Abstract: According to the requirement of pre-multi frequency eddy current testing method, pre-multi-frequency excitation source was developed by using AVR microcontroller plus DAC. According to the requirements of the time-sharing, multiple frequencies could be outputted with each frequency without interference between the transition. A continuous single frequency excitation signal for impedance analysis could be outputted as well. With the microcontroller, the demodulated signal benchmark could be produced. Using computer-aided programming method, the waveform data files for use by the microcontroller were automatically generated, with reducing the input of microcontroller development process of the code. Automatic sorting equipment has been successfully applied to production by using the excitation signal source.