Noise & Resolution

Noise sets how steady your heading is. The Earth’s field is weak (around 0.5 G), so a sensor with 0.4 mG noise holds a sub-degree heading while a 2 to 4 mG part will wander a little. More ADC bits only help if the noise floor is low enough to use them.

Full-Scale Range

A pure compass only needs about ±1 to ±2 G. Wider ranges (±8 G, ±16 G or more) stop the sensor saturating next to motors, magnets or speakers, and let you measure nearby magnets for position sensing. Selectable ranges give you both.

Set/Reset & Offset Stability

AMR sensors can be magnetised by a strong field and drift. Parts with a built-in SET/RESET strap (MMC5983MA, QMC5883L, HMC5883L) can degauss themselves and cancel offset and temperature drift, which keeps calibration valid for longer.

Interface & Voltage

I2C is easiest; SPI is faster and avoids address clashes. Check the board, not just the chip: GY-271/GY-273 and Waveshare boards accept 3.3V or 5V, while bare LIS3MDL, MMC5983MA and RM3100 boards are 3.3V only and need a level shifter on a 5V Arduino.

Standalone vs IMU / Fusion

A standalone magnetometer gives raw field data. A 9-axis IMU adds accelerometer and gyro for tilt compensation, and a fusion chip like the BNO055 does the maths for you and outputs heading directly. Pick based on how much firmware you want to write.

A bare magnetometer only gives a correct heading while it sits flat. The Bosch BNO055 fixes that by combining a magnetometer, accelerometer and gyroscope with an onboard ARM Cortex-M0 that runs Bosch’s sensor-fusion firmware. Instead of raw field values, it hands you a tilt-compensated compass heading, Euler angles and quaternions over I2C or UART, and it calibrates itself in the background as you move it. Adafruit’s breakout adds a regulator and level shifting for 3V or 5V boards and has one of the best-maintained Arduino and CircuitPython libraries around. It is the fastest path from “wires on a breadboard” to “my rover knows which way it is pointing” on a moving, tilting platform.

The RM3100 uses PNI Sensor’s magneto-inductive coils (the 13101/13104 sensor set plus the 13156 controller ASIC, as listed) rather than AMR or Hall elements. The result is a sensor with roughly 13 nT resolution, very low noise, no hysteresis and excellent temperature stability, which is why you find it in survey equipment, high-end drone GPS/compass units and magnetic anomaly projects. You trade off sample rate against resolution by setting the cycle count, so it can go from ultra-precise to a few hundred hertz. It is an SPI, 3.3V-only module with no regulator, the library ecosystem is thinner than the others, and this listing is a generic-brand board, so plan on reading the datasheet. For lab-grade field measurements, nothing else here comes close.

ST’s LIS3MDL is the magnetometer inside many commercial IMU boards, and the CJMCU breakout gives you the bare chip cheaply. Its standout feature is a selectable range up to ±16 G, so it will not saturate when mounted close to motors or when you deliberately track a nearby magnet, plus a fast mode that pushes output data up to about 1 kHz. Both I2C and SPI are broken out, and the Adafruit LIS3MDL library works with it unchanged. Be careful with power: the listing confirms a 1.9 to 3.6V supply, so feed it from 3.3V and level-shift the I2C lines on a 5V Uno. Its noise is higher than the MMC5983MA, so it is better at robust, wide-range sensing than at a rock-steady sub-degree compass.

The Bosch BMM150 is the geomagnetic sensor Bosch designed for phones and wearables, and it is the same magnetometer core used inside the BNO055. That heritage shows in its very low current draw and its preset power modes, which makes it the natural choice for battery-powered compasses, BLE beacons and ESP32 projects that spend most of their time asleep. Waveshare’s board is a proper branded module with an onboard voltage translator, so it is safe on both 3.3V and 5V boards, and it ships with I2C by default and SPI selectable via a resistor. Waveshare also provides Arduino, Raspberry Pi and STM32 demo code, which saves real time.

If you were going to buy an MPU-9250, buy the ICM-20948 instead. TDK InvenSense’s replacement for the discontinued MPU-9250 packs a 3-axis gyro, 3-axis accelerometer and an AK09916 magnetometer with ±4900 µT range into one low-power package, rated at about 2.5 mW for all nine axes. One board gives you everything needed for tilt-compensated heading or a full Madgwick/Mahony AHRS filter, and the onboard Digital Motion Processor can offload fusion if you use the SparkFun library. The magnetometer sits behind the IMU’s auxiliary I2C bus, so reading it takes a little more setup than a standalone chip, and its resolution (0.15 µT per LSB) is modest. Treat it as an IMU first and a compass second.

The Honeywell HMC5883L is the sensor behind thousands of older Arduino compass tutorials, including our own HMC5883L with Arduino guide. It offers eight selectable ranges from ±0.88 to ±8.1 G, a 12-bit ADC and 1 to 2 degree heading accuracy, and it answers at I2C address 0x1E. Honeywell discontinued it, so this Comimark 2-pack is listed as GY-273 HMC5883L, but be realistic: across the market many boards sold under this name now carry the QMC5883L. Run an I2C scanner as soon as it arrives. If it shows 0x1E, the classic Adafruit HMC5883 library and old tutorials work as-is; if it shows 0x0D, switch to a QMC5883L library. For new designs, the GY-271 QMC5883L above is the safer buy.

Want the steadiest compass heading?

Get the SparkFun MMC5983MA: 0.4 mG noise and SET/RESET drift cancellation for sub-degree heading.

Learning on a budget?

The GY-271 QMC5883L works on 3.3V or 5V and costs almost nothing. Use a QMC5883L library.

Rover, boat or drone that tilts?

The Adafruit BNO055 outputs a fused, tilt-compensated heading with no filter code to write.

Science or field mapping?

The RM3100 gives nanotesla-level resolution with no hysteresis. Expect 3.3V SPI and datasheet work.

Running on a coin cell or LiPo?

The Waveshare BMM150 has Bosch’s low-power modes and a level-shifted 3.3V/5V board.

Building a full AHRS / IMU?

The ICM-20948 puts gyro, accel and mag in one chip. For noisy, motor-heavy enclosures, the LIS3MDL‘s ±16 G range resists saturation.

What is the difference between the HMC5883L and the QMC5883L?

They share the same board footprint (GY-271 / GY-273) but are different chips. The Honeywell HMC5883L uses I2C address 0x1E and a 12-bit ADC; it is discontinued. The QST QMC5883L uses address 0x0D, a 16-bit ADC and a completely different register map, so HMC5883L code returns zeros or garbage on it. Run an I2C scanner sketch: 0x1E means HMC5883L, 0x0D means QMC5883L. Then pick the matching library. Nearly every budget board sold today is a QMC5883L.

Why is my compass heading wrong, and how do I calibrate it?

Almost always it is hard-iron and soft-iron distortion from things mounted near the sensor: motors, batteries, steel screws, speakers and wires carrying current. Calibrate with the sensor installed in its final position. Slowly rotate the whole device through every orientation (a figure-eight motion works) while logging min and max values on each axis. Subtract the midpoint of each axis to remove hard-iron offsets and scale the axes so they match to correct simple soft-iron effects. Tools like MotionCal or Magneto compute a full ellipsoid fit if you need more accuracy. Re-calibrate whenever you change the hardware around the sensor.

Do I need tilt compensation?

Only if the sensor does not stay level. The simple atan2(Y, X) heading assumes the board is flat; tilt it by 10 or 15 degrees and the heading can be off by tens of degrees, because the Earth’s field points steeply downward at most latitudes. For anything handheld, flying, floating or driving over rough ground, add an accelerometer to measure pitch and roll and rotate the magnetometer vector back into the horizontal plane, or use a fusion device like the BNO055 or ICM-20948 that does it for you.

Does a magnetometer point to true north?

No, it points to magnetic north. The angle between magnetic north and true (geographic) north is the magnetic declination, which ranges from near zero to more than 20 degrees depending on where you are, and it changes slowly over the years. Look up your local value from the NOAA or BGS magnetic-field calculator and add it to your heading in code. If your project has GPS, you can compute declination automatically from your coordinates with a world magnetic model library.

Can I connect these modules to a 5V Arduino Uno?

Some, yes. The GY-271 QMC5883L, GY-273 HMC5883L, Waveshare BMM150 and Adafruit BNO055 boards include regulators or level translators and accept 5V. The CJMCU LIS3MDL, SparkFun MMC5983MA and RM3100 boards are 3.3V only: power them from 3.3V and put a bidirectional level shifter (or a Qwiic shield for the SparkFun board) on the I2C or SPI lines. On ESP32, Raspberry Pi Pico and Raspberry Pi, which are 3.3V natively, every module here connects directly.