My goal is that I can capture data sending to my Uno board when there is a HIGH (when the control voltage at pin#2 is greater than 3V) and keep capture the data till the the control voltage drops below 3V.
Since the UNO doesn't support HIGH mode in the attachInterrupt but Arduino Due, Zero, MKR1000 only and the other Modes doesn't quite appropriate in my application, I wonder if you have any recommendation or suggestion for the problem.
If you are going to use interrupts on the UNO for your task, use CHANGE, and read the state of the pin in the ISR. If it went high, start your data capture, if it went low, end your data capture.
You will have to provide more information about the "data capture". It's not likely that you will be able to do the data capture within the ISR. You may have to set a flag in the ISR and make sure that your program is non-blocking and tightly looped.
Cattledog, you're right. HIGH on Uno means CHANGE. I did use it for my code till to your posts enlightened me.
Robin2 and 6v6gt, thanks for your suggestions. The period of time that the system collects data is up to users, it could be 1 second till to infinitive. I have no idea why I used the interrupt, and I should just use a digitalread and if/else statement to get the job done.