Heart rate and blood oxygen saturation level are essential medical parameters that can be measured optically by photoplethysmography. However, certain individuals present variability in skin absorption that can affect the proper quantification of both pulse and blood oxygen level. In this work, we designed an optical device capable of measuring these variables, trying to improve the accuracy by means of different electronic signal processing. A final accuracy of 0.5 beats per minute and 0.5% was determined for the heart rate and the oxygen saturation measurements, respectively. The sensor was used in one practical study with more than 100 participants where the resting heart rate and the pulse waveform were analyzed. Resting heart rate was shown to decrease with age and increase with BMI. Overall, the device performance makes it suitable to be used in the medical field and sports science.

The United Nations marks responsible consumption and production as one of the 17 key goals to fulfill the 2030 Agenda for Sustainable Development. In this context, affordable precision instruments can play a significant role in the optimization of crops in developing countries where precision agriculture tools are barely available. In this work, a simple to use, cost-effective instrument for spectral analysis of plants and fruits based on open-source hardware and software has been developed. The instrument is a 7-band spectrophotometer equipped with a microprocessor that allows one to acquire the reflectance spectrum of samples and compute up to 9 vegetation indices. The accuracy in reflectance measurements is between 0.4% and 1.4% full scale, just above that of high-end spectrophotometers, while the precision at determining the normalized difference vegetation index (NDVI) is 0.61%, between 3 and 6 times better than more expensive commercial instruments. Some use cases of this instrument have been tested, and the prototype has proven to be able to precisely monitor minute spectral changes of different plants and fruits under different conditions, most of them before they were perceptible to the bare eye. This kind of information is essential in the decision-making process regarding harvesting, watering, or pest control, allowing precise control of crops. Given the low cost (less than USD 100) and open-source architecture of this instrument, it is an affordable tool to bring precision agriculture techniques to small farmers in developing countries.