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Re : Heart Rate monitor using infared LED

Discussion in 'Electronic Basics' started by Support, Jun 28, 2004.

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  1. Support

    Support Guest

    Hi there,

    I am wondering whether is there a Simple schematic for a Heart Rate monitor
    using infared LED.

    My idea is to design a simple heart rate monitor which detect heart pulses
    by placing the finger over a pair of Infared LED (one receiev and one
    transmit side by side) . The signal captured will turn ON or OFF a LED ...I
    think is similar to a pulse oximeter.

    Any help or suggestion is appreciated


  2. You should use an LED and a photo transistor or photo diode.
    This is basically a signal to noise problem. So you want to exclude
    as much information from the detected signal as possible that is not
    likely to be directly related to heart rate. This means that the
    average DC level of the signal must be ignored, along with all AC that
    is outside the frequency range expected for heart rate. So, before
    you can apply lots of gain to pull the weak signal out of the noise
    (which would saturate on the noise), you need a bandpass filter. Then
    you use a comparator with a bit of hysterisis, perhaps, to turn on the
    LED when the signal is more than zero and turn it off when the signal
    is less than zero. Keeping most of the ambient light out of the
    detector helps a lot, too.
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