How to Use gy_91: Examples, Pinouts, and Specs

The GY-91 is a compact sensor module manufactured by InvenSense, combining the MPU9250 (a 9-axis motion tracking device) and the BMP280 (a precision barometric pressure sensor). This module integrates a 3-axis accelerometer, 3-axis gyroscope, 3-axis magnetometer, and a barometric pressure sensor, making it ideal for applications requiring motion tracking, orientation sensing, and altitude measurement.

• Robotics and autonomous vehicles
• Drones and UAVs for stabilization and navigation
• Mobile devices for motion and orientation sensing
• Wearable devices and fitness trackers
• Weather stations and altitude measurement systems

1. Power the Module: Connect the VCC pin to a 3.3V or 5V power source and GND to ground.
2. Connect Communication Lines:
   • For I2C: Connect the SCL and SDA pins to the corresponding I2C pins on your microcontroller.
   • For SPI: Connect the SCL, SDA, and CS pins to the SPI clock, data, and chip select pins, respectively.
3. Pull-Up Resistors: Ensure pull-up resistors (typically 4.7kΩ) are present on the I2C lines if not already included on the module.
4. Initialize the Sensor: Use appropriate libraries or write custom code to initialize and configure the MPU9250 and BMP280.

• Voltage Compatibility: Ensure your microcontroller's I2C or SPI pins are compatible with the GY-91's voltage levels (3.3V or 5V).
• Magnetometer Calibration: Perform a magnetometer calibration to ensure accurate heading measurements.
• Mounting Orientation: Mount the module securely and in the correct orientation for accurate motion and orientation sensing.
• Noise Filtering: Use software filters to reduce noise in accelerometer and gyroscope readings.

Below is an example of how to interface the GY-91 with an Arduino UNO using the I2C protocol. This code uses the Adafruit_Sensor and Adafruit_BMP280 libraries for the BMP280 and the MPU9250 library for the MPU9250.

#include <Wire.h>
#include <Adafruit_Sensor.h>
#include <Adafruit_BMP280.h>
#include <MPU9250.h>

// Create instances for the sensors
Adafruit_BMP280 bmp; // BMP280 instance
MPU9250 mpu(Wire, 0x68); // MPU9250 instance with I2C address 0x68

void setup() {
  Serial.begin(9600);
  Wire.begin();

  // Initialize BMP280
  if (!bmp.begin(0x76)) { // Default I2C address for BMP280 is 0x76
    Serial.println("BMP280 initialization failed!");
    while (1);
  }
  Serial.println("BMP280 initialized successfully.");

  // Initialize MPU9250
  if (mpu.begin() != 0) {
    Serial.println("MPU9250 initialization failed!");
    while (1);
  }
  Serial.println("MPU9250 initialized successfully.");
}

void loop() {
  // Read BMP280 data
  float temperature = bmp.readTemperature();
  float pressure = bmp.readPressure();
  float altitude = bmp.readAltitude(1013.25); // Sea level pressure in hPa

  // Read MPU9250 data
  mpu.readSensor();
  float accelX = mpu.getAccelX_mss();
  float accelY = mpu.getAccelY_mss();
  float accelZ = mpu.getAccelZ_mss();
  float gyroX = mpu.getGyroX_rads();
  float gyroY = mpu.getGyroY_rads();
  float gyroZ = mpu.getGyroZ_rads();
  float magX = mpu.getMagX_uT();
  float magY = mpu.getMagY_uT();
  float magZ = mpu.getMagZ_uT();

  // Print sensor data
  Serial.print("Temperature: "); Serial.print(temperature); Serial.println(" °C");
  Serial.print("Pressure: "); Serial.print(pressure); Serial.println(" Pa");
  Serial.print("Altitude: "); Serial.print(altitude); Serial.println(" m");
  Serial.print("Accel (X, Y, Z): "); 
  Serial.print(accelX); Serial.print(", ");
  Serial.print(accelY); Serial.print(", ");
  Serial.println(accelZ);
  Serial.print("Gyro (X, Y, Z): "); 
  Serial.print(gyroX); Serial.print(", ");
  Serial.print(gyroY); Serial.print(", ");
  Serial.println(gyroZ);
  Serial.print("Mag (X, Y, Z): "); 
  Serial.print(magX); Serial.print(", ");
  Serial.print(magY); Serial.print(", ");
  Serial.println(magZ);

  delay(1000); // Wait 1 second before the next reading
}

1. Sensor Not Detected:

   • Ensure the I2C or SPI connections are correct.
   • Verify the I2C address (default is 0x68 for MPU9250 and 0x76 for BMP280).
   • Check for proper power supply (3.3V or 5V).

2. Inaccurate Readings:

   • Perform calibration for the accelerometer, gyroscope, and magnetometer.
   • Ensure the module is mounted securely and free from vibrations.

3. Communication Errors:

   • Check for loose or incorrect wiring.
   • Ensure pull-up resistors are present on the I2C lines.

• Use a logic level shifter if your microcontroller operates at 5V and the GY-91 is running at 3.3V.
• For better accuracy, use software libraries that support sensor fusion algorithms (e.g., Madgwick or Mahony filters).
• Avoid placing the module near magnetic or electrical interference sources.