You can not select more than 25 topics
Topics must start with a letter or number, can include dashes ('-') and can be up to 35 characters long.
122 lines
3.9 KiB
122 lines
3.9 KiB
3 years ago
|
# MicroPython MPU-9250 (MPU-6500 + AK8963) I2C driver
|
||
|
|
|
||
|
|
MPU-9250 is a System in Package (SiP) which combines two chips: MPU-6500 which contains 3-axis gyroscope and 3-axis accelerometer and an AK8963 which is a 3-axis digital compass.
|
||
|
|
|
||
|
|
## Usage
|
||
|
|
|
||
|
|
Simple test with never ending loop.
|
||
|
|
|
||
|
|
```python
|
||
|
|
import utime
|
||
|
|
from machine import I2C, Pin
|
||
|
|
from mpu9250 import MPU9250
|
||
|
|
|
||
|
|
i2c = I2C(scl=Pin(22), sda=Pin(21))
|
||
|
|
sensor = MPU9250(i2c)
|
||
|
|
|
||
|
|
print("MPU9250 id: " + hex(sensor.whoami))
|
||
|
|
|
||
|
|
while True:
|
||
|
|
print(sensor.acceleration)
|
||
|
|
print(sensor.gyro)
|
||
|
|
print(sensor.magnetic)
|
||
|
|
print(sensor.temperature)
|
||
|
|
|
||
|
|
utime.sleep_ms(1000)
|
||
|
|
```
|
||
|
|
|
||
|
|
By default the library returns 3-tuple of X, Y, Z axis values for either acceleration, gyroscope and magnetometer ie compass. Default units are `m/s^2`, `rad/s`, `uT` and `°C`. It is possible to also get acceleration values in `g` and gyro values `deg/s`. See the example below. Note that both the MPU6500 and the AK8963 drivers are available as separate classes. MPU9250 is actually a composite of those two.
|
||
|
|
|
||
|
|
```python
|
||
|
|
import utime
|
||
|
|
from machine import I2C, Pin
|
||
|
|
from mpu9250 import MPU9250
|
||
|
|
from mpu6500 import MPU6500, SF_G, SF_DEG_S
|
||
|
|
|
||
|
|
i2c = I2C(scl=Pin(22), sda=Pin(21))
|
||
|
|
mpu6500 = MPU6500(i2c, accel_sf=SF_G, gyro_sf=SF_DEG_S)
|
||
|
|
sensor = MPU9250(i2c, mpu6500=mpu6500)
|
||
|
|
|
||
|
|
print("MPU9250 id: " + hex(sensor.whoami))
|
||
|
|
|
||
|
|
while True:
|
||
|
|
print(sensor.acceleration)
|
||
|
|
print(sensor.gyro)
|
||
|
|
print(sensor.magnetic)
|
||
|
|
print(sensor.temperature)
|
||
|
|
|
||
|
|
utime.sleep_ms(1000)
|
||
|
|
```
|
||
|
|
|
||
|
|
More realistic example usage with timer. If you get `OSError: 26` or `i2c driver install error` after soft reboot do a hard reboot.
|
||
|
|
|
||
|
|
```python
|
||
|
|
import micropython
|
||
|
|
from machine import I2C, Pin, Timer
|
||
|
|
from mpu9250 import MPU9250
|
||
|
|
|
||
|
|
micropython.alloc_emergency_exception_buf(100)
|
||
|
|
|
||
|
|
i2c = I2C(scl=Pin(22), sda=Pin(21))
|
||
|
|
sensor = MPU9250(i2c)
|
||
|
|
|
||
|
|
def read_sensor(timer):
|
||
|
|
print(sensor.acceleration)
|
||
|
|
print(sensor.gyro)
|
||
|
|
print(sensor.magnetic)
|
||
|
|
print(sensor.temperature)
|
||
|
|
|
||
|
|
print("MPU9250 id: " + hex(sensor.whoami))
|
||
|
|
|
||
|
|
timer_0 = Timer(0)
|
||
|
|
timer_0.init(period=1000, mode=Timer.PERIODIC, callback=read_sensor)
|
||
|
|
```
|
||
|
|
|
||
|
|
## Magnetometer Calibration
|
||
|
|
|
||
|
|
For real life applications you should almost always [calibrate the magnetometer](https://appelsiini.net/2018/calibrate-magnetometer/). The AK8963 driver supports both hard and soft iron correction. Calibration function takes two parameters: `count` is the number of samples to collect and `delay` is the delay in millisecods between the samples.
|
||
|
|
|
||
|
|
With the default values of `256` and `200` calibration takes aproximately one minute. While calibration function is running the sensor should be rotated multiple times around each axis.
|
||
|
|
|
||
|
|
NOTE! If using MPU9250 you will first need to open the I2C bypass access to AK8963. This is not needed when using a standalone AK8963 sensor.
|
||
|
|
|
||
|
|
```python
|
||
|
|
from machine import I2C, Pin
|
||
|
|
from mpu9250 import MPU9250
|
||
|
|
from ak8963 import AK8963
|
||
|
|
|
||
|
|
i2c = I2C(scl=Pin(22), sda=Pin(21))
|
||
|
|
|
||
|
|
dummy = MPU9250(i2c) # this opens the bybass to access to the AK8963
|
||
|
|
ak8963 = AK8963(i2c)
|
||
|
|
offset, scale = ak8963.calibrate(count=256, delay=200)
|
||
|
|
|
||
|
|
sensor = MPU9250(i2c, ak8963=ak8963)
|
||
|
|
```
|
||
|
|
|
||
|
|
After finishing calibration the `calibrate()` method also returns tuples for both hard iron `offset` and soft iron `scale`. To avoid calibrating after each startup it would make sense to strore these values in NVRAM or config file and pass them to the AK8963 constructor. Below example only illustrates how to use the constructor.
|
||
|
|
|
||
|
|
```python
|
||
|
|
from machine import I2C, Pin
|
||
|
|
from mpu9250 import MPU9250
|
||
|
|
from ak8963 import AK8963
|
||
|
|
|
||
|
|
i2c = I2C(scl=Pin(22), sda=Pin(21))
|
||
|
|
dummy = MPU9250(i2c) # this opens the bybass to access to the AK8963
|
||
|
|
|
||
|
|
ak8963 = AK8963(
|
||
|
|
i2c,
|
||
|
|
offset=(-136.8931640625, -160.482421875, 59.02880859375),
|
||
|
|
scale=(1.18437220840483, 0.923895823933424, 0.931707933618979)
|
||
|
|
)
|
||
|
|
|
||
|
|
sensor = MPU9250(i2c, ak8963=ak8963)
|
||
|
|
```
|
||
|
|
|
||
|
|
## Gyro Calibration
|
||
|
|
|
||
|
|
TODO
|
||
|
|
|
||
|
|
## License
|
||
|
|
|
||
|
|
The MIT License (MIT). Please see [License File](LICENSE.txt) for more information.
|