Optical heart rate monitoring based on X-NUCLEO-IKA01A1 expansion board

The X-NUCLEO-IKA01A1 is a multifunctional board based on ST operational amplifiers and it embeds several configurations. In this design tip we will use two of them to build an optical heart rate monitor (OHRM). We will also show how to connect Bluetooth BLE expansion board X-NUCLEO-IDB05A01 to the heart rate monitor and how to send data to your smart phone. This design tip will make easier to build a prototype of your own wearable optical heart rate monitor.

Optical heart rate monitoring is a simple method to determine one’s heart rate without using electrodes. It uses the optical characteristics of hemoglobin, which attenuates light based on the concentration of oxygen in the blood. Each time the heart beats, it brings fresh blood with oxygen to the muscles. The muscles use the oxygen and decrease its concentration. Therefore we are able to determine the heart rate from the time dependency of oxygen concentration in the blood.