Photoplethysmogram (PPG) signal time period measurement


I am working on a project that measures the heart rate in b.p.m. For this I am planning to use Arduino UNO. A PPG signal is basically a quasi-sine wave which needs to be filtered prior to measuring time period just for simplicity's sake.So, the PPG signal is passed through a peak detection circuit and a square wave whose voltage varies from -4V to +4V is resulted whose time period is to measured. Can someone please help me with finding the time period of the resulting square wave using arduino UNO? Any help is much appreciated.

Thanks in advance

utilise the interrupt perpheral on the Arduino UNO there are 2 hardware interrupts you need one to acknowledge the pulse that is generated and then calculate the difference between 2 pulse occurences.