SPI & I2C not working when Nucleo-WB55 powered by external source

DPiór.1 · ‎2025-09-03

I'm working with an STM32WB55 Nucleo board and encountering a strange issue. My project uses an SPI display and an I2C accelerometer, along with BLE.

When the board is powered via the ST-Link/USB, everything works perfectly: the BLE functions, the onboard LEDs toggle, and both the SPI display and I2C accelerometer work as expected.

However, when I try to power the board from a Nordic Power Profiler Kit (PPK) and remove the jumpers as instructed to isolate the ST-Link (see attached image), the SPI display and I2C accelerometer stop working entirely. The BLE and LED toggling functions continue to work correctly, which is puzzling.

Why would the peripherals fail in this specific power configuration, while the rest of the code continues to run? Any insights into what could be causing this are greatly appreciated.

Andrew Neil · ‎2025-09-03

Have you checked that the SPI display and I2C accelerometer are receiving power?

Look carefully at the board schematics to check power routing.

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.