Smartwatch PCB Design Guide
Placed components
5:26
Placed 50 component(s): TP2, TP6, R3, R10, SW1, C11, R12, R6, U1, U6, TP10, C15, TP5, U3, C13, C16, R9, U2, R2, C3, TP4, TP3, C14, C2, SW3, TP9, J2, U7, R5, C4, C10, C1, TP8, R1, R7, J1, C12, DS1, C7, R8, R4, TP7, C5, TP1, R11, SW2, C9, D1, C8, C6
Thought
Work done
- Resized the PCB to 100 × 75 mm, 4-layer, to add routing margin while staying within a common prototype size.
- Re-placed the layout so DS1 remains top-side, while U4/MAX30102 and U5/MLX90614 are on the bottom wrist side, close together near the center beneath the OLED.
- Kept the ESP32-C3 antenna at the edge facing outward, with USB-C, battery connector, switch, and power parts arranged away from the sensor cluster.
- ✅ Skin-touch sensors are now bottom-side and centered under the OLED.
- ✅ OLED remains top-side and antenna placement was preserved at the board edge.
- ❌ Routing is not complete: the latest validation still reported 87 airwires and 12 overlapping-copper issues before the final re-placement, and I could not continue to reroute/validate further.
- ❌ Manufacturing export files were not generated, because export should only happen after DRC is clean.
- Run routing cleanup/autorouting next, then re-check DRC until airwires and copper conflicts are cleared.
- After DRC is clean, generate the Gerber, BOM, and pick-and-place manufacturing package.
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ESP32-C3 Smartwatch PCB Specification
Board Specifications
- Dimensions: 58 mm x 42 mm rounded rectangle
- Corner radius: 5 mm
- Stackup: Standard 2 Layer, 1.5-1.6 mm FR4 target
- Solder mask: Black
- Silkscreen: White
- Surface finish: HASL lead-free target
- Complexity target: <=19 ACU
Wearable Orientation Definition
TOP SIDE (VISIBLE SIDE)
- OLED display: top center, aligned with top glass/display window
- ESP32-C3-WROOM-02-N4: lower center, antenna facing bottom edge with 15 mm keepout
- USB-C connector: bottom center
- Charging circuitry: MCP73831 bottom right; AP2112K near ESP32
- Power/load-share switch: SS12D07VG2 on right edge in VBAT-to-SYS_IN path
BOTTOM SIDE (WRIST CONTACT SIDE)
- MAX30102 only: centered under enclosure wrist-contact sensor window
- Must face directly into skin through mechanical cutout
- No copper or ground plane under the optical area
- No solder mask over sensing region
- Flush or slightly recessed relative to enclosure surface
- Optional ground guard ring around sensor perimeter, avoiding the optical area
SIDE / EDGE COMPONENTS
- MLX90614 IR temperature sensor: top edge or side edge facing outward, away from wrist
- Requires clear line-of-sight IR aperture
- Must not be on wrist-contact side
- Keep 6-8 mm thermal isolation from AP2112K and MCP73831
- No copper pour in direct sensing direction path
Routing Rules
- Standard trace width: 0.25 mm
- Power traces: 0.5-0.6 mm
- Minimum trace/clearance: 0.18 mm / 0.18 mm
- Bottom layer: solid GND plane where not excluded by antenna/optical/IR keepouts
- Add stitching vias around board perimeter where allowed
- USB D+/D- routed first, equal length, parallel, no sharp corners
Corrected Placement Summary
TOP SIDE (User-facing)
- OLED: Top Center
- ESP32-C3: Lower Center, antenna toward bottom edge
- USB-C: Bottom Center
- MCP73831: Bottom Right
- AP2112K: Near ESP32
- Switch: Right Edge
- MLX90614: Top Edge or Side Facing Outward
BOTTOM SIDE (Wrist Contact)
- MAX30102: Centered under enclosure window cutout
CENTER (internal alignment layer)
- MPU6050: Board center of gravity
Enclosure Alignment Rule
- MAX30102 must align with a physical wrist-contact window in the enclosure
- OLED must align with top glass display window
- MLX90614 must align with an external IR aperture opening
- No copper or silkscreen may interfere with optical or IR windows
Electrical Summary
- MCU: ESP32-C3-WROOM-02-N4
- Display SPI: SCK GPIO6, MOSI GPIO7, CS GPIO10, DC GPIO3, RST GPIO2
- I2C bus: SDA GPIO4, SCL GPIO5, 4.7k pull-ups to 3V3 near ESP32
- MAX30102 INT: GPIO8, high-impedance at boot
- MPU6050 INT: GPIO9, high-impedance at boot
- USB D+: GPIO19; USB D-: GPIO18
- Battery ADC divider: 100k/100k to GPIO0 or GPIO1
- EN: 10k pull-up to 3V3 with optional reset button
- Power: USB VBUS to MCP73831; battery through SS12D07VG2 switch to SYS_IN/AP2112K VIN; AP2112K to 3V3; Schottky VBUS to SYS_IN for USB load sharing
Component Choice Decisions
- IMU: Bare MPU-6050 is retained instead of GY-521 module for compact JLCPCB assembly and lower smartwatch stack height.
- Charger: MCP73831 is retained instead of TP4056 because it is already wired, smaller (SOT-23-5), and better for a compact wearable; TP4056 remains an available alternative only if explicitly required.
- Power switch: SS12D07VG2 is the required load-share/power switch part and is used in the VBAT-to-SYS_IN path.
- Battery connector: JST-PH 2-pin J2 uses P1=VBAT/BAT+ and P2=GND/BAT-; polarity must be shown on silkscreen.
Manufacturing Notes
- Prefer JLCPCB Basic/Extended parts and 0603 passives
- Use SOT-23/SOT-23-5/SOD-123/common SMD packages
- Avoid hand-solder-only parts where possible
Board Specifications
Wearable Orientation Definition
TOP SIDE (VISIBLE SIDE)
BOTTOM SIDE (WRIST CONTACT SIDE)
SIDE / EDGE COMPONENTS
Routing Rules
Corrected Placement Summary
TOP SIDE (User-facing)
BOTTOM SIDE (Wrist Contact)
CENTER (internal alignment layer)
Enclosure Alignment Rule
Electrical Summary
Component Choice Decisions
Manufacturing Notes
