SPI, I2C and reading schematics

So I got this imu: https://jeanleflambeur.wordpress.com/2014/08/12/10dof-imu/ 

It has 4 jumpers on it – one controls i2c/spi, 2 control the i2c address for the mpu9250 and MS5611 baro and another one is for pull-up resistors when using i2c.

The ‘documentation’ shows which jumpers to use when using i2c and which ones when using spi:


After reading all of this I decided to use SPI, so I switch the i2c/spi jumper and disconnect the pull-up resistors.

One day later I still cannot get it to say anything else than zero. So I switch to I2C thinking the sensor might be bad and voila – it talks. And it talks a lot! Turns out I2C can’t keep up with the data rate I’m interested ( >= 1Khz ) so I try one more time to get SPI to work without any success. After checking everything – wiring, the raspi, software – I take another look at the schematics:http://www.drotek.fr/ftp/schema/mpu9250-ms5611.PDF and notice that the i2c address selection on the MPU9250 is connected to the SDO pin!!! So I disconnected it and finally get some 0xFF along with lots of zeros… Now I’m trying to get it to say something more meaningful than garbage but hey:


4 thoughts on “SPI, I2C and reading schematics

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