Check In/Check Out by Item Number

I have tried to approach this from a few different angles, but the formulas get really convoluted really quickly. I wanted to see if someone had a fresh idea that I could benefit from.
Basically, we will have a bar-code scanner adding values into column A of sheet 2. I need sheet 1 to populate when an item number is added to sheet 2 such that, the first time that item number comes up, it fills out a new row on column A and the second time that item number comes up, it populates in the same row, column B. The item numbers cycle through and are reused on the same workbook, however, so I'll need a fresh row to populate when that same item number is entered a 3rd time, etc. There will be 240 rows of checking in and out per workbook and there's no guarantee to what order they will be scanned in/out. I'm hoping I presented this in a clear enough way to promote ideas. I appreciate any help you can provide!

I think if you can look for inventory system template published, there is lot free, that can take some idea or template most match from you want and can post here to modify it