Hugo Silva, secretary of IEEE EMBS Portugal Chapter, presented this online class about Biosignals to U. Coimbra. Low-cost computing platforms, such as the Arduino and Raspberry Pi had a transformational role in the way people learn, experiment, and create imaginative solutions to outstanding problems that can benefit from embedded systems. Within biomedical engineering, physiological sensing is increasingly capacitated with analogous albeit specialised resources, the added value of which is being recognised by policymakers and practitioners across different disciplines. As a result, low-cost and open source tools for physiological sensing are providing new opportunities for biomedical engineers at different states of their careers, ranging from their first years of study to research and/or professional practice. During this talk you will learn how to benefit from low-cost hardware and open source software to boost learning, research, and rapid prototyping in the field of biomedical engineering. We will review the basic concepts, show multiple projects and applications involving physiological sensing, explore modular wireless biosignal acquisition systems for real time data acquisition, and become familiar with useful software resources.