Paper review on Application of Tilt Sensors in HumanComputer Mouse Interface for People With Disabilities by Yu-Luen Chen, Associate Member, IEEEThe paper describes an economical and easy method to design head controlled mouse for specially abled people. A hardware model is proposed for this purpose. It consists of tilt sensors, Intel 8951 microprocessor, a 2:1 Multiplexer and touch switches.The hardware consist of a headset on which two tilt sensors mounted - one tilt sensor detects the left-right displacement of the head while the other detects the horizontal and vertical displacement of head. The tilt sensors are placed on the frontal and lateral side of the headset. According to the motion sensed by the tilt sensors, the movement of cursor on the PC is done. The touch button is placed close to cheek. The purpose of this touch button is to provide the function of single and double click to the user. User can perform the clicking action by their cheek puffs.

Figure 1: The block diagram representation of the tilt sensors-controlled computer mouse interface

A block diagram of the head controlled mouse is shown above. The circuit comprises of three major elements: 1) tilt sensors 2) signal conditioning module 3) controller (Intel-8951 processor). The tilt sensor senses the motion of the users head, the output of which is analog voltage. The analog output is then amplified and then passed to the low pass filter in the signal conditioning circuit. The analog voltage from the signal conditioning circuit is then fed to Analog to Digital Converter. A 2:1 multiplexer is used to multiplex the outputs of ADC and feed it as input to the processor ports Port1 and Port 2. The touch switches (attached to Port 2) placed near the cheeks trigger signals for the clicking of mouse. Port 3 transmits these signals to PC using RS-232 protocol. Application Program written in Visual Basic API reads the command sent by serial port.

Advantages and Disadvantages:The system is cheap and useful for people with severe disabilities. The data rate is slow due to RS 232 protocol. Hence the response of the mouse to the head movement may be slower. Also, the system uses tilt sensor (with tilt angle of 45) which are although cheaper than accelerometers, but are able to detect tilt only exceeding threshold angle. Intel 8951 processor is used which is slower in execution of instruction as compared to its contemporary controllers like AVR, PIC, ARM etc.Points not understood:1) Why MUX was used in the hardware.2) How the driver for the mouse was designed?