A novel magnetic field sensor (MFS) may be created with an organic light emitting diode (OLED) made from an organic semiconductor material and an organic photodetector (OPD) built directly on top (or below) of the OLED, wherein one layer is made from a magnetically isotropic material, and which material has a magneto-resistive or magneto-electroluminescent signal that varies with the magnitude of a magnetic field to allow for measuring only the magnitude of the external magnetic field without regard to magnetic field direction.