In this paper, two simple digital signal processor (DSP)-based motor fault signature detection techniques are presented. First, the reference frame theory and its applications to fault diagnosis of electric machinery are introduced. Second, phase sensitive detection (PSD) of motor fault signatures is presented. Both techniques provide very simple and robust way to find the magnitude and phase of the specified fault signatures in the line current. Particularly, PSD has a powerful line current noise suppression capability while detecting the fault signatures. Various faults are experimentally tested both offline using the data acquisition system, and online employing the TMS320F2812 DSP to prove the efficacy of the proposed tools.