Touch Screen Technology Comparison
Projected Capacitive
In the short time since the introduction of projected capacitive touch screens in iPhones, a myriad of construction methods have been developed. All projected capacitive designs have two key features in common - the sensing mechanism (ITO layer) that lies behind the touch surface and the use of no moving parts. The most common design incorporates the simple concept shown below.
In many applications, especially portable devices, the construction is similar to that of the iPhone:
- Cover Glass
Chemically strengthened with holes and slots cut into it, either 0.75mm or 1.1mm thick.
- Indium Tin Oxide (ITO)
Deposited onto the top side of a piece of glass, with molybdenum/aluminum/molybdenum signal lines at the edge.
- Indium Tin Oxide (ITO)
Deposited onto bottom side of glass, with molybdenum/aluminum/molybdenum signal lines at the edge.
Advantages
- Extremely Durable
- Easy to Use
- Highly Accurate
- Exceedingly Reliable
- Advanced Functionality
- Operates in Environmental Extremes
- Works with Finger, Gloves and Active Stylus
Resistive
The sensor consists of a piece of glass with a conductive coating on top, plus a polyester top sheet with a conductive coating on the bottom. The conductive surfaces are held apart by “spacer dots”, usually glass beads that are silk-screened onto the coated glass. On a 5-wire design (the most commonly used type of resistive in large screen POS applications); a voltage is applied to the 4 corners of the glass layer. When a person presses on the top sheet, it is deformed and its conductive side comes in contact with the conductive side of the glass, effectively closing a circuit. The voltage at the point of contact is read from a wire connected to the top sheet.
Advantages
- Can be activated with any device
- Low cost solution
- Low power consumption
- Disadvantages
- Less durability compared to other technologies
- Less transmittance and overall optical quality
- Requires periodic recalibration
Surface Capacitive
The capacitive sensor has a conductive coating on the front surface with wires connected to each corner. A small voltage is applied to each of these 4 corners. The operation relies on the capacitance of the human body. When a person touches the screen, a small current flows to the point of touch, causing a voltage drop which is sensed at the 4 corners.
Advantages
- More durable than resistive (because the top layer is not plastic
- Higher transmittance than resistive (fewer layers
Disadvantages
- Accepts input from finger only (or a special, tethered conductive stylus
- Susceptible to electromagnetic interference can cause an erratic cursor location
- Accuracy is dependent on capacitance of person touching the display
- Requires periodic calibration
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