Touch Screen Knowledge and FAQ
There are many types of touch panel technologies available in the
market, the popular types are resistive touch panel (RTP),
surface capacitive touch panel, projected capacitive touch panel (PCAP
or CTP), surface acoustic wave (SAW) touch panel, Infrared (IR) touch
panel. The reason each type of touchscreen responds so differently is the
underlying technology. In this article, we are going to discuss the two
most widely used types, and compare resistive vs capacitive touch screen.
Capacitive Touch Panel
Projected Capacitive Touch Panel (PCAP) was actually invented 10 years earlier than the first resistive touchscreen. But it was no popular until Apple first used it in iPhone in 2007. After that, PCAP dominates the touch market, such as mobile phones, IT, automotive, home appliances, industrial, IoT, military, aviation, ATMs, kiosks, Android cell phones etc.
Projected capacitive touchscreen contains X and Y electrodes with insulation layer between them. The transparent electrodes are normally made into diamond pattern with ITO and with metal bridge.
Fig. 1. P-CAP X and Y electrode structure
Fig. 2. Metal Bridge in P-CAP
Human body is conductive because it contains water. Projected
capacitive technology makes use of conductivity of human body. When a bare
finger touches the sensor with the pattern of X and Y electrodes, a capacitance
coupling happens between the human finger and the electrodes which makes change
of the electrostatic capacitance between the X and Y electrodes. The
touchscreen controller detects the electrostatic field change and the location.
Fig. 3. Projected Capacitive Touch Sensor
Capacitive Touchscreen Advantages
In There are many advantages for P-CAP:
- Projected
capacitive supports multiple touches (Multi-touch), so it supports a lot
of gestures: Zoom in and out (pinch/spread), scroll, swipe, drag, slide,
hold/press, rotate, tap etc.
- Excellent
image clarity because of high transmission.
- Excellent
sensitivity.
- More
resistance to the scratches because the surface can be made by tampered
glass, such as gorilla glass or dragontrail glass which can have the
surface hardness of 9H. Only diamond can make a scratch.
- Resistance
to contaminants and liquid. It is easier to get clean of dust, grease,
moisture etc.
- With the
new development, projected capacitive touch panels can support gloved hand
touch with different glove materials and touch with water or even with
salt water.
Resistive Panel
Introduction
Before 2007, resistive technology was the most popular touch panel
market. From its name, we know that the technology relies on resistance.
A resistive touch screen is made of a glass substrate as the bottom layer and a
film substrate (normally, clear poly-carbonate or PET) as the top layer, each
coated with a transparent conductive layer (ITO: Indium Tin Oxide), separated
by spacer dots to make a small air gap. The two conducting layers of material
(ITO) face each other. When a user touches the part of the screen with finger
or a stylus, the conductive ITO thin layers contacted. It changes the
resistance. The RTP controller detects the change and calculate the touch
position. The point of contact is detected by this change in voltage.
Fig. 4. Resistive Touchscreen Technology (RTP)
Resistive Touchscreens Advantages
With the fast development of projected capacitive, resistive
touchscreen devices market is shrinking rapidly but it is still widely used in some
industrial applications because of the following advantages.
- Low cost
and simple manufacturing process.
- Low power
consumption and easy drive.
- Easily be
activated with any touch material as long as the pressure is applied
(finger, stylus, glove, pen etc.) (not keys to cause scratches on
surface).
- Robust during harsh climate and rugged environment and no false touch.
Resistive vs Capacitive Touch Panel
The following table shows the comparison of resistive and capacitive touch screens. It is up to your application to select the types of technology to use. VIEWE can provide both touch panel and Touch Enhancement Solutions : Glove Touch, Waterproof Touch , High Reliability and High Interference Resistance Touch
|
Resistive Touch |
Capacitive Touch |
|
|
Cost |
Low |
Relatively high, can
be low for especial design |
|
Multi-touch |
No |
Yes |
|
Touch Gestures |
Difficult |
Yes |
|
Touch Durability |
3H, easy scratch |
Can be as high as 9H,
hard to scratch |
|
Power Consumption |
Lower |
Higher |
|
Touch Sensitivity |
Low |
High (Adjustable) |
|
Touch Resolution |
High |
Relatively low |
|
Image Clarity |
Poor |
Good |
|
Touch Material |
Any type |
Fingers. Can be designed to use other materials like glove, stylus, pencil etc. |
|
Touch with water, oil |
No design change |
Need special design |
|
Surface Decoration |
Difficult |
Easy |
|
Different Shape |
Difficult |
Easy |
|
Overlay |
Can be done |
No |
|
3D surface |
Difficult |
Achievable |
|
Size |
Small to medium size |
Small to very big size |
|
Under Rugged
Environment |
Easy |
Difficult |
|
False Touch |
No |
Need careful
calibration |
|
functionality
Sensitive to EMI/RFI |
Low |
High, shield has to be
designed |
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