Hi Siddharth,

If I was in your place I would never connect the output of OmAmp LM324 to INTx pin of CPU. Even if it is a comparator. I avoid such designs. I had suffered a lot of sleepless nights because of this. I don't know the reason, and I do not want to know it either.

In your case, you are using IR sensor to trigger the OpAmp. Now there are many sources of IR, examples: your IR Transmitter, Fluorescent tube lights, reflections from walls, TV remotes, some heaters/ovens and reflections from them,etc....You cannot control all those coming to your IR sensor. But you use an opaque tube sleeve to cover the sensor from taking signals from other sources, set the direction of the sleeve so that it can take IR light from the transmitter only.

You can also try by changing your ISR, to count the number of interrupts and show them on the screen. Now switch OFF your IR transmitter, and note the number of interrupts, if it is increasing, then you are recieving signals from other IR Sources, or there is something wrong in your circuit.

And yes, You have to add hysteresis to your Comparator (as suggested by other members) so that the circuit works properly.