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This tutorial assumes you have already installed the QMI8658 library and know how to flash the board. See the library installation guide and getting started guide if needed.

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What is an IMU?

An Inertial Measurement Unit (IMU) is a sensor that measures motion. The QMI8658 on E-Spin is a 6-axis IMU, meaning it provides two types of measurements:
  • Accelerometer (3 axes) — measures proper acceleration, i.e. the force applied to the sensor. At rest flat on a table, it reads ~1g on the Z axis (Earth’s gravity). In free fall, it reads 0g. This lets you determine tilt and detect sudden impacts.
  • Gyroscope (3 axes) — measures angular velocity in degrees per second (°/s). It tells you how fast the sensor is rotating around each axis, not the absolute angle.
Together, they’re the foundation for any motion-aware application: gesture detection, orientation tracking, spin speed measurement, step counting, vibration analysis. The QMI8658 also includes a temperature sensor — useful for compensating sensor drift, since gyroscope bias shifts with temperature. On E-Spin specifically, the IMU is what makes the board aware that it’s spinning. The gyroscope Z-axis is your RPM source. The accelerometer detects taps, drops, and orientation.

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Library

This tutorial uses the QMI8658 Arduino Library by Lahav Gahali, MIT licensed. 
lahavg/QMI8658 @ ^1.0.1
Add to your platformio.ini: 
lib_deps =
    lahavg/QMI8658@^1.0.1

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Wiring

No external wiring needed. The QMI8658 is connected directly to the ESP32-C3 on the PCB. Check your board’s silkscreen or schematic for the exact pin assignment. On current E-Spin hardware:
SignalGPIO
SDA5
SCL4
The I2C address is 0x6A (SA0 low) or 0x6B (SA0 high) — the library auto-detects it.

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Code

#include <Wire.h>
#include <QMI8658.h>

#define SDA_PIN 5
#define SCL_PIN 4

QMI8658 imu;

void setup() {
  Serial.begin(115200);
  while (!Serial) delay(10);

  if (!imu.begin(SDA_PIN, SCL_PIN)) {
    Serial.println("QMI8658 not found. Check wiring and I2C address.");
    while (1) delay(1000);
  }

  Serial.print("QMI8658 detected. Device ID: 0x");
  Serial.println(imu.getWhoAmI(), HEX);  // Should print 0x05

  // Configure ranges
  imu.setAccelRange(QMI8658_ACCEL_RANGE_8G);      // ±8g — enough headroom for taps
  imu.setGyroRange(QMI8658_GYRO_RANGE_2048DPS);   // ±2048 dps — spinner needs this

  // Output data rate: 1000Hz internally, we'll read slower
  imu.setAccelODR(QMI8658_ACCEL_ODR_1000HZ);
  imu.setGyroODR(QMI8658_GYRO_ODR_1000HZ);

  // Set units
  imu.setAccelUnit_mps2(true);   // m/s²
  imu.setGyroUnit_dps(true);     // degrees per second

  imu.enableSensors(QMI8658_ENABLE_ACCEL | QMI8658_ENABLE_GYRO);

  Serial.println("Accel (m/s²) | Gyro (dps) | Temp (°C)");
  Serial.println("-------------------------------------------");
}

void loop() {
  QMI8658_Data data;

  if (imu.readSensorData(data)) {
    Serial.printf("A: %6.2f %6.2f %6.2f | G: %8.2f %8.2f %8.2f | T: %.1f\n",
      data.accelX, data.accelY, data.accelZ,
      data.gyroX,  data.gyroY,  data.gyroZ,
      data.temperature
    );
  }

  delay(50); // ~20Hz print rate
}

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Walkthrough

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What the ranges mean

Accelerometer range controls how large an acceleration the sensor can measure before clipping. ±8g covers normal use — a hard tap registers around 3–5g. If you were mounting this on a drone or rocket, you’d go higher. Gyroscope range is critical for E-Spin. A spinner at 300 RPM rotates at 1800°/s. At 500 RPM that’s 3000°/s, which exceeds ±2048 dps. For very fast spins, this channel will saturate — the fusion filter tutorial addresses this.

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Reading the output

Open the Serial Monitor at 115200 baud. You should see a table like: 
A:  -0.12   0.08   9.82 | G:    0.43   -1.62    0.28 | T: 28.7
A:  -0.11   0.09   9.81 | G:    0.51   -1.55    0.31 | T: 28.7
  • A (accel): at rest flat, Z ≈ 9.81 m/s² (gravity). Tilt the board and the gravity vector redistributes across X/Y/Z.
  • G (gyro): at rest, values should be near zero with a small constant offset called bias — that’s normal and expected. Rotate the board and the relevant axis spikes.
  • T: die temperature in °C. Gyro bias drifts with temperature; the fusion filter tutorial will handle compensation.

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Checking the device ID

imu.getWhoAmI() should return 0x05. If it returns 0x00 or 0xFF, the sensor isn’t responding — run the I2C scanner first to confirm the address and connection.

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Gyro range for spinning

The E-Spin board is designed to spin. Use QMI8658_GYRO_RANGE_2048DPS as your default — lower ranges will saturate and give you flat-topped garbage data the moment you flick it. If you’re only reading at rest (tap detection, orientation), 512DPS gives better resolution.

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What the raw data cannot tell you

Raw gyroscope values give you rotation rate, not angle. Raw accelerometer values give you force, which blends gravity and motion together. Neither alone gives you a clean orientation. To get tilt angles, heading, or quaternions — that’s the next tutorial.

IMU Fusion Filter

Combine accel and gyro with a complementary or Madgwick filter to get stable orientation angles.