accelerometer MPU9250 and SD card module both on SPI wont work together

Hello guys :slight_smile: I am trying to make a datalogger with arduino UNO, MPU9250 (for its 4000Hz capability and 16bit precision) and SD card.


SPI on UNO MPU9250
SD card has CS = 4
and SD card module is conected with MOSI,MISO and CLK lines in parallel with MPU9250.

I took the LowLatencyLogger from sdFat library examples and I try to include into it the MPU9250 library and logg data from sensor to SD card but I have trouble with initialising both devices

If I disconnect the SD module the accelerometer will connect via SPI successfuly (meaning that IMU.begin() will return positive value) but sd card will say:

Can’t access SD card. Do not reformat.
No card, wrong chip select pin, or SPI problem?
SD errorCode: 0X20,0X0

When I try to connect one or the other to the second arduino MEGA for external power that device will stop operating (Dont know why)

Now I just want to read from the WHO_AM_I register to check the connection with the MPU9250.

I tried:

  • Setting the SPI_MODE to 0 after accesing the accelerometer which works with SPI_MODE3 (doesnt work)
  • connecting all to MEGA (I thought maybe UNO isnt able the provide sufficient current)
  • interchange the sequence of initialisation.

The main part of the code begins on line 590.
I commented the IMU.begin() function because it didnt work and I have written manualy the SPI communication below so I know that is going on.

In attachements there is the code and MPU9250 library files.

Thank you for any help. :slight_smile:
EDIT: if I let the script run, but add a 5 second delay in between the MPU SPI initialisation and SD card initialisation and I unglug the SD card module from power and after the initialisation of MPU plug it back in again and let it initialise everything will initialise successfully … what???

MPU9250.cpp (34.7 KB)

MPU9250.h (10.3 KB)

LowLatencyLogger.ino (20.5 KB)

LowLatencyLoggerADXL345_my_2.ino (72 Bytes)

UserFunctions.cpp (2.27 KB)

UserTypes.h (437 Bytes)