Capacitive touch has become a ubiquitous form of user interface, encompassing touch screens, touch buttons, and even linear/circular sliders. Touch elements appear in everything from cell phones to appliances to information and Point-Of-Sale (POS) kiosks. However, even with their phenomenal success, capacitive touch solutions are still locked out of some applications due to physical limitations of their design.

This exclusion can be caused by capacitive touch’s sensitivity to water or the very field effect nature of the interface. For example, any application that involves Braille is excluded because users must be able to brush their fingers over the sensors to read the button legend. Interfaces that must operate near water or wet areas similarly exclude capacitive touch without complex filtering and decoding logic. Capacitive touch interfaces also have trouble with actuators other than fingers such as fingernails or gloved hands.

So far, these exclusions have typically relegated user interfaces to traditional mechanical buttons; however, with the introduction of Microchip’s new Metal Over Cap touch systems, these limitations are no longer valid. Metal Over Cap touch (Figure 1) uses a flexible metal plate suspended above the capacitive touch sensors to shield the capacitive touch sensor from the effects of water and noise and to translate the user’s press into a capacitive shift that can be detected and decoded with Microchip’s mTouch™ capacitive touch system.

This powerful combination allows operations in both wet and submerged applications. The translation of the user’s press into a physical motion removes the user from the electrical field of the sensor. This eliminates a common pathway for noise and opens the door for sensing a press by finger noise, styluses, and even gloved hands and booted feet.

The electrical and software interface to the Metal Over Cap touch system is the same high-resolution capacitive touch interface used by Microchip’s existing mTouch system. In fact, an existing mTouch™ design can be converted into a Metal Over Cap touch system with the addition of a metal cover. The secret is in the design of the flexible metal target. This target can take the form of a solid metal fascia layer with the user interface printed on its top side or a thin metal layer bonded to the back of a plastic fascia. The mechanical design of the metal target determines the required actuation force as well as the shape and placement of the buttons on the interface.

To help customers design Metal Over Cap touch systems, Microchip provides design information and access to design partners skilled in the mechanical design aspects of metal over capacitive sensing. In addition, demonstration boards and development systems are available to help evaluate technology, design new systems, and convert existing capacitive touch systems. Combined with Microchip’s wide variety of microcontrollers and no license fee open architecture, these design tools will help users create a product that will wow their customers.

We make it easy to please everyone from supervisors to end customers with an elegant and intuitive user interface, and a simple and cost-conscious design. For more information on Microchip’s Metal Over Cap technology, see the Touch interfaces Tech Channel product page. Microchip application teams are ready to help you design Metal Over Cap technology into your solution.

Microchip Technology is a leading provider of microcontroller, analog, and Flash-IP solutions. Products include 8-, 16-, and 32-bit PIC® microcontrollers, 16-bit dsPIC® digital signal controllers, analog and interface products, and serial EEPROM memory products. Microchip offers outstanding technical support along with dependable delivery and quality.

Keith Curtis is technical staff engineer with the Security, Microcontroller, and Technology Development Division at Microchip Technology Inc., where he develops training and reference materials for incorporating microcontrollers into a variety of designs. His experience includes engineering design and management roles at Summit Engineering, Tele-Tech, and Bally Gaming. Keith has a BS in Electrical Engineering from Montana State University.

Microchip Technology www.microchip.com