Smart LED Flashlight - CH32V003

Smart LED Flashlight - CH32V003 is an open-source, compact, and energy-efficient flashlight solution based on the CH32V003 RISC-V microcontroller and SGM3732 LED driver.

It features multiple adjustable brightness lighting modes (Steady, Breathing, Blinking, SOS), battery monitoring, and zero standby current via a soft latching power circuit.

Designed for DIY enthusiasts, emergency kits, portable lighting, and educational projects.

• Low-cost, minimal component count
• USB or battery powered (3.0V–5.5V)
• Up to 10 LEDs in series
• Advanced features: PWM dimming, SOS mode, battery protection
• Open source hardware and firmware

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• Smart LED Flashlight - CH32V003
  • Circuit on Breadboard
  • Schematic
  • Features
  • Components
    • MCU - CH32V003
      • Clock Selection
      • Battery Monitoring
    • LED Driver - SGM3732
    • Soft Latching Power Circuit
    • LDO - ME6211
  • Minimized ch32fun Library
  • References
  • License

Circuit on Breadboard

Schematic

Features

• Low-cost
• PWM-controlled adjustable brightness
• Supports up to 10 LEDs in series
• Operates from 3.0V to 5.5V (suitable for single cell lithium battery)
• Soft latching power circuit for zero standby current
• Automatic power monitoring and low-voltage lockout to prevent battery drain
• 4 Modes - Steady, Breathing, Blinking, and SOS.
  • Click/Double click Mode button to switch to previous/next mode.
  • Hold Mode button anytime to directly switch to SOS mode.
• 8 Levels
  • Click/Double click Level button to increase/decrease.
  • Hold Level button to switch between min and max.

Components

MCU - CH32V003

The CH32V003 is a low-cost, high-performance 32-bit RISC-V microcontroller from WCH. It features a compact design, low power consumption, and a rich set of peripherals, making it ideal for embedded applications and cost-sensitive projects. The CH32V003 supports various interfaces such as UART, SPI, I2C, and PWM, and is well-suited for controlling LED drivers and other hardware components.

• CH32V003 Datasheet V1.7
• CH32V003 Reference Manual V1.7

Link to More CH32V003 Pinout charts

Clock Selection

With a 1.5MHz clock (1/16 of the internal 24MHz high-speed clock), the CH32V003 draws around 1.53mA (the power LED draws around 1.35mA). With clocks lower than 1.5MHz, CH32V003 does not seem to work properly with ADC enabled and may brick the chip. If this happens, try the unbrick command (minichlink -u) or flash a firmware with a higher clock; note that it may require more than 10 attempts. The chip is quite robust, but recovering it may require patience!

Battery Monitoring

When using a lithium battery as the power supply, and considering the cutoff voltages of the CH32V003 and SGM3732, the lockout voltage is set at 3.0V if detected 3 times.

• CH32V003: 2.8V-5.5V (With ADC).
• SGM3732: 2.7V-5.5V.

Since the power supply can drop below 3.3V, directly using 3.3V as the ADC reference would lead to inaccurate results. Fortunately, the CH32V003 provides an internal voltage reference (1.2V on analog channel 8), which allows for accurate ADC measurements with an error within ±1%.

$$ \begin{align} \text{V}_\text{Reference} &= \text{V}_\text{DD} \times \frac{\text{ADC}_{\text{Reference}}}{1023} \Longrightarrow \text{V}_\text{DD} = \frac{\text{V}_\text{Reference}}{\frac{\text{ADC}_{\text{Reference}}}{1023}} \\ \text{V}_\text{Battery} &= \text{V}_\text{DD} \times \frac{\text{ADC}_{\text{Battery}}}{1023} \\ &= \frac{\text{V}_\text{Reference}}{\frac{\text{ADC}_{\text{Reference}}}{1023}} \times \frac{\text{ADC}_{\text{Battery}}}{1023} \\ &= \text{V}_\text{Reference} \times \frac{\text{ADC}_{\text{Battery}}}{\text{ADC}_\text{Reference}}\\ &= 1.2\ \text{V} \times \frac{\text{ADC}_{\text{Battery}}}{\text{ADC}_\text{Reference}} \end{align} $$

LED Driver - SGM3732

The SGM3732 is a high-efficiency constant current LED driver with a 1.1MHz PWM boost converter, optimized for compact designs using small components. It can drive up to 10 LEDs in series (up to 38V output) or deliver up to 260mA with 3 LEDs per string, while maintaining high conversion efficiency. LED current is programmable via a digital PWM dimming interface (2kHz–60kHz). The device features very low shutdown current and includes protections such as over-voltage, cycle-by-cycle input current limit, and thermal shutdown. The SGM3732 is available in a TSOT-23-6 package and operates from -40℃ to +85℃.

• SGM3732 Datasheet Rev A4
• SGM3732 Datasheet Rev A3 – The older version includes circuit design and component selection guidance.

Soft Latching Power Circuit

Refer to the CH32V003 Soft Latching Power Circuits project.

LDO - ME6211

The CH32V003 operates from 2.7V to 5.5V, but shows noticeable current fluctuations when powered directly from USB. Using an LDO stabilizes the MCU’s power supply and reduces current consumption by a few milliamps.

When the input voltage drops under 3.3V, LDO stops regulate, the output voltage is $\text{V}\text{In} - \text{V}\text{Dropout}$. The dropout voltage is ~2.6mV ($\text{V}\text{In}$ = ~3.3V) to 5mV ($\text{V}\text{In}$ = 2.85V) when the power consumption is ~3mA.

• ME6211 Datasheet - V24

Minimized ch32fun Library

• ch32fun.mk - Some modifications to accommodate library and tool paths.

  • The LDFLAGS path change is for locating the ch32fun/libgcc.a.

    <     LDFLAGS+=-L$(CH32FUN)/../misc -lgcc
    ---
    >     LDFLAGS+=-L$(CH32FUN) -lgcc

    • Otherwise, the compiler would use the default libgcc and throw an incompatible linking error:

      .../riscv64-unknown-elf/bin/ld:
      .../riscv-gnu-toolchain/main/lib/gcc/riscv64-unknown-elf/15.1.0/libgcc.a(div.o):
      ABI is incompatible with that of the selected emulation:
      target emulation `elf64-littleriscv' does not match `elf32-littleriscv'
      

  • The other two changes are for minichlink:

    33c33
    < MINICHLINK?=$(CH32FUN)/../minichlink
    ---
    > MINICHLINK?=$(CH32FUN)
    51c51
    <     LDFLAGS+=-L$(CH32FUN)/../misc -lgcc
    ---
    >     LDFLAGS+=-L$(CH32FUN) -lgcc
    350c350
    <     make -C $(MINICHLINK) all
    ---
    >     # make -C $(MINICHLINK) all

• ch32fun.c

  • Changed line 1728 for 6MHz HCLK, resulting in lower power consumption (<2.6mA).

    1720: #elif defined(FUNCONF_USE_HSI) && FUNCONF_USE_HSI
    1721: #if defined(CH32V30x) || defined(CH32V20x) || defined(CH32V10x)
    1722:     EXTEN->EXTEN_CTR |= EXTEN_PLL_HSI_PRE;
    1723: #endif
    1724: #if defined(FUNCONF_USE_PLL) && FUNCONF_USE_PLL
    1725:     RCC->CFGR0 = BASE_CFGR0;
    1726:     RCC->CTLR  = BASE_CTLR | RCC_HSION | RCC_PLLON; // Use HSI, enable PLL.
    1727: #else
    1728:     RCC->CFGR0 = RCC_HPRE_DIV4;                    // HCLK = SYSCLK / 4
    1729:     RCC->CTLR  = BASE_CTLR | RCC_HSION;             // Use HSI only.
    1730: #endif

  • Set ADC sampling time to 241 cycles for better accuracy.

    1808: // set sampling time for all channels to 0b111 (241 cycles).
    1809: ADC1->SAMPTR2 = (ADC_SMP0<<(3*0)) | (ADC_SMP0<<(3*1)) | (ADC_SMP0<<(3*2)) | (ADC_SMP0<<(3*3)) | (ADC_SMP0<<  (3*4)) | (ADC_SMP0<<(3*5)) | (ADC_SMP0<<(3*6)) | (ADC_SMP0<<(3*7)) | (ADC_SMP0<<(3*8)) | (ADC_SMP0<<(3*9));
    1810: ADC1->SAMPTR1 = (ADC_SMP0<<(3*0)) | (ADC_SMP0<<(3*1)) | (ADC_SMP0<<(3*2)) | (ADC_SMP0<<(3*3)) | (ADC_SMP0<<  (3*4)) | (ADC_SMP0<<(3*5));

References

• Andrew Levido: Soft Latching Power Circuits
• CNLohr: ch32fun
• A Guide to Debouncing
• The simplest button debounce solution
• Museum of the Game - Let's design some POKEY replacements

License

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