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Human-interface-design package mixes capacitive and IR sensing

Silicon Labs offers multi-mode package with a single design tool set

Silicon Labs has combined sensing of touch (using capacitive techniques) proximity (using infrared) and ambient light to product a package of human-interface products under the name QuickSense. The company based its C8051F800 touch-sensing microcontroller on its low-power, single-cycle, 8051 core. The F800 MCU uses a capacitance-to-digital converter (CDC) with a 40 μsec acquisition time, combined with the 25 MIPS CPU, to provide button, slider and wheel functions. Tolerance of production variations and changes in ambient conditions is assisted by the device’s internal 16-bit resolution. The CDC uses only part of the MCU’s time, allowing it to host simple applications without requiring any other processors. A 10-bit ADC that operates independently of the CDC is part of that offering, as is a range of peripherals, and multiple digital I/Os. In such an application, the CDC can be the only part of the device not powered-down, offering a wake-on-touch facility for low-power operation. SiLabs says that the sensor uses hardware averaging and is insensitive to low-frequency noise and dc offsets. Early in 2010, SiLabs will add to the F700 series of MCUs for use with capacitive touch screens, supporting two-finger touch and, later, multi-touch.

SiLabs has also acquired the technology for a low-power infrared sensing system, in the form of the Si1102 proximity sensor and the Si1120 proximity and ambient light sensor. You might use them for tamper-detection – alarm-on-enclosure-opening, for example – or for gesture interpretation. The QuickSense Si1102 gauges its proximity to the user, over a range out to 50 cm. For example, it can detect if a handset is near a user’s face and adjusts the display and lighting accordingly. The QuickSense Si1120 infrared proximity and ambient light sensor can also detect the light in the external environment, allowing dimming screen backlighting. Rather than relying on ambient light sources, you can illuminate an area with pulsed drive to two IR-emitting LEDs; software running on an MCU can interpret IR sensor measurements to resolve proximity and direction of movement, allowing gesture inference. A pre-defined feature allows you to implement a completely touchless, “mid-air” slider control. When you use an illuminating LED it typically runs at 100 mA, pulsed for only a few milliseconds, making the detector insensitive to any ambient fluorescent-light flicker. The sensing part of the offering uses under 1 mA, SiLabs says. The single-pulse proximity measurement technique, as opposed to a multiple-pulse-integration method, can improve power efficiency by a factor of up to 4000x, according to its designers. It is fully compatible with industry-standard components such as IR LEDs and lenses.
You configure all of the new devices in QuickSense Studio, a common development environment. A configuration wizard allows designers, using a software GUI, to select functions such as capacitive touch sense buttons, sliders and wheels, and then easily auto-generate the software to set up and calibrate these functions. Designers can also test their implementation and review a graphical display of the system performance. The microcontrollers are priced in the $1-2 range, with the sensors costing somewhat less per unit; a development kit, C8051F800DK, costs $99.99, including QuickSense Studio, IDE, and target board.
Silicon Laboratories, www.silabs.com/quicksense