Heart Rate Monitor Using a myRIO

For NI week, we wanted to include a demo that used LabVIEW, the NI myRIO, the Analog Parts Kit, the myProto board, the PmodCLS LCD display, and the Pmod Adapter for the myRIO.  The idea I came up with was to use a photoresistor to measure your heart rate from your finger.  As your heart pumps, the blood volume in your finger changes depending on the stage of the heartbeat and thus the amount of light absorbed by your finger changes as well.  These different light values can then be used to see how many heart beats have occurred in a period of time.  Check out my Instructable for this project here.


Circuit Design:

First, a voltage divider is created using 5V supply from the myRIO, a 14.7k resistor, and the photoresistor.  The voltage across the photoresistor is then fed to a buffer op-amp to protect the voltage reading across the photoresistor from the load of the rest of the circuit.  The resulting voltage is then sent to a passive bandpass filter with both the low and high frequency cutoffs set to 2Hz using resistors and capacitors.  The filtered voltage is then amplified 101 times by using a non-inverting amplifier with a 1M resistor and a 10k resistor.  Finally, the amplified voltage is sent to the analog input on the myRIO.  The Op-Amp I used (ADTL084) acts like two Op-Amps packaged together.





When Button0 is pushed on the bottom of the myRIO, the LED1 on the myRIO turns on and the voltage is monitored for 10 seconds. The number of heart beats sensed during that time period is multiplied by 6 to give you a beats per minute reading which is then sent to the PmodCLS via SPI.  When the myRIO is idling, LED0 is on.


Feel free to try and recreate this project.  For low-light conditions, try using another non-inverting amplifier to further increase the voltage reading.


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