The EMG Detector is a bridge which connects the human body and electronics. The sensor gathers small muscle signals then processes them with 2th amplifyer and filter. The output signal can then be recognized by Arduino and you can add this signal into your control system. In standby mode, the output voltage is 1.5V. When muscle activity is detected, the output signal rises up to a maximum voltage of 3.3V. So, it can be used with 5V or 3.3V systems.