A self-powered SECE (synchronized electric charge extraction)-based energy sensor is developed and applied to measuring shaft torque. The design is based on the setup of two-point magnetic plucking allowing the torqueinduced phase angles between two pairs of magnets. The result shows the realization of broadband energy harvesting due to inducing mixed resonant modes of vibration from frequency up-conversion and enhancement by SECE. In addition, torque sensing is achieved by measuring the variation of modal amplitude of voltage response against the phase shift angles. For the case of torque sensing operated at the second resonant mode, the phase angle against the voltage is multi-valued. A solution for the unique sensing is to develop a CNN (convolution neural network) classifier capable of distinguishing various voltage waveforms from different phase angles. The prediction agrees reasonably with experiment.