Use the KeyPress event of a text box to capture the KeyAscii of each typed character. Then do something like:

VB Code:
  1. intAscii = KeyAscii
  2.  
  3. If intAscii > 128 then
  4.   strBinary = 1
  5.   intAscii = intAscii - 128
  6. Else
  7.   strBinary = 0
  8. End if
  9.  
  10. If intAcii > 64 Then
  11.   strBinary = strBinary & 1
  12.   intAscii = intAscii - 64
  13. Else
  14.   strBinary = 0
  15. End if
  16.  
  17. etc...

or to shorten it up you can do:

VB Code:
  1. intAscii = KeyAcii
  2. intCurrent = 128
  3.  
  4. For i = 1 to 8
  5.   If intAcii > intCurrent then
  6.     strBinary = strBinary & 1
  7.     intAcii = intAcii - intCurrent
  8.   Else
  9.     strBinary = strBinary & 0
  10.   End if
  11.   intCurrent = intCurrent / 2
  12. Next

Hope this helps.