The Anatomy of a Mouse!

Week 3:

         The first thing attempted this week for the project on the mechanics side was to try to understand how a wheel mouse works. To do this, an ordinary wheel mouse was taken apart in order to see how the mechanics work and how everything was put together. Below in Figure 1 is a diagram of the components of the mouse labeled with their respective functions. Basically, there is a rubber ball located on the underside of the mouse. The ball is kept in place by a spring that forces the ball against the top and left sides. Because the ball is against these sides, when the mouse is moved, the ball rotates the top and side rods. The top rod is moved when the mouse is moved vertically, and the side rod is moved when the mouse is moved horizontally. The rod then spins the wheels, which are made with little plastic spokes around the edges (seen in Figure 2). There is a light emitter that goes through these spokes and is read by a light detector. The number of times the beam is detected by the light detector is the way that the computer measures how far and how quickly the mouse is being pushed. Besides those main parts of the mouse, there is also a chip that converts the mouse movements into digital signals that can be read by the computer. Towards the top of the mouse are switches that detect the right and left clicks of the mouse.  There is also a scroll wheel in the center. Like all circuit boards, there is a capacitor and resistors (not labeled due to lack of space). Lastly, there are different wires (as of yet, their exact functions are unknown) that connect to a PS/2, which is an outdated connection to the computer. Because of this, a converter to USB is currently being ordered so the mouse can be connected to laptops.

Figure 1: Labeled Diagram of the Components of a Wheel Mouse

Figure 2: Close-Up View of the Wheel along with the LED Emitter and Receptor

http://www.explainthatstuff.com/computermouse.html

        Also, one of the goals of the week for the electrode team was to research how an electrode interface would be implemented. In addition to learning where to place the electrodes on the user, it was also important to find out the magnitude of signal being received from each electrode. That way, there would be a better understanding as to what extent the raw input should be amplified. 

        Below in Figure 3 shows the configuration of the electrodes when placed on the user's face. These electrodes will capture the EOG signals when the user moves their eyes. This signal is produced when light enters the retina, where the light signal is processed into a neural signal.

Figure 3: Sensor Placements for EOG Signals

http://www.waset.org/journals/waset/v31/v31-57.pdf