It’s code time… I’ve been cutting and pasting code together trying to get everything to work at the same time. I’m using a em-406a GPS on the Adafruit GPS shield. I have 2 photogates that need to use the attachinterupt() function. The only digital pins that are setup on the Arduino UNO for attacheinterupt() are 2 and 3. The GPS shield uses digital 2 and 3 for GPS communication using NewSoftSerial. So I tried moving the GPS to other pins, 8 and 9 worked. Now pins 2 and 3 are free for my photogates.