Analog Bicycle Light Schematic

flux

The current board has no bottom artwork, so I’m adding a centered white product-style panel on bottom silkscreen only, sized to fit within the 45 × 34 mm outline.

flux

The artwork was added, but the layer identifier needs correction from the generic bottom-silkscreen name to this board’s exact Bottom Overlay layer.

flux

The editable layer value is Bottom for standalone artwork on this stackup, so I’m applying that exact layer now.

flux

The artwork is now on the valid bottom-side layer. I’m visually checking the result and running DRC.

flux

The layout checks are clean; I’m explicitly setting the PCB silkscreen color to white so the new bottom artwork renders as intended in 3D.

flux

Updated only the PCB bottom-side artwork: added the bicycle/light graphic, divider lines, five feature descriptions with line icons, and centered “Flux” branding. Silkscreen color is set to white.
Remaining issues:
  • None reported by DRC.
  • Schematic, electrical connections, component placement, and routing were unchanged.
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Simple Analog Smart Bike Light — Design Notes
Scope
Fully analog automatic bicycle front light. No microcontroller, no Arduino, no ESP32, and no firmware.
Implemented blocks
  • USB-C 5 V charging-only input with 5.1 kΩ CC1/CC2 pulldowns and input capacitance.
  • MCP73831 1S Li-ion/LiPo charger with charge LED and JST-PH battery connector J_BAT.
  • External protected 1S Li-ion/LiPo battery pack only; no fixed PCB battery component. BAT_SYS range is approximately 3.0–4.2 V.
  • LDR + LM393 darkness detector with adjustable threshold. DARK_OK is intended high when dark.
  • SW-18010P vibration switch with 100 kΩ pull-up. MOTION_TRIGGER produces low pulses on movement.
  • TLC555 CMOS timer monostable with R_TIME = 1 MΩ and C_TIME = 47 µF, approximately 50 seconds.
  • Diode-OR logic combines DARK_OK and LED_CONTROL into LED_ENABLE.
  • TPS61165 boost constant-current LED driver powered from BAT_SYS, enabled by LED_ENABLE.
  • Two Cree XP-G3 high-power white LEDs in series.
  • Test points: +5V_USB, BAT_SYS, GND, DARK_OK, MOTION_TRIGGER, LED_CONTROL, LED_OUT.
Important implementation note
The requirements contained a conflict: strict 555 RESET control by DARK_OK would block motion-only operation in bright conditions, while the later requirement explicitly requested OR logic. This schematic prioritizes the explicit OR logic: LED_ENABLE is asserted if darkness OR motion timer output is active. The timer RESET is tied enabled to BAT_SYS.
Production notes
  • Use a protected Li-ion/LiPo battery pack or add a dedicated battery protection circuit before production.
  • Confirm TPS61165 sense resistor and compensation/output values against the exact selected LED current target and LED Vf bin before layout.
  • High-power LEDs require thermal management: copper area, thermal vias, or an external heatsink.
  • Replace RV_DARK placeholder with an actual 100 kΩ trimmer potentiometer footprint before PCB layout.
  • The MOSFET low-side switch was included per request, but the preferred high-quality control path is the LED driver EN/CTRL input via LED_ENABLE.

  • Scope

  • Implemented blocks

  • Important implementation note

  • Production notes