Reading FAN tachometer/RPM on 4 wire fan using arduino I am following the wiring and code at https://playground.arduino.cc/Main/ReadingRPM but using pin 9 to read the speed instead of pin 2 and I have added a 10K pull up resistor between pin 9 and +5V as well; I dont see any interrupts firing even though the fan is running;

The fan is a standard intel cpu fan with 4 wires(black, yellow, green, blue) and the green wire is the sense/tach wire and I have connected it to pin 9 as well;

Need some help or expert advise; I am not sure if the approach works fine or not;
There are no interrupts on pin 9 (unless you are using Pin Change interrupts...?). You have to use pin 2 (interrupt 0), or pin 3 (interrupt 1) (also, on the Mega: 18 (interrupt 5), 19 (interrupt 4), 20 (interrupt 3), and 21 (interrupt 2)).