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  1. #1
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    heartbeat sensor

    hai everybody
    now iam working with a heart beat monitoring project in p16f877a...finger is used to detect the heart beat count....but it doesnt give actual count ..in one minits its counts more than 256...if we not place finger in sensor part its give proper count means '0'..but wen we place the finger between high intensity red led and ldr count is more than 256..i think fluctuations in the finger affecting the sensing part.. i dont know how to attach circuit diagram iam using LM358 and the 7th pin of lm358 is the sensor output ..iam connecting the 7 th pin to a ledand also to PORTC0 PIN BUT IAM NOT USING ANY PULL UP IN PORTCO PIN....CAN U PLAESE HELP ME TO SOLVE THIS PROBLEM
    THIS IS THE CIRCUIT DIAGRAM LINK http://onlinetps.com/heartbeat.GIF


    thankzzzzzzzzzzzzz in advance

    •   Alt30th December 2008, 09:00

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  2. #2
    FvM
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    heartbeat sensor circuit

    It's a bad circuit to my opinion, but I didn't hear a word about you trying to adjust the sensor's sensitivity, as obviously necessary with that circuit.



  3. #3
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    lm358 heartbeat

    thaaankz............
    ya iam trying to adjust the sensor lots of time and some times i got aproximate count..but it not constant ..and now iam given a 100uf capcatior and a pull up in the output pin of lm358 that connected to Portc0..the output is better than old...but some times its varying



    •   Alt30th December 2008, 10:47

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  4. #4
    FvM
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    sensor circuit using lm358

    Don't understand, how you connected the capacitor. A pullup resistor shouldn't change anything, cause LM358 has a push-pull output.



  5. #5
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    lm358 finger

    pullup in Rc0..and 7th pin of lm358 connected to a capacitor +ve pin and -ve to gnd(100uf)



  6. #6
    FvM
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    better than lm358

    A rather brute circuit to my opinion. A more versatile solution would be using a linear AC amplifier with a gain of 10 to 100 and the PIC ADC as a programmable threshold detector. It would allow for automatic gain control and similar features.



  7. #7
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    heart beat circuit diagram

    I agree with FVM that its a bad design as it depend on the LDR.
    It will never be accurate.
    In my humble view "find the alternate circuit".



  8. #8
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    Re: problem with heart beat sensor

    I know its old post but many of us want to make something related to heart beat sensing here i found simple circuit
    Heartbeat Sensor (Tranduscer) | Circuit Diagram



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