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Fault, short circuit on 3.3v in the STM32F303 microcontroller circuit in the basecam

  • I bought the Nebula Slant 5100 gimbal. It works based on IC2 communication. Each motor has its own STM32F103 microcontroller with an engine controller. The YAW motor has a higher version of the STM32F303 microcontroller. This module is equipped with a UART USB converter, for programming the system. In addition, an IMU sensor located on the camera frame works on the IC2 bus.
    The modules are connected to each other by three springbrushes, thanks to which Nebula has no limitation for movements above 360 ​​degrees.
    After a week of work, Nebula stopped responding, a red light flashed in the main microcontroller module. This meant a short circuit in the STM32 circuit between GND and VSS, in the 3.3 V range. Short-circuiting this is manifested by the flashing of the red LED, because the 5V-3.3V stabilizer is equipped with overcurrent protection and picks up.
    In this case I diagnosed the existence of a short circuit on the IC2 bus, on the SDA output.
    After replacing the microcontroller, the GND - VSS short circuit gave way, the voltage on the new microcontroller appeared correctly.
    However, after two days, after the device was assembled, the same fault occurred again, shorting GVD-VSS, and shorting SDA-GND. I did not even have time to program the microcontroller.
    I removed the entire module with the YAW engine. I replaced it with the new original programmed Basecam SimpleBGC32bit. I fed it with two short-circuited microcontroller modules on the PITCH and ROLL axes, and an IMU sensor via the IC2 bus. Unfortunately, after two days when I was able to tune the PID, there was a fault again. This time, apart from shorting VSS - GND on STM32F303, there was a short circuit on both SDA - GND and SCL - GND busses.
    What could be the cause of this vulnerability?
    - the bad section of power supply appearing and disappearing on the microcontroller modules?
    - no contact on bruschring sliders?
    - conflict on the IC2 bus?
    I have no idea.
    How can you protect the microcontroller so it will not be damaged? I noticed that the IC2 bus is unsecured, like a transil diode or even a resistor.
    I can not afford another electronics exchange, in my country Bacecam modules are hard to access and cost twice as much as you.
    An additional question, when I sold a new STM32F303 microcontroller to the Basecam module, how to program it? You need to boot in a special bootloader mode? Is the Bootloader pre-loaded in the lowest memory stack? Do you need to upload your bootloader, and if you can send it? For what outputs is the program for a clean microcontroller loaded? Is it enough to connect to a computer via a USB UART converter?
  • Hello,
    At first, check I2c bus of IMU to shortcircut to gimbal frame. And the best solution will be lay I2c bus without using slip rings.
    Likely, your problem will appear again and again due to bad slip rings.
    As protection you can use zener diode between SDA & SCL lines, like this: http://ybex.com/d/lvar3jjw2kqlt7xsycjy70gqsf3a5jux8m03sj2g.html
    Zener diode should cut voltage higher than 5V.

    About additional question, please, send us photos of both sides of main board (with STM32F303 MCU) in high resolution and place photos here.