Thesis - Teknisk Design

uncoated one, so the capacitance of each corner of the layer depends on thedistance to the conductor (the finger), the nearer, the larger change incapacitance. This property is used to calculate the finger position on the touchscreen. This property works as long as there is just one finger or conductor touchingthe touch screen, meaning that this technology does not allow multitouching. It issaid to suffer from parasitic capacitance coupling and it needs calibration duringmanufacture. The strongest fact of this type of capacitive touch screen is thelongevity of its lifespan due to the lack of moving parts (Tyco Electronics Corporation2011).Projected capacitanceThe technology is also based in the creation of dynamic capacitor by touching aresistive material someway charged; the main difference is that the layer is not allcoated in the back. An x-y grid of electrodes creates the conductive layer with acontrol in each row and column or in each intersection protected by a glass layer ontop. The exact position of the conductor is measured by the change in capacitancecreated by a conductor touching the glass surface; there is no need of directcontact. The possibility of having many resistive layers between the grid and thetouching conductor enables to have protective insulating layers and screenprotectors that lengthen lifespan. Weather and vandal-proof glasses turns projectedcapacitance touch screen into a perfect device for outdoors conditions. There is aweakness that might be stressed, conductive smudges and similar interferences caninterfere with the good performance of this touch screens. Depending on theimplementation of the device, it could work with glove hands and with stylus, a reallynecessary fact if you need signature capture. There are two types of PCT, where themain different is based on the position of the capacitors allowing or not to havemultiple-touch (Tyco Electronics Corporation 2011).Self capacitanceConsidering capacitor positioning in self-capacitance there is independence inoperability between columns and rows. This means that for each row and for eachcolumn of electrodes a different current meter measures the capacity load. Thisdisposition does not allow having multiple-touch and it suffers from “ghosting” andmisplaces location sensing when more than one finger is touching it (Barrett, G. L.And Omote, R. 2010).Mutual capacitanceIn relation to the number of capacitors in a mutual capacitance touch screen incomparison to a self-capacitance touch screen there are much more in the firsttype. The reason why is that their disposition is in each intersection between acolumn and a row. That means that for a square touch screen with five columns andfive rows there will be ten capacitors for a Self capacitance touch screen andtwenty-five for a Mutual capacitance touch screen.The measurement of dynamic capacitance moves from the corners to eachinteraction between row and column. That makes the measurement more accurateand does not suffer from ghosting as self-capacitance touch screens. It allows multitouchoperation so different fingers and stylus could be tracked at the same time.11