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New capacitive touch sensor interface

Posted: 29 Jun 2005 ?? ?Print Version ?Bookmark and Share

Keywords:sensor? capacitive touch? psoc? mixed-signal? switches?

Cypress Semiconductor Corp. introduced CapSense technology, a new capacitive touch sensor interface based on its Programmable System-on-Chip (PSoC) mixed-signal arrays. A single PSoC device can replace dozens of mechanical switches and controls with simple, touch-sensitive controls. CapSense-based "button" and slider controls are more reliable than their mechanical counterparts because they are not prone to the environmental wear-and-tear that affects exposed buttons and switches.

The CapSense solution offers system designers numerous advantages over capacitive touch sensor products built around modules and sub-assemblies, including increased flexibility, reduced board space and lower cost. Because of the unique PSoC architecture, designers can easily integrate multiple functions (e.g., LED drivers and LCD displays), in addition to touch sensing. The PSoC CapSense solution also delivers benefits such as easy serial communications using either I2C or SPI interfaces, the ability to implement both trackpad (x-y matrix) and linear slider applications with the same device, and the ability to make quick design changes using the flash-based PSoC architecture.

capacitive sensing is fast becoming the solution of choice for front-panel display and media control applications. Increased durability, decreased bill-of-materials (BOM) and a clean, minimalist appearance make this elegant interface attractive to a wide range of designs. With CapSense technology, a finger on the interface forms an electrical connection with embedded sensors, which work with the PSoC device to translate data about the finger's position into various system control functions. Cell phone users can slide a finger along their screen to change the volume of a call, the brightness of the screen or the loudness of a ring tone without having to end the call and click through complicated menu structures. In notebook computers, 'touchpad' sensors have already replaced external mice for cursor movement. Applications abound in consumer, industrial, white goods, automotive and medical devices-in short, any area where durability, ease of use and price are major considerations.

"CapSense is a smaller, cleaner, more flexible solution to implement control functions in any sort of electronic device," said Rich Kapusta, PSoC marketing director for Cypress. "In portable consumer devices - particularly cell phones, PDAs, and notebook computers - CapSense provides an attractive interface and product differentiation that adds real value to the system. At the same time, CapSense designs are cheaper and easier to manufacture than ones using thumb switches and potentiometers. Both the manufacturer and consumer come out ahead."

CapSense is built around Cypress's CY8C21x34 family of PSoC devices. Cypress's PSoC mixed-signal arrays are programmable SOCs that integrate a microcontroller and the analog and digital components that typically surround it in an embedded system. A single PSoC device can integrate as many as 100 peripheral functions and a microcontroller, saving customers design time, board space, power consumption, and system costs. Future PSoC offerings will also support CapSense.

In addition to PSoC, Cypress provides designers with CapSense application notes (AN2233a and AN2277); source code; example designs; a Front-Panel Display Demonstration Kit (CY3220-FPD); a Slider Demonstration Kit (CY3220-Slider); design software and support.


The CY8C21x34 comes with 8Kb of flash for program storage; 512 bytes of SRAM for data storage; a maximum speed of 24MHz; and is available in 16-pin SOIC, 32-pin MLF and 20 and 28-pin SSOP packages. The product is available now for $0.99 in production quantities. The Front Panel Display Demonstration Kit (CY3220-FPD) is available for $75 through the Cypress online store at The CapSense application notes (AN2233a and AN2277) are available at no charge in the "Design Resources >> Application Notes" section at the company's website.

High-resolution photos of both CapSense and the Front Panel Display Demonstration Kit (CY3220-FPD) are available at

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