Analog Bicycle Light Schematic

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.
Review and export
Final manufacturing review
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J3
IC1
Manufacturer Part Number
TLC555CDR
C_COMP P2 - C_DARK_DEC P2
R_LDR P1 - R_LDR_BIAS P2
J_USB SHIELD - R_CC1 P2
R_MOTION_PU P2 - S_MOTION 1
D_BOOST K - C_LED_OUT P1
RV_DARK_3P WIPER - U_DARK 1IN-
J_USB VBUS_B - C_USB_IN P1
U_TIMER CONT - C_CTRL P1
GND
U_CHG BAT - J_BAT 1
R_LED_EN_PU P2 - D_AND1 A
GND
J_USB SHIELD - R_CC1 P2
U_CHG BAT - J_BAT 1
GND
U_LED SW - L_BOOST ~
U_CHG BAT - J_BAT 1
GND
R_LED_EN_PU P2 - D_AND1 A
D_CHG A - R_CHG_LED P2
U_CHG BAT - J_BAT 1
GND
R_MOTION_PU P2 - S_MOTION 1
R_LED_EN_PU P2 - D_AND1 A
U_DARK 1OUT - R_DARK_PU P2
U_DARK 1OUT - R_DARK_PU P2
J_USB SHIELD - J_USB SHIELD
J_USB SHIELD - R_CC1 P2
J_USB VBUS_B - C_USB_IN P1
GND
J_USB SHIELD - R_CC1 P2
D_BOOST K - C_LED_OUT P1
U_CHG BAT - J_BAT 1
U_TIMER OUT - D_AND2 K
J_USB SHIELD - J_USB SHIELD
J_USB SHIELD - R_CC1 P2
U_CHG BAT - J_BAT 1
U_CHG BAT - J_BAT 1
J_USB VBUS_B - C_USB_IN P1
U_TIMER THRES - R_TIME P2
J_USB VBUS_B - C_USB_IN P1
R_MOTION_PU P2 - S_MOTION 1
J_USB SHIELD - R_CC1 P2
J_USB VBUS_B - C_USB_IN P1
U_CHG BAT - J_BAT 1
U_CHG BAT - J_BAT 1
U_CHG BAT - J_BAT 1
J_USB SHIELD - R_CC1 P2
C_TIMER_DEC P2 - C_LED_DEC P2
U_CHG BAT - J_BAT 1
GND
U_CHG PROG - R_PROG P1
J_USB SHIELD - R_CC1 P2
U_TIMER THRES - R_TIME P2
D_LED2 K - U_LED FB
J_USB CC2 - R_CC2 P1
J_USB CC1 - R_CC1 P1
D_CHG A - R_CHG_LED P2
R_LDR P1 - R_LDR_BIAS P2
U_DARK 1OUT - R_DARK_PU P2
U_CHG BAT - J_BAT 1
J_USB VBUS_B - C_USB_IN P1
C_COMP P1 - U_LED COMP
D_LED2 K - U_LED FB
U_LED SW - L_BOOST ~
U_CHG CHRG - D_CHG K
U_CHG BAT - J_BAT 1
D_LED2 K - U_LED FB
J_USB SHIELD - R_CC1 P2
U_CHG BAT - J_BAT 1
J_USB SHIELD - R_CC1 P2
U_CHG BAT - J_BAT 1
R_LED_EN_PU P2 - D_AND1 A
U_CHG BAT - J_BAT 1
RV_DARK_3P WIPER - U_DARK 1IN-
U_CHG BAT - J_BAT 1
C_COMP P1 - U_LED COMP
U_TIMER OUT - D_AND2 K
R_MOTION_PU P2 - S_MOTION 1
RV_DARK_3P WIPER - U_DARK 1IN-
D_BOOST K - C_LED_OUT P1
J_USB CC1 - R_CC1 P1
U_TIMER OUT - D_AND2 K
GND
D_BOOST K - C_LED_OUT P1
U_TIMER THRES - R_TIME P2
J_USB SHIELD - R_CC1 P2
C_TIMER_DEC P2 - C_LED_DEC P2
J_USB CC2 - R_CC2 P1
U_CHG BAT - J_BAT 1
C_TIMER_DEC P2 - C_LED_DEC P2
U_DARK 1OUT - R_DARK_PU P2
J_USB SHIELD - R_CC1 P2
GND
R_LDR P1 - R_LDR_BIAS P2
J_USB VBUS_B - C_USB_IN P1
U_CHG CHRG - D_CHG K
GND
C_COMP P2 - C_DARK_DEC P2
GND
J_USB SHIELD - R_CC1 P2
U_CHG BAT - J_BAT 1
U_TIMER CONT - C_CTRL P1
C_TIMER_DEC P2 - C_LED_DEC P2
U_CHG PROG - R_PROG P1
U_LED SW - L_BOOST ~
C8
Capacitance
10nF
D2
C3
Capacitance
100nF
TP4
R2
Resistance
5.1kΩ
C10
Capacitance
10uF
TP1
R9
Resistance
2kΩ
C7
Capacitance
220nF
C1
Not Recommended for New Designs
Capacitance
4.7uF
TP3
R6
Resistance
100kΩ
C12
Capacitance
47uF
C5
Capacitance
100nF
D1
R10
Resistance
0.68Ω
R5
Resistance
100kΩ
R3
Resistance
1kΩ
C6
Capacitance
100nF
R4
Resistance
100kΩ
TP5
C11
Capacitance
1uF
TP2
R7
Resistance
100kΩ
R1
Resistance
5.1kΩ
TP6
C9
Capacitance
10uF
C2
Not Recommended for New Designs
Capacitance
4.7uF
TP
R11
Resistance
1MΩ
C4
Capacitance
100nF
D3
D4
J2
U3
R8
Resistance
8-20kΩ light, ~1MΩ dark
J1
U2
Not Recommended for New Designs
U1
L1
Inductance
10uH
RV1
Resistance
100kΩ
SW1

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Automatic Bike Light — Schematic Markdown
Overview
This schematic implements a fully analog automatic bicycle front light. It uses USB-C charging, a 1S Li-ion/Li-Po battery input, analog darkness and motion detection, a TLC555 timer, diode-OR control logic, and a TPS61165 constant-current boost LED driver. There is no microcontroller and no firmware.
Main Functional Blocks
1. USB-C input / +5V_USB
  • Main components: J_USB, R_CC1, R_CC2, C_USB_IN
  • Important nets: +5V_USB, GND, CC1_RD, CC2_RD
  • J_USB provides the USB-C 5 V input for charging only.
  • R_CC1 and R_CC2 are 5.1 kΩ pull-down resistors on CC1 and CC2.
  • C_USB_IN provides input capacitance on +5V_USB.
2. Li-ion charger
  • Main components: U_CHG (MCP73831T-2DCI/OT), R_PROG, D_CHG, R_CHG_LED, C_CHG_IN, C_BAT
  • Important nets: +5V_USB, BAT_SYS, CHG_PROG, CHG_STATUS_N, CHG_LED_A, GND
  • U_CHG charges a single-cell Li-ion/Li-Po battery from +5V_USB.
  • R_PROG sets the charge current.
  • D_CHG and R_CHG_LED provide charge-status indication.
3. Battery connector / BAT_SYS
  • Main component: J_BAT
  • Important nets: BAT_SYS, GND
  • J_BAT is the external 2-pin JST-PH battery connector.
  • Pin 1 is BAT_SYS / BAT+.
  • Pin 2 is GND.
  • Intended battery is an external protected 1S Li-ion or Li-Po pack.
  • BAT_SYS is approximately 3.0 V to 4.2 V.
4. Darkness detector
  • Main components: U_DARK (LM393DRG4), R_LDR, R_LDR_BIAS, RV_DARK_3P, R_DARK_PU
  • Important nets: BAT_SYS, LDR_SENSE, DARK_REF, DARK_OK, GND
  • R_LDR and R_LDR_BIAS form the light-dependent sensing divider.
  • RV_DARK_3P is the adjustable threshold trimmer.
  • U_DARK compares LDR_SENSE against DARK_REF.
  • DARK_OK is the comparator output and is pulled up to BAT_SYS by R_DARK_PU.
5. Motion detector
  • Main components: S_MOTION, R_MOTION_PU
  • Important nets: BAT_SYS, MOTION_TRIGGER, GND
  • S_MOTION is the vibration/motion switch.
  • R_MOTION_PU pulls MOTION_TRIGGER up to BAT_SYS.
  • Motion produces a low-going trigger pulse on MOTION_TRIGGER.
6. TLC555 timer
  • Main components: U_TIMER (TLC555CDR), R_TIME, C_TIME, C_CTRL
  • Important nets: BAT_SYS, MOTION_TRIGGER, MOTION_ON, TIMER_RC, TIMER_CTRL, GND
  • U_TIMER is a CMOS 555 timer configured as a monostable.
  • R_TIME = 1 MΩ and C_TIME = 47 µF set the on-time, approximately 50 seconds.
  • C_CTRL is a 10 nF control-pin capacitor.
  • The timer output net is MOTION_ON.
7. OR logic
  • Main components: D_OR1, D_OR2, R_LED_EN_PD
  • Important nets: DARK_OK, MOTION_ON, LED_ENABLE, GND
  • D_OR1 and D_OR2 diode-OR the darkness and motion signals.
  • LED_ENABLE goes active if DARK_OK or MOTION_ON is active.
  • R_LED_EN_PD is a 100 kΩ pulldown on LED_ENABLE.
8. TPS61165 LED driver
  • Main components: U_LED (TPS61165DBVT), L_BOOST, D_BOOST, C_LED_IN, C_LED_OUT, R_SENSE
  • Important nets: BAT_SYS, LED_ENABLE, BOOST_SW, LED_OUT, FB, GND
  • U_LED is the constant-current boost LED driver.
  • LED_ENABLE drives the TPS61165 CTRL input.
  • L_BOOST and D_BOOST form the boost converter power path.
  • R_SENSE sets LED current through the feedback path.
  • LED_OUT is the boosted LED-string voltage only, not a general power rail.
9. LED output
  • Main components: D_LED1, D_LED2
  • Important nets: LED_OUT, LED_SERIES_MID, FB, GND
  • D_LED1 and D_LED2 are high-power white LEDs connected in series.
  • Current flows from LED_OUT through D_LED1, then D_LED2, then to the FB current-sense path.
  • High-power LEDs require thermal management.
10. Test points
  • Main components: TP, TP1, TP2, TP3, TP4, TP5, TP6
  • Important nets: +5V_USB, BAT_SYS, GND, DARK_OK, MOTION_TRIGGER, MOTION_ON, LED_OUT
  • Test points expose key power and control signals for bring-up and debugging.
Main Power Nets
  • +5V_USB: USB-C 5 V charging input.
  • BAT_SYS: protected/external 1S battery system rail, approximately 3.0 V to 4.2 V.
  • LED_OUT: boosted LED-string voltage from the TPS61165 driver.
  • GND: common ground net for the whole schematic.
Basic Signal Flow
  1. USB-C provides +5V_USB to the charger.
  2. The charger powers/charges the external battery connected through J_BAT.
  3. The battery/system rail is BAT_SYS.
  4. The darkness detector generates DARK_OK.
  5. The motion detector triggers the TLC555 timer, generating MOTION_ON.
  6. DARK_OK and MOTION_ON are diode-ORed into LED_ENABLE.
  7. LED_ENABLE turns on the TPS61165 LED driver.
  8. The TPS61165 boosts BAT_SYS to LED_OUT and regulates current through the two series white LEDs.
Notes
  • The design is analog-only.
  • No MCU, no Arduino, no ESP32, and no firmware are used.
  • Use an external protected 1S Li-ion or Li-Po battery pack.
  • GND is the common ground net for the schematic.

  • Overview

  • Main Functional Blocks

  • 1. USB-C input / +5V_USB

  • 2. Li-ion charger

  • 3. Battery connector / BAT_SYS

  • 4. Darkness detector

  • 5. Motion detector

  • 6. TLC555 timer

  • 7. OR logic

  • 8. TPS61165 LED driver

  • 9. LED output

  • 10. Test points

  • Main Power Nets

  • Basic Signal Flow

  • Notes

Automatic Bike Light

Automatic Bike Light thumbnail
Fully analog automatic bicycle front light with USB-C charging, 1S Li-ion/Li-Po battery input, darkness detection, motion-triggered timer control, and a TPS61165 boost LED driver. The circuit automatically enables the front LEDs when it is dark or motion is detected, without any microcontroller or firmware.

Properties

Properties describe core aspects of the project.

Pricing & Availability

Distributor

Qty 1

Arrow

$3.36–$6.24

Digi-Key

$2.85

HQonline

$0.77–$0.97

LCSC

$3.86–$4.18

Mouser

$13.25–$24.65

TME

$7.52

Verical

$19.64–$91.41

Controls