LED-based sensors for wearable fitness tracking products

December 19, 2014 // By Joerg Heerlein and Tilman Ruegheimer
LED-based sensors for wearable fitness tracking products
Joerg Heerlein and Tilman Ruegheimer consider LED-based sensors for wearable fitness tracking products.

More and more people are tracking their physical fitness with the aid of wearable gadgets and appropriate apps. Optical sensors are suitable for measuring pulse rates and oxygen saturation in blood. The technology has long been established in the medical sector and can now be transferred to consumer applications thanks to modern LED technologies.

Fig. 1: The "Quantified Self" movement -- in short, self-knowledge through self-tracking with technology -- is growing. Millions of people are using fitness trackers, and the numbers are increasing. With the aid of optical sensors, trendy armbands and smartwatches can measure pulse rate and oxygen saturation in the blood.

It all started with armbands that could record the number of paces a person took. Now, many activity trackers such as fitness armbands and smartwatches can also measure heart rate and other biometric values or monitor sleep quality. The new opportunities for tracking your own fitness levels have been enthusiastically embraced by many people, leading to a growing "Quantified Self" movement. Major players such as Samsung, Apple and Google are now entering this growing market with appropriate apps, smartwatches and smartphones.

Whereas pace counters use acceleration sensors, optical methods traditionally used in the medical sector for pulse and blood oxygen measurements are now finding their way into the consumer market. In the hospital environment, the sensors are mostly installed in ear or finger clips. In 2013, the Mio Alpha smartwatch was the first armband that could measure the pulse rate at the wrist using an optical sensor – a significant advance compared with the chest belt worn by athletes, which no one would enjoy wearing all day. Smartphones are also able to measure pulse rates on a finger. The first fitness armbands are now coming onto the market that enable you to measure the oxygen saturation in your blood simply by placing your finger on a screen. This feature is useful, for example, for people engaged in activities at high altitudes, such as mountain climbers, hang-gliders and glider pilots, and also for people with heart or lung problems.

Next: Optical measurement

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