Re : Heart Rate monitor using infared LED

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


Regards

Ken

 

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.