Record an ever changing cells value from Sheet 1 every 30 seconds into Sheet 2

Try this macro:

Public Sub test()
Dim Start As Variant, asd As Integer
Start = Timer
asd = 1
Do Until Sheets("Sheet1").Range("A1") = "BYE"
  Sheets("Sheet2").Cells(Rows.Count, 1).End(xlUp).Offset(1, 0) = Range("A1")
  Do Until asd = 0
  DoEvents
  asd = Int(Timer - Start) Mod 30
  Loop
  asd = 1
Loop
End Sub

First of all, I must apologize as there is a problem witht he first macro I published. Here a modified macro that works well:

Public Sub test()
Dim Start As Variant, asd As Integer
Start = Timer
asd = 1
Do Until Sheets("Sheet1").Range("A1") = "BYE"
'This is to be able to stop the macro by entering the word BYE inthe cell A1
  Sheets("Sheet2").Cells(Rows.Count, 1).End(xlUp).Offset(1, 0) = Sheets("Sheet1").Range("A1")
'Here, it takes the value of cell A1 from Sheet1 (right part of equation)
'and copy it to the first empty cell in column A of Sheet2.
'You can change the cell under scope by changing the reference A1 by the cell addrress you want.
'
'This loop if there to wait 30 seconds. You can change the 30 to the number you want
  Do Until asd = 0
  asd = Int(Timer - Start) Mod 30
  DoEvents
  Loop
'This loop is to wait till the end of the 30st second to write the data
'Otherwise, process is so fast, it would write thousands of duplicates within this second.
  Do Until asd = 1
  asd = Int(Timer - Start) Mod 30
  Loop
Loop
End Sub

I added some comments so you know what a line of program does.
Look at the attached file for a working workbook.
Hope this helps