Digital ultraviolet index sensors will add a function to wellness monitoring

February 11, 2014 // By Graham Prophet
Silicon Labs’ single-chip Si1132/4x optical sensors track UV exposure, ambient light and other biometrics to add health-monitoring functions to smartphones and wearable computing products. They also provide display-backlight compensation for all lighting conditions.

The single-chip digital ultraviolet index sensor ICs measure UV sun exposure, heart/pulse rate and blood oximetry and provide proximity/gesture control. In Silicon Labs’ optical sensor family, the Si1132 and Si114x sensor ICs are designed for activity-tracking wrist and arm bands, smart watches and smartphone handsets. In addition to enabling UV index sensing, the devices also provide ambient light and infrared (IR) proximity sensing capabilities for health and fitness applications.

Developers, Silicon Labs says, seek to differentiate wearable and handset products with new features that help protect people from harmful UV light exposure. UV sensor-equipped products can measure cumulative UV exposure and alert end users before they have reached unhealthy exposure levels while exercising outdoors. Standardised by the World Health Organization (WHO), the digital UV index is linearly related to the intensity of sunlight and is weighted according to the Erythemal Action Spectrum developed by the International Commission on Illumination (CIE). This weighting provides a standardized measure of our skin’s response to different sunlight wavelengths including UVB and UVA.

Conventional UV sensors combine UV-sensitive photodiodes with an external microcontroller, analogue-to-digital converter and signal processing firmware. Silicon Labs has combined this functionality into a single-chip in a 2 x 2 mm package. The variants comprise;

• Si1132 UV index and ambient light sensor with an industry-standard I2C interface to read digital UV index values.

• 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 Si1132 and Si114x sensors enable developers to implement sleep tracking in wearable applications. In addition, the sensors’ ability to measure both infrared and visible light levels enhances the control of LCD backlighting in mixed-light source environments. The result is an inexpensive yet effective means of adjusting backlighting to ease eyestrain and reduce power without distracting the end user.

The Si114x sensors’ LED drivers enable implementation