2 Heart Beat Counter

As the heart beats, it delivers blood from (or to) the heart to the rest of the body. It is believed that as the blood flow to your veins, you skin light reflectivity varies since blood density affects skin reflectivity especially infrared (IR) lights. The simple circuit below will help us count the number of heart beat. The output pin can be connected to microcontrollers or computer to monitor the count.
schematic diagram
Positioning IR Emitter and Receiver
Part List:
R1 - 120 ohms 1/4W
R2 - 330 ohms 1/4W
POT1 - 10 kilo ohms potentiometer
LED - Infrared (IR) LED
Q1 - SY32PT or similar Phototransistor
Q2 - 2N2222, 9013, or similar NPN transistor


  1. great project but i have question about SY32PT IR photo transistor which is : i didnt find that number of phototransistor but i found another one wihch is similar to it but it have 3 terminals and the previous has 2 why this differnce and what does the third terminal corresponds to ?

  2. Can i connect an LED to the output to get the blinks ?