Digital ultraviolet index sensor tracks light for wearable computing

Claimed to be the industry’s first single-chip digital ultraviolet (UV) index sensor ICs to track UV sun exposure, heart/pulse rate and blood oximetry and provide proximity/gesture control, the Si1132 and Si114x sensor ICs have been added to Silicon Labs’ portfolio.

They can be used for activity-tracking wrist and arm bands, smart watches and smartphone handsets. In addition to UV index sensing, the devices also provide ambient light and infrared (IR) proximity sensing capabilities for health and fitness applications.

UV tracking is helpful for those with elevated risks of sunburn or concerns about excessive sun exposure. UV sensor-equipped devices can measure cumulative UV exposure and alert users before unhealthy exposure levels are reached.
Conventional UV sensors combine UV-sensitive photodiodes with an external microcontroller, ADC and signal processing firmware. Now, this is available in a single-chip that measures just 2x2mm.

The UV sensor family includes the Si1132 UV index and ambient light sensor with an industry-standard I²C interface to read digital UV index values and the Si1145/46/47 UV and IR proximity/ambient light sensors, offering a choice of one, two or three integrated LED drivers with 15 selectable drive levels for gesture detection.

When combined with an accelerometer, the sensors enable developers to implement sleep tracking in wearable applications. The sensors measure both IR and visible light levels enhances the control of LCD backlighting in mixed-light source environments to adjust backlighting to ease eyestrain and reduce power without distracting the user.

The sensors’ LED drivers enable implementation of reflective heart rate and blood oximetry measurement capabilities for health and fitness trackers, as well as touchless interfaces. Offering two and three IR LED drivers respectively, the Si1146 and Si1147 sensors enable advanced motion and gesture sensing. The Si1146 enables motion sensing and touchless control in the z- and x-axis, and the Si1147 adds a third axis. Both provide reflectance measurements that can be post-processed to determine gestures.

The low-power architecture enables thinner wearable designs with smaller batteries and extends battery life with as little as 1.2 µA average current for once-per- second UV measurements. The IR sensor is claimed to provide longer battery life in motion sensing/gesture applications through the use of a single 25.6 µs IR-LED on-time while enabling up to 500mm sensing range. Dynamic adjustment of LED currents further minimizes power consumption.

Hardware and software tools are available to simplify testing, characterisation, prototyping and software development, including the UVIrSlider2EK UV/IR evaluation kit.

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