Portable products such as iPods, MP3 players and universal remote controls use capacitive touch switch technology to easily navigate large menus. A resistive scroll ring interface provides a similar feel to the capacitive approach at a lower cost. White Electronic Designs’ SimScroll interface uses a patented conductive ink technology, called SimTouch, for a force-sensing resistor.
A flexible overlay laminated to the force-sensing resistor allows a low actuation force of 1.5 to 2.5 oz (43 to 71 gm). This low value and a very short travel distance simulate the experience of a capacitive touch switch. The use of different 0.010-inch (0.25-mm) polycarbonate overlay materials can provide a textured finish, smooth glass-like finish or brushed metallic for a stainless steel look.
Conductive circuitry below the force-sensing resistor material mounts to a polyester flex circuit with pressure-sensitive mounting adhesive to complete the layered structure. Nominal thickness of the entire structure is only 0.020 inch (0.508 mm). A force applied to the top of the structure changes the resistance from more than 1MOwhen open to less than 1KO when closed, causing electronics’ circuitry to perform the required switching. Activation pads can be screened directly on the overlay or on an additional polyester layer.
The sealed interface keeps out moisture, dust and dirt and is not affected by temperature or pressure changes. As a result, medical and industrial applications can take advantage of the one-piece sealed membrane switch. The resistive scroll ring and switch arrays can be integrated with flexible segmented displays to create touch panel functionality.