A heart rate sensor measures periods of time between each heartbeat. It uses the indicator of color change to do this. Blood travels through the body in one direction (away from the heart) full of oxygen and then travels back (without oxygen) to collect more, cycling through the body in this way. The oxygenated (arterial) and deoxygenated (venous) blood cells have slightly different optical properties (they react differently to light, which heart rate sensors can detect). With every heartbeat, there is a spike in oxygenated blood being pushed through the body. This makes a change in how much red/infrared light the sensor can detect, and how much is scattered through its blood.
In this module you will build a heart rate sensor and learn about how biofeedback systems moderate heart rate using negative feedback. You will learn about how a dance called La Bomba incorporates positive and negative feedback directly into the performance of the dance according to the drum rate.