According to some embodiments, a motion tracker device can include a substrate and a plurality of light-direction detectors mounted on the substrate. Each light-direction detector may be configured to: detect, at two optically isolated points, the intensity of a light from a light source； generate a current signal representing the photodiode differential and proportional to the intensity of the light； and transmit the current signal to a computing device. Each of the plurality of light-direction detectors can be mounted on the substrate at an angle selected such that the computing device can use the transmitted signal to determine the motion of a motion tracker with six degrees of freedom.
