN, then cascaded LED DO to next DIN.
• Charger status: MCP73832 STAT open-drain output pulled up to 3.3 V and read by MCU.

• USB input: 5 V nominal.
• Battery: protected 1S LiPo, 4.2 V full, firmware low-battery shutdown recommended around 3.45 V for headroom and cell life.
• LED current budget must be firmware-limited; theoretical full-white 20 × 60 mA = 1.2 A is intentionally not supported by the 600 mA LDO.

• Prefer LCSC/JLCPCB-compatible components.
• Avoid BGA packages.
• Use SMD passives and ICs.
• Top side should contain only the LEDs where possible.
• Bottom side should contain MCU, charger, connector, regulator, switches, and passives.

• Firmware must set a global LED brightness/current limit.
• Firmware reads charger STAT; low means charging, high/open means complete/no charge depending USB/battery state.
• Firmware reads momentary button and debounces it.
• Firmware should monitor battery voltage through ADC divider if populated and shut down or reduce brightness at low battery.

• Badge/wearable shape TBD.
• No exposed sharp metal edges or battery pouch contact points.
• Battery must be mechanically retained and strain-relieved.
• Add rounded PCB corners and lanyard/mounting holes during layout.

• Use a protected LiPo pack rather than exposing an unprotected cell in the first schematic revision.
• Use AP2112K 3.3 V LDO for simplicity and low cost; firmware enforces current limit.
• Use USB-C power-only connector to reduce cost and pin count; programming is through SWD pads.
• Use one RGB LED in the 20-LED chain for charger status instead of a separate LED.

• LED animations are decorative and can be brightness-limited.
• The badge does not need to run at full-white/full-brightness.
• USB data is not required for normal charging.
• User accepts programming through SWD pads or later revision can add USB D+/D-.
• Battery capacity is not yet specified; charge current is initially set to ~100 mA.

• Initial specification created from user requirements.