chronograph

Projects General Guidance
1

I'm making a chronograph using two strips of aluminum foil placed 1 foot apart, the idea is to measure the time from when the first strip breaks to when the second strip breaks. sounds simple but I can't seem to get it to work. I set up a test circuit to manually test it by simply disconnecting one wire then the other, but it only gives me a 0 , -2147483648, or -1. Any help I could get would be greatly appreciated.

const int trip1 = 4;
const int trip2 = 5;

int trip1state = 1;
int trip2state = 1;
long timestart =0;
long timestop = 0;
long totaltime = 0;
int fps = 0;
float timeinseconds;

void setup() {
  pinMode (trip1,INPUT);
  pinMode (trip2,INPUT);
  Serial.begin(9600);
}

void loop(){
  while (timestop==0){
  if (digitalRead(trip1) == LOW){
    timestart = micros();
  }
  if (digitalRead(trip2) == LOW){
    timestop = micros();
    totaltime = timestart - timestop;
    timeinseconds = totaltime / 1000000;
    fps = 1/timeinseconds;
    Serial.println(fps);
  }
  }
}
2

You are testing for signal levels, not for signal transitions which is what you need to do. So as soon as the first strip breaks your code is continuously reseting starttime from then on.

You need to wait for the first strip to break, and then go on to test the second strip - not process both in pseudo-parallel:

Something more like this should help:

void loop()
{
  while (digitalRead (trip1) == HIGH) {} // wait for first strip to break
  timestart = micros () ;
  while (digitalRead (trip2) == HIGH) {} // wait for second strip to break
  timestop = micros () ;
  totaltime = timestart - timestop;
  timeinseconds = totaltime / 1000000.0 ;
  fps = (int) (1.0 / timeinseconds) ;
  Serial.println(fps);
  while (digitalRead (trip1) == LOW || digitalRead (trip2) == LOW) {} // wait for sensors to be reset
}

I've also fixed the integer divide to be a float divide so the answer isn't just zero.