External LED not blinking on NUCLEO-WL55JC2 – onboard LEDs work

chandhumallireddy · ‎2026-01-21

Hello STM Community,

I am working with the STM32 NUCLEO-WL55JC2 board using STM32CubeIDE v1.19, and I am facing an issue with external GPIO usage.

What is working:

Project creation, build, and flashing work correctly.
Debugging and programming via ST-LINK work without issues.
Onboard LEDs (LD1, LD2, LD3) blink correctly using GPIO output configuration.

Issue description:

When I connect an external LED to any GPIO pin (for example PA5, PB5, or other GPIO pins), the LED does not blink, even though:

The firmware is flashed successfully.
The GPIO pin is configured as GPIO Output (Push-Pull) in CubeMX.
The pin is toggled in the code using HAL_GPIO_TogglePin() / HAL_GPIO_WritePin().

Key observation:

Onboard LEDs blink as expected.
External LEDs do not blink on any GPIO pin I tried.
The same GPIO toggle logic works for onboard LEDs but not for externally connected LEDs.

Hardware setup:

External LED connected to GPIO pin through a 220Ω–330Ω resistor
LED cathode connected to GND
Board powered via USB

Checks already performed:

Verified GPIO configuration in the .ioc file
Confirmed correct GPIO port and pin usage in code
No alternate function selected for tested GPIO pins
No internal pull-up or pull-down enabled
Default clock configuration (works for onboard LEDs)
Tried both HAL_GPIO_TogglePin() and HAL_GPIO_WritePin()
Tested multiple GPIO pins and multiple LEDs/resistors

Questions / doubts:

Are the external GPIO pins disabled, isolated, or powered differently on the NUCLEO-WL55JC2 board?
Do the GPIO pins on this board require any additional jumper, solder bridge, or power-domain enable to drive external loads?
Are there any board-level constraints related to GPIO current drive or pin routing on this board?
Is there any special configuration required to use GPIO pins for external LEDs on the NUCLEO-WL55JC2?

Since the onboard LEDs work correctly but no external GPIO pin drives an external LED, I suspect this might be related to board-level pin routing, power domain configuration, or hardware setup specific to this NUCLEO board.

Any guidance or clarification would be greatly appreciated.

Thank you.

mfgkw · ‎2026-01-21

Hi,

which LED do you use?

If you connect it from VDD - your resistor - LED - GND, does it light up?

TDK · ‎2026-01-21

What LED are you using? What pin are you using? Check schematic to ensure pin is going where you want. Toggle it and verify with a multimeter to ensure voltage is changing. Both PA5 and PB5 are free and can be used to drive LEDs.

There should be no problem driving an LED with any free GPIO pin.

Sounds like the LED is dead.

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Andrew Neil · ‎2026-01-21

Welcome to the forum.

Please see How to write your question to maximize your chances to find a solution for best results.

As @mfgkw said, please clarify how, exactly, you're connecting the LED - a schematic is far more effective than trying to use words.

Some good, clear photos would help.

Also please post the code you're using - see: How to insert source code

@chandhumallireddy wrote:
I suspect this might be related to board-level pin routing, power domain configuration, or hardware setup specific to this NUCLEO board..

This should be documented in the User Manual for the board - available on the 'Documentation' tab of the Product Page:

https://www.st.com/en/evaluation-tools/nucleo-wl55jc.html#documentation

Also see the board schematics - available on the 'CAD resources' tab:

https://www.st.com/en/evaluation-tools/nucleo-wl55jc.html#cad-resources

PS:

@chandhumallireddy wrote:
Debugging and programming via ST-LINK work without issues..

So you've tried stepping your code in the debugger, and watching the LED as you step?

Have you tried just connecting a voltmeter to the pin which should be toggling?

Are you sure that changes to your code have been successfully built and downloaded?

Which pins, exactly, have you tried?

Have you confirmed that your LED works when connected to VDD and GND ?

A complex system that works is invariably found to have evolved from a simple system that worked.
A complex system designed from scratch never works and cannot be patched up to make it work.

Xagon · ‎2026-01-21

yes it is lighting up, when we use VDD - your resistor - LED - GND,

but when we try to light it up using gpio pin (we are using external led) it is not lighting.

mfgkw · ‎2026-01-21

And which LED do you use?

Can you tell its forward voltage and required current?

Can you measure some voltage at the GPIO pin in use without and with LED connected?