BH1790GLC Optical Heart Rate Sensor ROHM Semiconductor BH1790GLC Optical Heart Rate Sensor is a photodiode designed to measure pulse waves, which are changes in the volume of a blood vessel that occur when the heart pumps blood. Pulse waves are detected by measuring the change in volume using an optical sensor and a green LED. The BH1790GLC Optical Sensor features an optical filter optimized for pulse wave detection that minimizes the effects of ambient light and increases the sensitivity and accuracy of the sensor block.