Hello everyone, I can't figure out why the external interrupt via the attachinterrupt() function on my arduino uno is not working. I'm using a National Instruments card to send the arduino an analog TTL (5V) pulse into digital pin 2 or 3. Per the instructions, I am using the 0 interrupt designation for digital pin 2. I've tried using pin 3 as well. Even the example code provided in the reference doesn't work. Reference code: http://arduino.cc/en/Reference/AttachInterrupt
Are there some special requirements for the TTL pulse? Any thoughts? I'm stumped.