Nine axes on an Arduino Uno

// Nine axes: an LSM6DSOX accelerometer and gyroscope with an LIS3MDL
// magnetometer beside it, the three sensors a drone or a head tracker
// needs: which way is down, how fast it turns, and which way is north.
//
//   LSM6DSOX   SDA -> SDA   SCL -> SCL
//   LIS3MDL    SDA -> A4    SCL -> A5
//
// Pitch comes from the accelerometer alone; the gyroscope reads the turn
// rate only while the board is moving.
//
// Things to try. Drag the pitch slider on the LSM6DSOX. Drag the heading
// slider on the LIS3MDL, and the one on the LSM6DSOX to see the gyro move.

#include <Adafruit_LSM6DSOX.h>
#include <Adafruit_LIS3MDL.h>

Adafruit_LSM6DSOX imu;
Adafruit_LIS3MDL mag;

void setup() {
  Serial.begin(9600);
  if (!imu.begin_I2C()) {
    Serial.println("No LSM6DSOX");
  }
  if (!mag.begin_I2C()) {
    Serial.println("No LIS3MDL");
  }
  Serial.println("Nine axes");
}

void loop() {
  delay(100);
  float ax, ay, az, gx, gy, gz;
  imu.readAcceleration(ax, ay, az);
  imu.readGyroscope(gx, gy, gz);
  sensors_event_t field;
  mag.getEvent(&field);
  float pitch = atan2(-ax, az) * 180 / PI;
  float heading = atan2(field.magnetic.y, field.magnetic.x) * 180 / PI;
  if (heading < 0) heading += 360;
  Serial.print("pitch ");
  Serial.print(pitch, 0);
  Serial.print("  turn ");
  Serial.print(gz, 0);
  Serial.print(" dps  heading ");
  Serial.println(heading, 0);
  delay(200);
}