Robin2:
I don't know what you mean by "without that is not working"...R
this is oart of your code.
I mean what if you remove the one second waiting time to show data?
void loop() {
getIsrData();
// (millis() - prevDisplayMillis >= 1000) {
// prevDisplayMillis += 1000;
showData();
// }
}
pulses per second will not be true if you unable those lines!