MPU9250 | Arduino sketches for MPU9250 9DoF with AHRS sensor fusion

You said you used three wires to connect the GY-91 - VIN, SCL and SDA. You didn't mention GND.

You must connect both GND and VIN for it to work. Use another jumper to connect GND to GND on the ESP32 and try again.

[edit: Errno 19 ENODEV means that the module couldn't find the I2C sensor]

The solutions was:

1. Using extern C: I was using extern C, but included them in the regular way as well and that caused the problem.

_{I originally wrote this answer for this Drones.SE thread and am reposting here.}

The configurable scale ranges for the accelerometer, gyroscope, and magnetometer on the MPU-9250 IMU affect the maximum resolution and range of the reported values.

As you increase the full-scale range setting, the maximum value/rate that can be reported by the IMU before the IMU is saturated increases, but the resolution of the value/rate decreases.

Section 3.1 of the datasheet for the Invensense MPU-9250 has a table that states the "Gyroscope ADC Word Length", which represents how large the values reported over the I²C or SPI interfaces are. In this case, the gyro word length is 16 bits. A 16 bit two's complement binary number (explained wonderfully in this video by Ben Eater) can range from -32768 to +32767.

Take the example of the ±500 °/s full-scale range. The unit resolution of the two's complement value reported by the gyro (aka Least Significant Bit/LSB resolution) in the ±500 °/s full-scale range is: 32767 / 500 = 65.534 LSB/(°/s) (degrees per second per LSB). This is not coincidentally labeled in the graph as the "Sensitivity Scale Factor" for the FS_SEL=1 condition.

According to the datasheet (https://www.invensense.com/wp-content/uploads/2015/02/PS-MPU-9250A-01-v1.1.pdf) page 12,

the default I²C slave address of the MPU9250 is 0b1101000(=0x68=104) or 0b1101001(=0x69=105) depending on the value of pin AD0.

If you use two MPU9250, you can differentiate them by using one with the first address and the other one with the other address by putting a logic LOW on the AD0 pin of the first MPU and a logic HIGH on the AD0 pin of the second MPU.

I think you need a public class if you're gonna use enum outside of that scope. Also, you need an argument in your function and are missing a semi-colon. I am not sure why you are declaring a function inside of a class? But here is your code with those corrections. Hopefully, I was able to help you.