from time import ticks_ms, ticks_diff
from machine import Pin
# variables
interrupt_flag = False
pre_peak = ticks_ms()
curr_peak = ticks_ms()
# Read the voltage from Pin 26
comp_in = Pin(26, Pin.IN, Pin.PULL_DOWN)
# ISR function
def callback(comp_in):
    global interrupt_flag, pre_peak, curr_peak
    pre_peak = curr_peak
    curr_peak = ticks_ms()
    interrupt_flag = True
# create external interrupt
comp_in.irq(trigger=Pin.IRQ_RISING, handler=callback)
while True:
  try:
    if interrupt_flag :
      interrupt_flag = False
      # print(f"Peak: {curr_peak} with previous: {pre_peak}")
      diff = ticks_diff(curr_peak, pre_peak)
      if diff > 270 and diff < 1500:
          BPM = int(60*diff/1000.0)
          print(f"BPM = {BPM}")
  except KeyboardInterrupt:
    break
print("Finished")