MPU-9150 (I2C) with Labview

[Ian R.]

Originally Posted by RyanN

Sparkfun's example code does a 6-byte burst read. I just checked the AK8975's datasheet and it says is compatible with burst read:


The AK8975 returns a signed 16-bit integer, so negative numbers should return something in the MSB. That's pretty easy to replicate by rotating the sensor 180 degrees.

I'm not sure what's going on from your description. Mind sharing your current LabVIEW code?

Alright, we just rested it and we get values from 79 to -21 when rotating it a full 360 degrees. There's another problem too, the mag returns two equal values for each orientation and it's oposite. So, for instance, if the mag is pointing at 90º, it returns, say, 30. But if it's pointing at -90º, it also returns 30.

Here's the code. We are setting the mag as a slave so we can read the values from the MPU. We alsot tried reading the values directly from the mag, but it's the exact same issue:

Periodic tasks:


MPU Initialize:


Read Compass VI:


Read Burst VI:

[RyanN]

Man that config is long and scary...

The way you're reading the magnetometer looks fine. Just to note, it's not going to give you degrees, but rather, magnetic flux. The data sheet says the values can range from -4096 to +4095 (13-bit signed integer). 4095 represents 1229 µT, and 1 represents 0.3 µT. (micro Teslas) Unless you use a magnet, you're not going to see any readings near those extremes.

http://mythopoeic.org/magnetometer/

It's been a while since I've messed with this stuff, but there is a NOAA calculator that you can use to get an idea of how strong the magnetic flux is in your area.

http://www.ngdc.noaa.gov/geomag-web/

I wouldn't expect anything over 50 µT in our area unless an external source is applied (such as a magnet, motor, electromagnet).

[Ian R.]

Originally Posted by RyanN

Man that config is long and scary...

The way you're reading the magnetometer looks fine. Just to note, it's not going to give you degrees, but rather, magnetic flux. The data sheet says the values can range from -4096 to +4095 (13-bit signed integer). 4095 represents 1229 µT, and 1 represents 0.3 µT. (micro Teslas) Unless you use a magnet, you're not going to see any readings near those extremes.

http://mythopoeic.org/magnetometer/

It's been a while since I've messed with this stuff, but there is a NOAA calculator that you can use to get an idea of how strong the magnetic flux is in your area.

http://www.ngdc.noaa.gov/geomag-web/

I wouldn't expect anything over 50 µT in our area unless an external source is applied (such as a magnet, motor, electromagnet).

Well, we fixed the magnetometer communication at last... But we're having a lot of trouble interpreting the data it gives back. It just doesn't make much sense, even though it reacts as it should.

[uutzinger]

It might be easier to use use the example Arduino code and hook the sensor up to an Arduino and communicate over serial port with Arduino which would read the sensor values and send them to your LabView program.

The 9150 has more than 100 registers and the compass on it is a separate I2C device which the 9150 accesses over its own internal I2C bus.

I recommend code from Kris Winer on github.
Also the 9150 is no longer available and got replaced with 9250 which is mostly compatible except for some of the calibration.

You can also use my code on github (uutzinger). Teensy works well as Arduino replacement.

Making USB serial communication work with RoboRIO is not trivial either.

[Ian R.]

Originally Posted by uutzinger

It might be easier to use use the example Arduino code and hook the sensor up to an Arduino and communicate over serial port with Arduino which would read the sensor values and send them to your LabView program.

The 9150 has more than 100 registers and the compass on it is a separate I2C device which the 9150 accesses over its own internal I2C bus.

I recommend code from Kris Winer on github.
Also the 9150 is no longer available and got replaced with 9250 which is mostly compatible except for some of the calibration.

You can also use my code on github (uutzinger). Teensy works well as Arduino replacement.

Making USB serial communication work with RoboRIO is not trivial either.

Thanks.
At the moment we're sticking with the normal gyro, but we already had the Arduino in mind. One thing that will make that process complicated is opening a communication with the sensor AND the rio at the same time.