  We demonstrate a fully automated open-source magnetometer designed primarily
for characterization of magnetic fields produced by coils, permanent magnets or
by parasitic sources. It is based on an Arduino Mega microcontroller and a
three-axis Hall sensor with a measurement range of +/-8 G per axis and the RMS
of the field readout below 0.3 mG. For all practical purposes, the sensor
displacement during data acquisition is virtually unlimited, which can be
particularly useful for characterizing large or extended coils like Helmholtz
cages or Zeeman slowers. All components needed for the construction are cheap
and widely available off-the-shelf elements or are 3D-printed. The operation of
the magnetometer is controlled via a graphical user interface (GUI), which
manages all essential functionalities, like data acquisition and plotting. The
GUI also incorporates additional features, like data averaging, calibration of
the displacement of the Hall sensor or real-time readout of the magnetic field,
useful for monitoring magnetic field changes. We have used a pair of
rectangular coils constructed for a potassium--cesium 2D magneto-optical trap
to benchmark the performance of the magnetometer. We have obtained good
agreement with both simulations and measurements acquired with a commercial
gaussmeter.
