nanoFramework.Iot.Device.Bmi270 1.0.6

BMI270 - accelerometer and gyroscope

The BMI270 is a 6-axis IMU (Inertial Measurement Unit) from Bosch Sensortec that combines a 3-axis accelerometer and a 3-axis gyroscope. It is designed for wearable and IoT applications and includes advanced features such as step counting and gesture recognition.

Key features:

• Accelerometer programmable FSR of ±2g, ±4g, ±8g, and ±16g
• Gyroscope programmable FSR of ±125 dps, ±250 dps, ±500 dps, ±1000 dps, and ±2000 dps
• Internal temperature sensor
• Built-in step counter, activity recognition, and wrist gesture features
• Auxiliary I2C master interface (used for connecting a BMM150 magnetometer on the M5Stack CoreS3)

Documentation

• Datasheet
• Bosch BMI270-Sensor-API — reference C implementation and config file
• This sensor is used on the M5Stack CoreS3 development kit.

Important: Firmware Config Upload

Unlike simpler IMU sensors, the BMI270 requires an 8 KB configuration file to be uploaded via I2C after every power-on reset. This binding handles this automatically during initialization. The config file is sourced from the Bosch BMI270-Sensor-API (BSD-3-Clause licensed).

Usage

Create the Bmi270AccelerometerGyroscope class and pass the I2C device. The default I2C address is 0x68 (SDO=GND), and the secondary address is 0x69 (SDO=VDDIO). The M5Stack CoreS3 uses address 0x69.

The sample in this binding is adjusted for the M5Stack CoreS3. It follows M5Stack's documented CoreS3 configuration and the official M5Unified source by enabling the CoreS3 internal sensor bus through the AW9523B and then applying the AXP2101 rail profile before talking to the BMI270.

Debug.WriteLine("BMI270 sample adjusted for the M5Stack CoreS3.");

// CoreS3 internal I2C bus: G12 SDA / G11 SCL.
Configuration.SetPinFunction(12, DeviceFunction.I2C1_DATA);
Configuration.SetPinFunction(11, DeviceFunction.I2C1_CLOCK);

EnableCoreS3InternalBusPower();
EnableCoreS3SensorPower();

I2cConnectionSettings settings = new(1, Bmi270AccelerometerGyroscope.SecondaryI2cAddress);

using (Bmi270AccelerometerGyroscope imu = new(I2cDevice.Create(settings)))
{
    Debug.WriteLine("BMI270 initialized successfully!");

    Debug.WriteLine("Start calibration ...");
    var offset = imu.Calibrate(1000);
    Debug.WriteLine($"Calibration done, calculated offsets X:{offset.X} Y:{offset.Y} Z:{offset.Z}");

    Debug.WriteLine($"Internal temperature: {imu.GetInternalTemperature().DegreesCelsius} C");

    while (true)
    {
        var acc = imu.GetAccelerometer();
        var gyr = imu.GetGyroscope();
        Debug.WriteLine($"Accelerometer data x:{acc.X} y:{acc.Y} z:{acc.Z}");
        Debug.WriteLine($"Gyroscope data x:{gyr.X} y:{gyr.Y} z:{gyr.Z}\n");
        Thread.Sleep(100);
    }
}

Sample output

BMI270 initialized successfully!
Start calibration ...
Calibration done, calculated offsets X:12.345 Y:-6.789 Z:3.210
Internal temperature: 28.5 C
Accelerometer data x:-0.041 y:0.003 z:1.012
Gyroscope data x:0.183 y:-0.427 z:-0.091

Accelerometer data x:-0.039 y:0.001 z:1.009
Gyroscope data x:0.122 y:-0.381 z:-0.067

See samples for a complete sample application.

Calibration

The gyroscope can be calibrated using the Calibrate function. During calibration, keep the sensor still and in a fixed position (e.g. lying flat on a table).

var offset = imu.Calibrate(1000);
Debug.WriteLine($"Calibration done, offsets X:{offset.X} Y:{offset.Y} Z:{offset.Z}");

You can also write directly to the compensation registers using SetGyroscopeOffset.

Note: When the device reboots, the offset registers are cleared. Persist calibration data yourself if needed.

Output Data Rate (ODR)

The accelerometer and gyroscope output data rates can be configured at construction time or changed at runtime:

// Set ODR during construction
using var imu = new Bmi270AccelerometerGyroscope(
    I2cDevice.Create(settings),
    accelerometerOdr: AccelerometerOutputDataRate.Odr200Hz,
    gyroscopeOdr: GyroscopeOutputDataRate.Odr400Hz);

// Or change at runtime
imu.AccelerometerOdr = AccelerometerOutputDataRate.Odr50Hz;
imu.GyroscopeOdr = GyroscopeOutputDataRate.Odr100Hz;

Sleep mode

The sensor can be put in suspend mode to save power:

imu.Sleep();
// ... later ...
imu.WakeUp();

Step counter and activity recognition

The BMI270 has a built-in step counter and activity recognition engine. Enable it after initialization:

// Enable step counter with activity recognition
imu.EnableStepCounter(enableActivityRecognition: true);

// Read the step count
int steps = imu.GetStepCount();
Debug.WriteLine($"Steps: {steps}");

// Read the current activity
ActivityType activity = imu.GetActivity();
Debug.WriteLine($"Activity: {activity}"); // Still, Walking, Running, or Unknown

// Reset step counter to zero
imu.ResetStepCounter();

// Disable when no longer needed
imu.DisableStepCounter();

Interrupts

The BMI270 has two interrupt pins (INT1, INT2) that can be configured for various sources:

// Configure INT1 as push-pull, active-high
imu.ConfigureInterruptPin(1, outputEnable: true, activeHigh: true, openDrain: false);

// Map step counter interrupt to INT1
imu.MapFeatureInterrupt(1, FeatureInterruptSource.StepCounter);

// Map data-ready interrupt to INT1
imu.MapDataInterrupt(1, DataInterruptSource.DataReady);

// Read interrupt status (clears latched status)
var featureStatus = imu.GetFeatureInterruptStatus();
var dataStatus = imu.GetDataInterruptStatus();

FIFO

The BMI270 has a 6 KB FIFO buffer for efficient burst reads:

// Enable FIFO for accelerometer and gyroscope, 512-byte watermark
imu.EnableFifo(enableAccelerometer: true, enableGyroscope: true, watermarkBytes: 512);

// Read available data
int available = imu.GetFifoByteCount();
SpanByte buffer = new byte[available];
int bytesRead = imu.ReadFifo(buffer);
// In headerless mode: each frame = 12 bytes (6 acc + 6 gyro), little-endian int16

// Flush FIFO
imu.FlushFifo();

// Disable FIFO
imu.DisableFifo();

9-axis with BMM150 magnetometer (M5Stack CoreS3)

On the M5Stack CoreS3, the BMM150 magnetometer is connected through the BMI270's auxiliary I2C interface. This binding provides a Bmm150I2cBmi270 adapter that allows the existing Bmm150 binding to communicate with the magnetometer through the BMI270.

This sample is adjusted for the M5Stack CoreS3 board bring-up. Before creating the BMI270 instance, it enables BUS_EN and BOOST_EN on the AW9523B and configures the AXP2101 rails to match the official M5Stack CoreS3 initialization.

Configuration.SetPinFunction(12, DeviceFunction.I2C1_DATA);
Configuration.SetPinFunction(11, DeviceFunction.I2C1_CLOCK);

EnableCoreS3InternalBusPower();
EnableCoreS3SensorPower();

I2cConnectionSettings settings = new(1, Bmi270AccelerometerGyroscope.SecondaryI2cAddress);

using (Bmi270AccelerometerGyroscope imu = new(I2cDevice.Create(settings)))
{
    // Enable auxiliary I2C for BMM150
    imu.EnableAuxiliaryI2c(Bmm150.SecondaryI2cAddress);

    // Create BMM150 using the BMI270 aux I2C bridge
    I2cConnectionSettings bmm150Settings = new(1, Bmi270AccelerometerGyroscope.SecondaryI2cAddress);
    using (Bmm150 mag = new(I2cDevice.Create(bmm150Settings), new Bmm150I2cBmi270(Bmm150.SecondaryI2cAddress)))
    {
        while (true)
        {
            var acc = imu.GetAccelerometer();
            var gyr = imu.GetGyroscope();
            var magData = mag.ReadMagnetometer();
            Debug.WriteLine($"Accel: {acc.X:F3} {acc.Y:F3} {acc.Z:F3}");
            Debug.WriteLine($"Gyro:  {gyr.X:F3} {gyr.Y:F3} {gyr.Z:F3}");
            Debug.WriteLine($"Mag:   {magData.X:F3} {magData.Y:F3} {magData.Z:F3}");
            Thread.Sleep(100);
        }
    }
}

M5Stack CoreS3

On the M5Stack CoreS3, the BMI270 is connected to the internal I2C bus at address 0x69 on GPIO12/GPIO11. The BMM150 magnetometer is also on the board, connected through the BMI270's auxiliary I2C interface at address 0x10. M5Stack's official documentation and M5Unified source also show that CoreS3 power routing depends on the AW9523B IO expander and the AXP2101 PMU, which is why the sample enables AW9523 BUS_EN and BOOST_EN and then applies the AXP2101 rail setup before sensor initialization.