Microcontroller measures heart rate through fingertip

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Step 2: Signal conditioning circuit

Picture of Signal conditioning circuit
The reflected IR signal detected by the photo diode is fed to a signal conditioning circuit that filters the unwanted signals and boost the desired pulse signal. The circuit diagram above shows the IR LED (D1) and the photo diode (D2) along with the signal conditioning circuit made of two stage operational amplifiers configured as active low pass filters. The cut-off frequencies of both the filters are set to about 2.5 Hz, and so it can measure the pulse rate up to 2.5*60 = 150 bpm. The gain of each filter is about 100, which gives the total 2-stage amplification of 10000. This is good enough to convert the weak pulsating signal into a TTL pulse. Note that at the input of each OpAmp filter stage, there is a 1 uF capacitor to block any DC component in the signal. At the output is connected a LED that will blink with heart beat. The cathode of LED gets the ground path through the collector of BC547 transistor. In order to save the battery life, the transistor is turned on for 15 seconds by PIC16F628A microcontroller while the measurement is going on. The number of pulses counted within this interval is multiplied by 4 to get actual beats per minutes (bpm).  
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himanshu_33755 months ago

hey, i have tried several times but failed to achieve this. can u please help me out?? can u please send me all the details with the program codes?

if possible please send me on

that is fancy, l like the master piece. sir what culd be the possible project code for this and how is it implemented? email; thank you.
longjasp2 years ago
Can i use pic basic language for the code?
longjasp2 years ago
can i get the code for this project? very nice idea,. pls email me thnk u.
jayati3 years ago
your project is fascinating..if i try to implement it, will the IR sensors be able to detect such a small change in blood volume...practically? Or are there any better sensors available for this project??
Sir please reply sooon..