HMC5883L is a 3-axis magnetometer which is used for measuring the direction and magnitude of the Earth’s magnetic field. It is used for low cost compassing and magnetometry.
It measures the Earth’s magnetic field value along the X, Y, and Z axes from milli-gauss to 8 gauss.
It can be used to find the direction of the heading of the device.
It uses the I2C protocol for communication with the microcontroller.
For more information about Magnetometer HMC5883L and how to use it, refer to the topic HMC5883L Magnetometer Module in the sensors and modules section.
A NodeMCU can communicate with this module using the I2C communication protocol. To know more about I2C functions in NodeMCU refer to NodeMCU I2C with ESPlorer IDE or NodeMCU I2C with Arduino IDE