Input device for disabled persons using expiration and tooth-touch sound signals

This paper presents the realization of an input device for disabled persons, a hands-free man-machine interface using expiration and tooth-touch sound signals. In our research, the expiration signal was detected by a piezo film sensor array and the tooth-touch sound signal by a bone-conduction microphone. The piezo film sensor had two useful effects, piezoelectric and pyroelectric. Utilizing both these effects, we could detect vibration and temperature variation simultaneously. Thus, the duration and strength of expiration could be detected more accurately, minimizing the effect of interference from outside disturbance. The sensors also had added benefits, including being very light weight, small in size and of low-price. The device enabled disabled persons to dramatically extend the number of control channels hands-free by changing the strength and duration of expiration, in conjunction with the tooth-touch sound signal. We developed a novel method for separating the pyroelectric and piezoelectric signals from the original signal. We then designed the device using Hardware Description Language (VHDL) and applied it in a Field Programmable Gate Array (FPGA) chip. We tested our device in a Head Mounted Display (HMD) controller. Finally, we evaluated its performance using the following categories: input error rate, usability and input efficiency compared with a tooth-touch sound alone based input device.