Rhythmic motor behavior has been associated with phase dependent patterns of brain oscillations; however, causality in this relationship can only be determined through demonstration of the impact of direct modulation of brain oscillations on motor behavior. This project looks to determine the direct implications of brain stimulation on motor function, using transcranial alternating current stimulation (tACS) to modulate oscillatory brain activity in phase dependent manner with respect to rhythmic motor behavior. However, no commercial system to synchronize tACS and motor behavior is available. We report on the development of a system to do so, and provide validation results. System components include a commercial tACS system, a high precision load cell, a data acquisition card, and custom software developed in Matlab. A user interface was designed to present a sinusoidal wave to be traced by applying finger force on the load cell inducing a rhythmic motor pattern. Critically, the system is designed to manipulate the synchronization between the force target and tACS waveform applied to the brain in order to precisely align (or misalign) the two oscillatory patterns. Validation of the synchronization was tested by examining the phase difference between the force target and the tACS when programmed for zero-phase difference, at different frequencies. Phase offsets at .4 Hz (.04_.02 radians), .6 Hz (.13_.01 radians), .8 Hz (.16_.01 radians), 1 Hz (.06_.03 radians) indicate sufficient synchronization between the two signals. Based on the technical validation data presented here we are now prepared to begin data collection.