In his blog, Charalampos describes his experience with SeeedStudio’s Grove Ear-clip Heart Rate sensor and Cosm (former Pachube) cloud service.
The employed sensor is quite cheap and can detect heart pulses from the ear lobe, by measuring the infra-red light reflected by the tissue and by checking for intensity variations.
By connecting this sensor with an ADK board and, in turn, with an Android smartphone, Charalampos implemented a portable heart-rate tracker, which is used to send the recorded data to Cosm cloud service.
For more detail: Portable and cloud-based heart rate tracker
