What is the difference between projected capacitive touch and capacitive touch?

In the world of interactive displays, "capacitive touch" is a ubiquitous term, most famously associated with the sleek screens of our smartphones and tablets. However, not all capacitive technologies are the same. The key distinction lies between the older Surface Capacitive Touch and the modern, more advanced Projected Capacitive Touch (PCAP). Understanding this difference is crucial for designers, engineers, and consumers alike.

To be precise, when people say "capacitive touch," they are often referring to the older Surface Capacitive technology. When they talk about modern smartphones, they are referring to Projected Capacitive. Therefore, the real comparison is between these two specific implementations of capacitive sensing.

Part 1: The Fundamental Principle They Share

Both technologies operate on the same fundamental principle: they detect changes in capacitance.

• Capacitance is the ability of a system to store an electrical charge.

• The Human Body as a Conductor: The human body is a good electrical conductor. When you touch a capacitive screen with your finger (which is conductive), it disturbs the screen's electrostatic field, causing a measurable change in capacitance at the point of contact.

• No Physical Pressure Needed: Since they detect conductivity, neither technology requires physical pressure to register a touch. A light, gentle contact is sufficient.

Where the two technologies diverge significantly is in their implementation, structure, and capabilities.

Part 2: Surface Capacitive Touch

Surface Capacitive was the first commercially successful capacitive technology, often used in public kiosks, ATMs, and industrial controls before the smartphone revolution.

How It Works:

1. Structure: A single layer of a transparent conductive film (typically Indium Tin Oxide or ITO) is coated on a glass substrate. This layer forms a uniform electrostatic field across its surface.

2. Electrodes: Electrodes are positioned at the four corners of the glass substrate.

3. Sensing: When a finger touches the screen, it draws a tiny amount of current from the electrostatic field. The sensors at the four corners measure the ratio of this current flow to determine the X and Y coordinates of the touch point.

Key Characteristics of Surface Capacitive:

• Single-Touch Only: It can only accurately detect one touch point at a time.

• Durability: The hard glass surface is highly durable, scratch-resistant, and can be sealed to meet IP ratings for dust and water resistance, making it suitable for harsh environments.

• Input Method: Works with a bare finger or a special capacitive stylus. It does not work with a gloved hand (unless the glove has conductive fingertips) or a standard passive stylus.

• Optical Clarity: Good, but the single ITO layer can cause some light reflection.

• Cost: Generally less expensive to manufacture than PCAP for larger sizes, though this is changing.

Limitations:

• Lack of Multi-Touch: Its inability to support gestures like pinch-to-zoom is its primary drawback in the modern era.

• Accuracy: Can be less accurate than PCAP, especially near the edges of the screen.

• Susceptibility to Environmental Factors: Can be affected by moisture, dirt, and electromagnetic interference.

Part 3: Projected Capacitive Touch (PCT/PCAP)

Projected Capacitive is the technology that powers virtually every modern smartphone, tablet, and high-end touch device. It is a massive evolutionary leap over Surface Capacitive.

How It Works:

1. Structure: Instead of a single conductive layer, PCAP features a grid of transparent, microscopic electrodes (made of ITO or newer materials like silver nanowire or metal mesh). This grid is typically embedded between two layers of glass.

2. The Matrix: The electrodes are arranged in rows on one layer and columns on another, forming a precise matrix of capacitors (or "nodes") across the screen.

3. Sensing: The controller chip continuously scans this matrix. When a finger comes into proximity (it doesn't even need to make full contact), it projects an electrical field onto the grid and alters the capacitance at the specific nodes (intersections of rows and columns) near the touch point. The controller can pinpoint the exact location with high precision by identifying which nodes were affected.

Key Characteristics of Projected Capacitive:

• True Multi-Touch: Its matrix structure allows it to independently track multiple touch points simultaneously. This enables complex gestures like pinch, zoom, rotate, and multi-finger gaming.

• High Accuracy and Resolution: The dense grid allows for extremely precise touch detection.

• Proximity Sensing: It can detect a finger before it physically touches the screen, enabling features like "tap-to-wake."

• Durability: The sensor grid is protected between layers of glass, making it very robust and resistant to surface scratches. It also offers excellent optical clarity.

• Input Method: Works with a bare finger, but also supports fine-tipped active styli for precise input. It generally does not work with a gloved hand, though "thick glove" modes exist that increase sensitivity.

Limitations:

• Cost: Historically more expensive, though economies of scale have made it very affordable for consumer devices.

• Complexity: Requires a more sophisticated controller and design.

• Sensitivity to EMI: Can be interfered with by strong electromagnetic noise.

Part 4: Summary Table of Differences

Feature	Surface Capacitive	Projected Capacitive (PCAP)
Basic Principle	Measures current leak from a single conductive layer at the corners.	Scans a matrix of capacitors (nodes) formed by rows and columns of electrodes.
Touch Points	Single-touch only.	True multi-touch (e.g., 5, 10, or more simultaneous touches).
Durability	High (hard glass surface).	Very High (sensor is sandwiched between glass layers).
Accuracy	Good, but lower near edges.	Very High.
Input Method	Bare finger, capacitive stylus.	Bare finger, active stylus.
Optical Clarity	Good.	Excellent.
Cost (for large sizes)	Traditionally lower.	Traditionally higher, but decreasing.
Common Applications	ATMs, Industrial Kiosks, Public Terminals.	Smartphones, Tablets, Laptops, High-end Monitors, Automotive Displays.

Conclusion

While both Surface Capacitive and Projected Capacitive are "capacitive" technologies, Projected Capacitive is a clear and superior successor. Its ability to enable precise, multi-touch interaction is the foundational technology that made the modern touch-centric computing era possible. Surface Capacitive still has its place in cost-sensitive, single-touch applications where extreme durability is needed, but for any device requiring intuitive, gesture-based interaction, Projected Capacitive is the undisputed and ubiquitous standard.