Not all touchscreens are created equal. There are many different touch technologies in use today, each with their own strengths and weaknesses. For example, resistive touch technology is relatively simple and widely available. A touch is sensed when a pressing force bends a conductive layer into contact with another below it, creating a voltage divider-type circuit. Resistive touchscreens can enable higher resolution at a lower cost when compared with capacitive touchscreens.
In comparison, capacitive touchscreens can offer superior optical qualities. Also, a flexible top layer is not required, so capacitive screens can be made highly durable and environmentally resistant. Surface capacitive touchscreens, an earlier technology still in use, contain a single conductive sheet coated with an electrically insulative layer. Projected capacitive touch sensors are a more recent development, ideal for small to medium sized screens and widely used in smartphones.
Many other touchscreen technologies exist such as surface acoustic wave (SAW) and various optically based devices. Though generally higher in cost, these sensors are unobstructive, offering the highest optical performance. Infrared and camera based touch sensors are especially attractive options for designing very large (>50") screens, something that is difficult to achieve with other technologies.
A touch overlay, or panel, is essentially the sensor portion of a touch display, but in discrete form. Together with a controller, touch overlays can enable touch sensing for designs using LCD displays that lack this function.
There are many different touch technologies in use today, each with their own strengths and weaknesses. For example, resistive touch technology is relatively simple and widely available. A touch is sensed when a pressing force bends a conductive layer into contact with another below it, creating a voltage divider-type circuit. Resistive touchscreens can enable higher resolution at a lower cost when compared with capacitive touchscreens.
Touch controllers interact with a touch sensor to measure tiny changes in capacitance or resistance, which are then translated into digital signals. Most controllers are designed to interface with a host processor to indicate finger/stylus positions (in the case of touchscreen controllers), taps, and other useful input. There are many reasons for using a dedicated touchscreen controller instead of the common A/D converters found in a microcontroller. For example, implementing capacitive sensing with a generalized MCU can drastically increase the amount of "on-state" time and may require more A/D inputs than are available. Touch controllers and specialized touch sensing MCUs can provide superior accuracy, noise handling, algorithm efficacy, and environmental compensation techniques.
Mouser offers the newest touch controllers for a wide variety of touch sensing applications such as 4- and 5-wire resistive touchscreens, capacitive sliders and buttons, and even controllers for the latest surface- and projected-capacitive touchscreens. Also available are capacitive proximity sensor controllers, many of which include auto-tuning or continuous self-calibration features to make implementation that much easier, as with the Azoteq IQS259 and Freescale’s MPR121.
Touch sensing represents a spectrum of rapidly evolving technologies. As design complexity increases and design cycles continue to shrink, development tools are often all but essential. In the area of touch sensing, development kits and boards provide designers the means to evaluate and become familiar with the latest touch technologies and products.
The often iterative process of design must include development and testing beyond mere circuit simulation. Engineers frequently find themselves resorting to the seemingly inevitable Breadboard. Development kits offer a rapid method of getting to the heart of development with little set-up time.
In addition to accelerated time-to market, development kits can further provide the benefits of directly applicable, pre-tested circuits, readily available printed circuit board (PCB) layouts, and a common platform from which to create and debug customized designs.
From simple button and slider evaluation boards to large, comprehensive development kits featuring liquid crystal displays with integrated capacitive touchscreens, Mouser offers the newest tools for a broad range of touch sensing applications.