Sensing weak magnetic fields is a topic of great importance in basic science and technology due to its wide range of applications. In this context, solid-state and nanoscale quantum sensors are poised to revolutionize the sensing platforms due to their ultimate sensitivity, precision, and robustness. The sensitivity comes from the central weakness of quantum systems: their strong sensitivity to external disturbances. Very high precision is provided by these atom-like quantum systems as they are defined by natural constants which are inherently free of fabrication tolerance. Moreover, the protected environment of atoms offers a higher resilience against external influences as compared to artificially designed structures.

Recently, considerable attention has been paid to color centers in diamonds for their applications in spin-based quantum sensing and quantum information processing. Among them, the nitrogen vacancy (NV) center is of particular interest since it possesses a non-zero spin in its ground state and is compatible with optical methods to initiate and read out this spin. The NV center is a defect in the crystal lattice of a diamond where two adjacent carbon atoms are replaced by a nitrogen atom and a vacancy. It provides a wide range of applications including electric-field, magnetic-field, pressure, and temperature sensing, as well as nanoscale NMR.

This thesis focuses on the development of software and hardware aiming to facilitate the use of diamond nitrogen-vacancy (NV) color centers as high-precision magnetic field sensors, through the technique of optically detected magnetic resonance (ODMR). The thesis explains the main principles and concepts of ODMR, as well as the hardware and software considerations for continuous and pulsed ODMR experiments. An emphasis is put on developing open-source code and making it compatible with affordable hardware, so as to democratize ODMR experiments and applications. In the last chapters, the thesis also presents solutions for enhancing the magnetic field sensitivity of the NV center through an efficient collection, excitation, and manipulation of NV electron spins.