Projects -- Interrupts: Mark II

/*
 * Project:      Project_interrupt
 * Author:      Jane-Maree Howard
 * Date:         Monday 21/11/2011
 * Platform:    Arduino 22
 * Purpose:    To demonstrate an interrupt on Digital pin 3
 * Operation:  Description: Connect a 20kilOhm resistor from
 *                          digital pin3 to digital pin13!
 *                          Earlier problem solved as we now have a hardware feedback
 *                          from OUTPUT digi-pin13 to INPUT digi-pin3,
 *                          to which the interrupt is attached.
 *                          The digital flip-flop occurs every second, is fed to digi-pin3,
 *                          which registers the change & triggers the interrupt,
 *                          which, in turn, calls blink() where the pin state variable is flipped.
 *                          This state change is fed back via digi-pin13 to digi-pin3, triggering
 *                          the interrupt once again.                 
 */
int           iPin13   = 13;
int            iPin3   = 3;
volatile int  iState   = LOW;

void setup()
{
  // open Serial port
  Serial.begin(9600); 
  // set pin13, pin3 as OUTPUTs
  pinMode(iPin13, OUTPUT);
  pinMode(iPin3, INPUT);
  // interrupt1 calls blink() when pin13 flip-flops
  attachInterrupt(1, blink, CHANGE);
  digitalWrite(iPin3, iState);
  Serial.println("\nStart\n");
}//setup()

void loop()
{
  // delay 1 second
  delay(1000);
  // in effect, flip pin13
  Serial.println(iState);
  digitalWrite(iPin13, iState);
  digitalWrite(iPin3, iState);
}//loop()

void blink()
{
  // flip value to trigger interrupt
  iState = !iState;
}//blink()
//END

i finally cracked it!

most annoying though..
..but when i wondered about which pin the interrupt operated on, i went back to the appropriate page.. 

..where i saw that interrupt-0 can be attached to digital pin 2, & interrupt-1 to digital pin 3.

after that, it was pretty much plain sailing - the feedback resistor instead of some weird software, & as can be seen at left, it works beeootifly-thank-yew!

on to my next problem: how can i use LDR hardware to trigger an interrupt (for my "fridge door open" stuff!

{sigh of relief!}.