How can i measure pulse width? (2 interrupts)

Forum 2005-2010 (read only) Software Syntax & Programs
1

I need to measure pulse width (not time between two pulses, but length of one single pulse - from raising to falling) on fuel injector - it is driven by simple square pulse on ground wire (positive wire is allways attached to battery's +)
Can i assign TWO interrupts to ONE pin? i tried this:

int injPin = 3; //Pin connected to injector's ground wire
volatile unsigned long injTime1;  //Time of front raising
volatile unsigned long injTime2;  //Time of front falling
unsigned long injTime;

void setup()
{
  pinMode(injPin, INPUT); 
  digitalWrite (injPin, HIGH);  //Pull-up pin - as our injector is driven by connecting it to ground, i suppose i need to pull-up pin to get it's value as 1 when injector is turned off
  attachInterrupt(1, up, RAISING);  //interrupt on raising front
  attachInterrupt(1, down, FALLING);  //interrupt on falling front
}

void loop()
{
 //some code
}


void down()
{
 injTime1 = micros(); //get time of pulse going down
}
void up()
{
  injTime2 = micros();  //get time of pulse going up
  injTime = injTime2 - injTime1;  //measure time between down and up (so it will be time between ground appearing ot pulled-up pin, and ground disappearing)
}

but my "down" (on falling) interrupt didn't fired even when i removed pull-up - can i use 2 interrupts on 1 pin, or i need to shortcut another interrupt-enabled pin (pin 2 to pin 3) and use two pins for two interrupts?

maybe someone will purpose some simple external logic to measure pulse width?

thanks! :slight_smile:

2

As you've discovered, two interrupt conditions cannot be attached to one pin. Instead, use a CHANGE interrupt and simply check the condition of the pin in your interrupt service routine.

3

Oups :-[
Thanks a lot!
So looks like i need this:

int injPin = 3; //Pin connected to injector's ground wire
volatile unsigned long injTime1;  //Time of front raising
volatile unsigned long injTime2;  //Time of front falling
unsigned long injTime;

void setup()
{
  pinMode(injPin, INPUT);
  digitalWrite (injPin, HIGH);  //Pull-up pin - as our injector is driven by connecting it to ground, i suppose i need to pull-up pin to get it's value as 1 when injector is turned off
  attachInterrupt(1, pik, CHANGE);  //interrupt on front changing
}

void loop()
{
 //some code
}

void pik()
{
 if (injPin == LOW) //Or i need to digitalRead it first?
 {
  injTime1 = micros(); //get time of pulse going down
 }
 else
 { 
  injTime2 = micros();  //get time of pulse going up
  injTime = injTime2 - injTime1;  //measure time between down and up 
 }
}

hope it will work, will try it in a couple of days :sunglasses:

4 
int injPin = 3; //Pin connected to injector's ground wire
[glow]volatile [/glow]unsigned long injTime; [glow]// When accessing this in setup or loop (or anything called by either) interrupts must be disabled[/glow]

void setup()
{
  pinMode(injPin, INPUT);
  digitalWrite (injPin, HIGH);  //Pull-up pin - as our injector is driven by connecting it to ground, i suppose i need to pull-up pin to get it's value as 1 when injector is turned off
  attachInterrupt(1, pik, CHANGE);  //interrupt on front changing
}

void loop()
{
 //some code
}

void pik()
{
 [glow]unsigned long injTime1;  //Time of front raising[/glow]
 [glow]unsigned long injTime2;  //Time of front falling[/glow]

 [glow]if ( digitalRead( injPin ) == LOW ) //Or i need to digitalRead it first? YES.[/glow]
 {
  injTime1 = micros(); //get time of pulse going down
 }
 else
 {
  injTime2 = micros();  //get time of pulse going up
  injTime = injTime2 - injTime1;  //measure time between down and up
 }
}
5

Thanks a lot for your remarks! :slight_smile: