• Dedicated connector: J7
• Pin 1 = GND
• Pin 2 = 5V_MODEM LED supply
• Pin 3 = EXT_BTN_RAW / button sense from the switch contact
• Pin 4 = EXT_BTN_LED_RETURN_SW switched LED return from Q4

• Configure PC13 as a pulled-up input and interpret low = button pressed.
• Configure PB13 as a push-pull output and drive it low during early boot so Q4 stays off.
• Drive PB13 high only when the external pushbutton LED should turn on.
• The off-board button LED supply is sourced from 5V_MODEM, while Q4 still lets firmware switch the LED on and off from U2 PB13.

• Combined external camera and IR connector: U7
  • Pin 1 = GND
  • Pin 2 = 3V3_MCU
  • Pin 3 = CAM_SCLK
  • Pin 4 = CAM_MISO
  • Pin 5 = CAM_MOSI
  • Pin 6 = CAM_CS
  • Pin 7 = IR_ILLUM_3V3_SW
  • Pin 8 = GND
• High-side switch: Q3 P-channel MOSFET
• Default-off bias: R23 pulls the MOSFET gate up to 3V3_MCU
• Gate series resistor: R24

• Drive PB12 low to turn the IR illuminator on
• Drive PB12 high to turn the IR illuminator off
• During early boot, initialize PB12 as a push-pull output and write it high before enabling any feature that could blink or repurpose the pin
• Before entering sleep or standby, drive PB12 high so the illuminator rail is disabled

1. Initialize clocks and system tick.
2. Configure debug-safe GPIO defaults.
3. Configure PB12 as output-high so the IR illuminator stays off.
4. Configure PB13 as output-low so the external pushbutton LED stays off, and configure PC13 with its inactive pull-up before enabling any interrupt on the button input.
5. Bring up the modem control GPIOs.
6. Initialize I2C1 on PB6/PB7.
7. Initialize SPI for the camera on PA5/PA6/PA7 with PB0 as chip select.
8. Initialize the ultrasonic UART on PB10/PB11.
9. Initialize USB DFU / USB device support if needed.

C
// Pseudocode
write_gpio(PB12, 1);          // active-low control, so HIGH = OFF
configure_output(PB12);

void ir_illum_set(bool enable)
{
    write_gpio(PB12, enable ? 0 : 1);
}

• Keep the IR illuminator off by default.
• Enable it only around image capture windows where the camera requires illumination.
• Turn it off immediately after the capture window completes.
• In any sleep, stop, or standby entry path, explicitly force PB12 high first.
• If wake-up code reconfigures GPIOs, restore PB12 high before re-enabling peripherals.

• MCU: STM32L433
• Recommended toolchains: STM32CubeIDE, STM32CubeMX-generated HAL project, or PlatformIO with STM32 target support.
• Primary programming interfaces:
  • SWD through the debug header
  • USB DFU through the native USB FS connection when firmware enables it

• Verify PB12 idles high after reset.
• Verify U7 pin 7 is 0 V in reset / sleep and 3.3 V only when PB12 is driven low.
• Verify camera SPI still operates correctly with the IR rail disabled.
• Verify modem and ultrasonic interfaces remain unaffected when the IR illuminator is switched on and off.
• Verify PC13 idles in the inactive state with the harness connected and changes state only on button press.
• Verify PB13 powers up in the LED-off state and only enables the off-board LED through its dedicated driver stage.