FROM EDN EUROPE: Programmable array develops magic touch

Cypress Semiconductor has produced an optimised application for its PSoC configurable silicon product that carries out the sensing function in capacitive, touch-sensitive switches. PSoC is a programmable part that includes a small microcontroller core, non-volatile memory, SRAM and an array of programmable logic and programmable analogue and mixed-signal functions. The CapSense product integrates all of the circuitry that is needed to provide capacitive-based touch-activated switching, yielding a large saving on parts-count over other implementations. For each circuit the chip senses, the proximity of a finger alters the capacitance between two plates, which are themselves behind a non-conductive panel. There is no electrical contact between the activating touch and the circuitry—in fact, the isolation barrier can be of substantial plastic or glass. The capacitor is part of the frequency-setting loop of a relaxation oscillator. On-chip circuitry gates and counts the oscillator's output and uses the altered count as the detected signal. Designers can use CapSense to detect simple switch (on/off) actions, or finger-activated "slider" setting of a variable level according to where a fingertip touches or slides along a scale. A single IC can sense as many as 48 switch lines, and can host integral LED/LCD drivers, signalling output data via I²C or SPI interfaces (Picture). The 8-bit microcontroller in the PSoC, and the SRAM on-board, have sufficient free capacity to also host simple control applications, further reducing the bill-of-materials in applications such as complex front-panel design. In quantity, the chip will sell for under $1.00; demonstration kits illustrate front-panel design and slider configurations, and the company supplies complete source code.

Cypress Semiconductor, +44 1279 873160, www.cypress.com.