The IR Topled D5140 fitness monitor sensor is the updated version of the SFH 2440 photodiode from Osram Opto.
Heart rate measuring occurs when the light hitting the skin’s surface is absorbed by the detector. The blood in the arteries absorbs more light than the tissue surrounding it, the detector signal strength changes according to the volume of blood where the light passes.

(Credit: Osram Opto)
Key features:
- Measures 5.1 mm, requiring less PCB space
- Sensitivity of 620 nanometers
- Signal-to-nose ratio while suppressing infrared light
- Short switching time, allowing light signal controlled with heart rate to be time-resolved
For more informatin, visit: www.osram.com.