Hi! I need some ideas for my bradycardia and tachycardia sensor. It is part of a university project for an incubator prototype, it has to activate some kind of alarm (buzzer or LED) whenever the baby's pulse is not between the normal pulse range. The parameters that I have to take into account is that, for a baby, bradycardia occurs below 80 bpm and tachycardia above 150 bpm, that is a given fact that the sensor shall detect. My basic idea is to use a pulse sensor made from an IR and a phototransistor that will give a signal in a certain frecuency. I did some research and what most people do is to connect that pulse sensor to an amplifier to increase the signal, then it is filtrated by an active band pass filter and finally it is amplified one last time and it gets to an Arduino. I CANNOT USE ANY KIND OF DIGITAL CIRCUIT, JUST ANALOG. My idea is that if I make a band stop filter, instead of a band pass filter, I can eliminate the frecuencies in which the baby is okay, so if in any case the pulse goes out from the range the filter will give a signal. Then, I was thinking of connecting the resultant signal of the filter to a comparator made form op-amp. In which case will have the function of activating the alarm. If the frecuency is in the range (1.33Hz - 2.5Hz) it will not activate the alarm, if the contrary happens, it will activate the alarm. I'm not pretty sure if it will work or if it's another way to do it. As I said, I'm not allowed to use Arduino or something related to digital electronics. I attached my circuit, thank you!