Struggling with Powering up STM32L432 using VIN of +7V

Dave001 · ‎2025-10-19

Hi All,

I am a newbie to STM32L432 boards. I am seeing that when i power the STM32L432 board with USB then everything is fine and my code runs and LED stays solid RED.

But if i try to start the STM32 board with only VIN i.e. +7V then the RED led i.e. LD1 keeps blinking. I have checked that i followed this -

This procedure also works fine -

1) Power up the board using VIN of +7V and LD1 keeps blinking.

2) Connecting USB then the LED LD1 turns to solid RED and then disconnect that cable after 5 seconds.

3) Then continue to use this.

I am guessing here that it is something to do with the bootloader not being able to run from Flash ? But how come just connecting the USB makes it run fine. Is this a known bug ?

Dave001 · ‎2025-10-20

This problem is already resolved by Solved: STM32L432 Nucleo-32 External Power - STMicroelectronics Community

Thank you all for Commenting. Much appreciated.

View solution in original post

Ozone · ‎2025-10-20

> 1) Power up the board using VIN of +7V and LD1 keeps blinking.

Which sounds a bit strange, but I suppose your board has an additional input for a DC power jack.
Mind you, the quoted document says "7V < VIN < 12V", which means +7V is the minimum required. I would try +9V, supposedly the nominal value.

> But if i try to start the STM32 board with only VIN i.e. +7V then the RED led i.e. LD1 keeps blinking.

I suggest to look up in the manual what that blink code means, but usually indicates a power supply issue.
I recently had Raspberry Pis crashing during operation due to power supply issues, and years ago an instance with a STM32 discovery board and an attached LCD display.

Andrew Neil · ‎2025-10-20

Welcome to the forum.

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

You haven't said which Board you are using, but your screenshot looks like this:

https://www.st.com/resource/en/user_manual/um1956-stm32-nucleo32-boards-mb1180-stmicroelectronics.pdf#page=43

Which applies to the NUCLEO-L432KC Nucleo-32 board - is that the one?

@Dave001 wrote:
LED stays solid RED.?

Which LED?

If we're talking Nucleo-32, it has three LEDs - their functions are described in the User Manual

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.

TDK · ‎2025-10-20

> But if i try to start the STM32 board with only VIN i.e. +7V then the RED led i.e. LD1 keeps blinking.

This is the expected behavior. LD1 indicates a USB connection. If the USB cable isn't connected, the expected state is this will continue to flash red forever.

If you feel a post has answered your question, please click "Accept as Solution".

Dave001 · ‎2025-10-20

Apologies board is Nucleo STM32L432.

LED is LD1. It keeps blinking when i power up the device using VIN of +7V and code which i had programmed into it do not run.

LED LD1 stops blinking as soon as USB is connected and my code starts to run.

Dave001 · ‎2025-10-20

Apologies board is Nucleo STM32L432 and voltage is actually 7.3V

I checked that it is waiting for USB Initializations.

LED is LD1. It keeps blinking when i power up the device using VIN of +7V and code which i had programmed into it do not run.

LED LD1 stops blinking as soon as USB is connected and my code starts to run.

Dave001 · ‎2025-10-20

LED is LD1. It keeps blinking when i power up the device using VIN of +7V and code which i had programmed into it do not run.

LED LD1 stops blinking as soon as USB is connected and my code starts to run.

I would like my code to run when it is powered up by VIN which is around 7.3V

Dave001 · ‎2025-10-20

This problem is already resolved by Solved: STM32L432 Nucleo-32 External Power - STMicroelectronics Community

Thank you all for Commenting. Much appreciated.