Touch screen is widely used in various areas of our daily life, such as mobile phones, media players, navigation systems, digital cameras, digital cameras, digital photo frame, PDA, gaming devices, monitors, electrical control, medical equipment, etc.
Universal touchscreen technology including applicable to mobile devices and consumer electronics products of resistive touch screen and projection capacitive (projected capacitive) touch screen as well as any other application of surface capacitive (surface capacitive) touchscreen, surface acoustic wave (SAW) touch screen and infrared touch screen.
Resistive touch screen
Application more resistive touch screen (Figure 1) has the air gap and the interval between two layers of ITO (Indium Tin Oxide, indium tin oxide).
Resistive touch screen is a high-volume applications, proven, low-cost technology. The drawback is: weak mechanical properties; stacking thick, relatively complex; you cannot detect multiple finger movements; front panel solution easily damaged; limited industrial design options; poor the optical performance; requires user calibration.Figure 1 resistive touch screen
Projected capacitive touch screen
Touch screen capacitance touch control using a conductive material (such as ITO) coating on the surface storage charge.
Conductive material along the x axis and Y axis conduction current. When transmission (such as a finger) touch control electric field changes, and can be identified along the horizontal axis and vertical axis the touch location. In the location with the key touch application, the separation of the sensor is placed in a specific location in the following key, when the electric field sensor is interference system records the touch and location. Projected capacitive touch screen shown in Figure 2.Figure 2 projected capacitive touch screen
Projected capacitive touch screen than other touch screen technology is:
Excellent signal to noise ratio; the entire touch screen surface with high precision; able to support multiple touch; through the "thick" dielectric materials for induction; no user calibration.QTouch technology
QTouch technology is Atmel touch technology department formerly known Quantum (quantity of research and technology) of the patent.
The development of integrated circuit technology is based on the charge-transfer capacitive sensing. QTouch IC detection using the sensor chip and simple press electrode connection to detect between single-touch (Figure 3). QTouch devices for sensing electrode capacitance of unknown charging to a known potential. Electrodes are usually printed circuit board of a piece of copper area. In one or more charge-transfer cycle measurement charge, you can determine the sensor plate capacitor. Press the fingers on the touch surface, resulting in the point of impact charge flow of external capacitor. Such as a touch records. You can also determine the QTouch microcontrollers to detect finger's proximity to absolute touch. Determine the logical signal processing of sound and reliable the QTouch. You can eliminate anti-static pulsed or transient unconsciousness touch or near fires caused by false.Figure 3 diagram of the Qtouch technology
QTouch sensor can drive single key or multiple key.
Using multiple keys, you can set for each key 1 separate sensitivity level. You can use different size and shape of the keys to meet the functional and aesthetic requirements.QTouch technology can be used in two modes: normal or "touch" mode and high-sensitivity or "near" mode.
Charge transport with high-sensitivity closer to the end user to detect sensor close to fingers, using the user interface interrupt electronic equipment or electrical device to start the system functionality.For superior electromagnetic compatibility, QTouch sensor using spread spectrum modulation and sparse, random charging pulse (with long delay between pulses).
Single pulse to pulse interval than internal strings short 5% or less. The advantage of this approach is a low cross sensor reduces RF interference, radiation and susceptibility, and low power consumption.Changes for slow QTouch devices (due to aging or environmental conditions change) with automatic drift compensation.
These devices have dozens of dynamic range, they do not require coil, oscillator, RF components, special cables, RC network or a large number of discrete components. QTouch as a project, it is simple, durable, compact package.In a few touch close proximity, can cause the fingers more key changes in capacitance.
Atmel patent o key inhibitors (AKS) uses iterative techniques for repeat measurements on each key, capacitance change comparison results and determine which keys is the users want. AKS suppression or ignore messages from all other key signal, the signal of the selected key. This prevents false on adjacent keys touch detection.Touch screen system design
A touch-screen system include: front panel, sensor-film, display unit, controller board and integration support (Figure 4).
Figure 4 touch screen system
Atmel Corporation provides touch controller IC, control circuit board reference design, the sensor reference design, integration, support and sensor test device design, and partner with sensor thin, sensors and a front panel integration and controller board.
Atmel provides for 1 to 10 press and/or slider/pulley of devices-QTouch series; used for up to 48 press and/or slider/pulley of devices-QMatrix series; for Single Touch and Two Touc
H touch screen devices QFild and QTwo series. Which adopts QT5320/5480 devices easy system shown in Figure 5, touch screen, slider, pulleys and/or key can be used by the host via I2C-compatible interface.Figure 5 a simple system of touch screen
Reference documents:
[1] von 子龙, Atmel's capacitive touch screen system solutions, September 2008 Beijing presentation
[2] www.appliance DESIGN.com
[3] www.atmel.com/touchscreen
[4] AT42QT5320 detasheet,Atmel
[5] AT42QT5480 datasheet,Atmel
[6] Zheng praise, touchscreen multi-touch technology secret, electronics world, 2008.11
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