Touch Screen Technology Comparison

In the short time since the introduction of projected capacitive touch screens in the iPhone, a myriad of construction methods have been developed. All projected capacitive touch screen 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.

Mutual capacitance is now the more common projected capacitive approach and makes use of the fact that most conductive objects are able to hold a charge if they are very close together. If another conductive object, in this case a finger, bridges the gap, the charge field is interrupted and detected by the microcontroller.

Top 10 Projected Capacitive Highlights

• Wear resistant
• Works with water
• Exceptional optics
• High resolution abilities
• Touch coordinates are drift free
• Operates in environmental extremes
• Multi-touch capable - up to 10 fingers
• Works with finger, gloves and any pointing device
• Plastic versions are light-weight and break-resistant
• Flexible sensors can be contoured to curved surfaces

The resistive touch screen consists of a glass layer with a conductive coating on top and 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 resistive design (the most commonly used kind of resistive screen in large format POS applications), a voltage is applied to the 4 corners of the glass layer. When a person presses on the top sheet, its conductive side comes in contact with the conductive side of the glass, effectively closing a circuit (this is called pressure sensing). The voltage at the point of contact is read from a wire connected to the top sheet.

Top 5 Resistive Highlights

• Low cost solution
• Multi-touch capable
• Low power consumption
• Liquids do not affect touch screen performance
• Works with finger, gloves and any pointing device

Disadvantages

• Requires periodic recalibration
• Less durable than other touch technologies
• Lower transmittance and overall optical quality

Film / Film / Glass Resistive

Film / Glass Resistive

The surface capacitive touch screen 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.

Top 5 Surface Capacitive Highlights

• Long lasting
• High optical clarity
• Ideal for public access applications
• High impact, vandal, and scratch resistant
• Unaffected by moisture, rain or temperature

Disadvantages

• Requires periodic recalibration
• Only accepts finger input (or a special, tethered conductive stylus)
• Accuracy is dependent on capacitance of person touching the display
• Susceptible to electromagnetic interference which can cause an erratic cursor location