Interfacing HMC5883L Magnetometer with Raspberry Pi

Overview

In this tutorial, we will explore how to connect the HMC5883L Triple Axis Digital Magnetometer to a Raspberry Pi and harness its capabilities using Python. The HMC5883L stands out as an optimal choice for digital compass applications, thanks to its three-dimensional magnetometer features that allow for precise measurements of magnetic field strength and orientation. This makes it an invaluable tool for pinpointing the Earth’s magnetic north.

Upon integrating the HMC5883L magnetometer with the Raspberry Pi, we will be able to fetch compass readings and ascertain the magnetic field across the X, Y, and Z axes in terms of microteslas (µT). From this data, determining the heading in degrees becomes a straightforward computation. We’ll be guiding you through every step of the process, ensuring you can seamlessly execute these tasks with Python on your Raspberry Pi.

Bill of Materials

We need following components to work on this project.

S.N.	Components	Quantity	Purchase Link
1	Raspberry Pi 4	1	Amazon \| AliExpress \| SunFounder
2	HMC5883L Magnetometer	1	Amazon \| AliExpress \| SunFounder
3	Jumper Wires	10	Amazon \| AliExpress \| SunFounder
4	Breadboard	1	Amazon \| AliExpress \| SunFounder

HMC5883L 3-Axis Compass/Magnetometer

The HMC5883L is a digital compass conceived by Honeywell. It is a surface-mount, multi-chip module engineered specifically for the detection of low magnetic fields. It is particularly adept at supplying directional data, making it a common choice for navigation and positioning systems.

The design of the HMC5883L revolves around anisotropic magnetoresistive (AMR) technology, which facilitates the precise measurement of magnetic fields. It includes three-axis sensors, with field capacities spanning from ±1.3 to ±8.1 Gauss. This denotes its capability to measure magnetic fields across three distinct axes (X, Y, and Z), allowing it to sense the direction of the Earth’s magnetic field in a three-dimensional context.

The HMC5883L is equipped with numerous inherent features that simplify its incorporation into a variety of systems. Among these are an integrated ADC (Analog-to-Digital Converter) offering 12-bit data output, and an I2C serial bus interface. This interface is utilized for device communication, enabling it to transfer data to a microcontroller or another processing unit.

The HMC5883L Magnetometer Module is comprised of an HMC5883L Magnetometer IC, a Voltage Regulator IC, resistors, and capacitors, all consolidated within an integrated circuit. It uses a voltage regulator IC XC6206P332MR (662K).

Refer to HMC5883L datsheets to learn more: Download HMC5883L Datasheet

Specifications of HMC5883L

Operating Voltage: 3V to 6V DC
Operating Current: 100-130 μA
I2C interface
1-2 degree heading accuracy
Integrated 12-bit ADC
160Hz max data rate
Range of -8 to +8 Gauss
Data Output Rate: 0.75, 1.5, 3, 7.5, 15 Hz

Pinout of HMC5883L

The HMC5883L module has five pins as shown in this image below:

Here is a basic description of the typical pinout for an HMC5883L module.

VCC: This is the power supply pin. It requires a DC voltage, typically 3V -6V.
GND: This is the ground pin.
SCL: This is the clock line for the I2C interface.
SDA: This is the data line for the I2C interface.
DRDY: This is Data Ready pin which goes low when new data is available. It’s optional and isn’t always used in basic applications.

Register Mapping & I2C Communication

Register Address	Name	Access
00	Configuration Register A	Read/Write
01	Configuration Register B	Read/Write
02	Mode Register	Read/Write
03	Data Output X MSB Register	Read
04	Data Output X LSB Register	Read
05	Data Output Z MSB Register	Read
06	Data Output Z LSB Register	Read
07	Data Output Y MSB Register	Read
08	Data Output Y LSB Register	Read
09	Status Register	Read
10	Identification Register A	Read
11	Identification Register B	Read
12	Identification Register C	Read

The HMC5883L magnetometer uses various internal registers to configure and receive data:

Configuration Register A (0x00): Configures device operation, including output data rate and measurement configuration.
Configuration Register B (0x01): Sets the device gain and sensitivity.
Mode Register (0x02): Selects the operating mode, such as continuous measurement, single measurement, or idle mode.
Data Output X Registers (0x03 and 0x04): Hold X-axis sensor readings.
Data Output Y Registers (0x05 and 0x06): Hold Y-axis sensor readings.
Data Output Z Registers (0x07 and 0x08): Hold Z-axis sensor readings.
Status Register (0x09): Contains status flags about data output.
Identification Registers (0x0A, 0x0B, 0x0C): Used to identify the device.

The HMC5883L employs the I2C communication protocol, functioning as a slave device. Its designated I2C device address is 0x1E. The corresponding addresses for its read and write operations are as follows:

For write operations (SLA+W), the address is 0x3C.
For read operations (SLA+R), the address is 0x3D.

Interfacing HMC5883L Magnetometer with Raspberry Pi Pico

Let us interface the HMC5883L Magnetometer with Raspberry Pi 4 using Python code and extract magnetometer readings for the X, Y, and Z axes, as well as the heading information.

The connection diagram is straightforward.

Connect the VCC & GND pin of the HMC5883L magnetometer to the 3.3V & GND pin of the Raspberry Pi. Likewise, join the SDA & SCL pins of the Magnetometer to the SDA (GPIO2) & SCL (GPIO3) pins of the Raspberry Pi respectively.

Setting Up the Raspberry Pi

Before moving directly to the Python programming part, we need to setup the Raspberry Pi.

1. Enable I2C on the Raspberry Pi:

Open a terminal and type sudo raspi-config.
Navigate to Interfacing Options > I2C and enable it.
Reboot the Raspberry Pi.

2. Install the necessary Python packages:

1 2	sudo apt-get update sudo apt-get install i2c-tools python3-smbus

3. Detect the device:
After connecting the HMC5883L, you can detect it using the following command:

1	i2cdetect -y 1

If everything is connected properly, you should see an address 1E appear in the list, which is the default address for the HMC5883L.

Python Code for Interfacing HMC5883L with Raspberry Pi

Here is a Python Code to interface HC5883L Magnetometer with Raspberry Pi 4. Copy the following code and paste it on your Thonny IDE. Then Save it with any name.

This simple Python script will read data from the HMC5883L.

import smbus

import time

import math

# HMC5883L register addresses

ADDRESS = 0x1E

CONFIG_A = 0x00

CONFIG_B = 0x01

MODE = 0x02

X_MSB = 0x03

Z_MSB = 0x05

Y_MSB = 0x07

bus = smbus.SMBus(1)

def setup():

bus.write_byte_data(ADDRESS, CONFIG_A, 0x70) # Set to 8 samples @ 15Hz

bus.write_byte_data(ADDRESS, CONFIG_B, 0x20) # 1.3 gain LSb / Gauss 1090 (default)

bus.write_byte_data(ADDRESS, MODE, 0x00) # Continuous measurement mode

def read_raw_data(addr):

# Read raw 16-bit value

high = bus.read_byte_data(ADDRESS, addr)

low = bus.read_byte_data(ADDRESS, addr+1)

# Combine them to get a 16-bit value

value = (high << 8) + low

if value > 32768: # Adjust for 2's complement

value = value - 65536

return value

def compute_heading(x, y):

# Calculate heading in radians

heading_rad = math.atan2(y, x)

# Adjust for declination angle (e.g. 0.22 for ~13 degrees)

declination_angle = 0.22

heading_rad += declination_angle

# Correct for when signs are reversed.

if heading_rad < 0:

heading_rad += 2 * math.pi

# Check for wrap due to addition of declination.

if heading_rad > 2 * math.pi:

heading_rad -= 2 * math.pi

# Convert radians to degrees for readability.

heading_deg = heading_rad * (180.0 / math.pi)

return heading_deg

def main():

setup()

while True:

x = read_raw_data(X_MSB)

y = read_raw_data(Y_MSB)

z = read_raw_data(Z_MSB)

heading = compute_heading(x, y)

print(f"X: {x} uT, Y: {y} uT, Z: {z} uT, Heading: {heading:.2f}°")

time.sleep(0.5)

if __name__ == "__main__":

main()

This script initializes the HMC5883L in continuous measurement mode and then continuously reads and prints the X, Y, and Z magnetometer values. The data might need to be calibrated or adjusted depending on your application and surrounding magnetic fields.

To calculate the heading (or the orientation in degrees) using the magnetometer values, one usually makes use of the arctangent function. The heading can be determined from the X and Y magnetometer readings.

Testing & Results

You may run the above Python Script and the Thonny Shell will start showing the Magnetometer readings in micro-Tesla and Heading angles in degrees.

To observe the change in magnetic field values, bring any magnetic material or magnet near the sensor. You will observe drastic change in the magnetic field readings. The heading angle can be varied simly by rotating the sensor.

Remember, the computed heading will be relative to the Earth’s magnetic North and not the true North. This distinction is important if you are navigating based on the heading.

The difference between the magnetic North and the true North is known as the magnetic declination, and it varies depending on your geographic location. You might need to adjust the heading for magnetic declination based on where you’re located.