This work focuses on the diagnosis of energy consumption of commonly used microcontrollers with various driving clock-frequency. The interaction among the driving clock-frequency, processing time and current consumption are determined to be a guidance for the design of low-power wireless sensor applications. In implementation, the microcontrollers are supposed to process the data following the operational procedures of wireless sensor application, which is programmed to solve mathematical equation with various driving clock-frequencies, and then sleep to reduce the power consumption. With a single circle procession, the current consumption at each driving clock-frequency are captured and analyzed. As the results, the current consumption is proportional to the driving clock-frequency, however energy consumption is minimized at highest clock-frequency.