Heart rate measurement in LabVIEW

This is one of my project in which I have designed a transducer that can measure the variations in oxygenated hemoglobin and deoxygenated hemoglobin ( simply known as an oximeter).The sensor was developed based on the key principle that these two parameters have two different optical spectra in the range of 500nm to 1000nm. Hence, two light sources of two different wavelength(red-660nm and infra red-940nm) are used. A photo diode was used to sense absorption rate and the output of the photo diode was obtained in the LabVIEW using a data aquisition card(NI 6211).  The photo plethysmograph(PPG) waveform was obtained in LabVIEW by driving the leds using PWM signals of 25% duty cycle. Hence, based on the PPG waveform, the heart rate(Beats Per Mintue) was found.

This is the video of the PPG waveform obtained in the LabVIEW. Since ordinary sensors was used, there were lot of noise interference in the reading and the BPM was very fluctuating.

(the PPG waveform in the video is a recorded measurement file of the actual experiment)

This is the PWM pulse which was generated to drive the LEDs from the LabIEW. LEDs are switched alternatively at same duty cycle.

Shown below is the transducing part which I have developed in my college laboratory,

“Simulation” is always a good idea before an actual execution of a project. I have simulated the transducing circuit in NI Multisim and it helped me a lot in actual implementation. Following is the video of the simulation. 

I have used the current source since the output of a photo diode is current and used an I-V converter to convert it into voltage( since input of NI 6211 must be in volts). Here I have also added a sample and hold circuit to hold one led`s value while other is being sampled and vice versa. The manual switch in the simulation was replaced with the control signal from the LabVIEW.

Though the acquired results got some flaws, obtaining a biological parameter was really awesome!