Doing one device for measuring spO2 in blood
https://www.instructables.com/id/Simple-DIY-Pulse-Sensor/
https://altlab.org/d/m/jpralves/newsletters/2020/261/#Projetos-Maker
https://www.instructables.com/id/Arduino-Pulse-Oximeter/
https://hackaday.com/2010/05/02/diy-pulse-oximeter/
https://hackaday.io/project/170752-oximeter-do-it-yourself
https://create.arduino.cc/projecthub/SurtrTech/measure-heart-rate-and-spo2-with-max30102-c2b4d8
https://www.nxp.com/docs/en/application-note/AN4327.pdf
https://en.wikipedia.org/wiki/Pulse_oximetry