How to subtract micros()?

Question

I am attempting to calculate the time between pulses by comparing the micros() timestamp. I understand that you cannot just simply subtract unsigned longs, but I cannot understand what the alternative for it is.

Below is a simplified version of code. On pin 6 I receive 2ms long pulses every 2ms comparing the times returns "-19728". I'm planning to make the pulses much shorter once I figure out this math problem.

Site note: I'm using pulses to make two Arduinos send simple data via digital pins.

Thanks you.

int pinReceiver = 6;
int val = 0;
int isReceiving = 0;
int pauseLength = 0;
unsigned long timeStart = 0;
void setup() {
 Serial.begin(9600);
 pinMode(pinReceiver,INPUT); 
}
void loop() {
 noInterrupts();
 val = digitalRead(pinReceiver);
 if(val==HIGH){
 if(isReceiving==0){ //Pulse begins
 isReceiving = 1;
 pauseLength = micros() - timeStart;
 Serial.println(pauseLength);
 }
 } else {
 if(isReceiving==1){ //Pulse ends
 isReceiving = 0;
 timeStart = micros();
 }
 }
 interrupts();
}

• chrisl: The calculation seems correct. Please try to also use unsigned long for pauseLength. That might be your problem
• Andi Stancu: That definitely solved the problem. I assumed that since the difference would be such a short number it could be int. Thank you. I don't know how to mark this as solving answer.
• chrisl: I think its more about that you mixed unsigned and signed types. Tomorrow I will write an answer, that you can accept
• jsotola: what happens if you cast long to int ? ... pauseLength = (int)(micros() - timeStart)

Answer 1

Long to Integer conversion will overflow the value and you'll get values in negative numbers.

Define the pauseLength as unsigned long to make it work.