___________________
_______+___|\                           |                   |
           | \                     R1   |                  | | R2
           | 1\__________   ____------__|______|\          | |
   ___-____|  /       |  \  |   ------         |-\          |
   |       | /       | |  \ GND                |  \         |
   |       |/        | |   \                   |   >________|__________
   |                  |     \     R3           |  /
   |__________________|      \__------_________|+/
                      |         ------      |  |/
                     | |                   | |
                     | |                   | |R4
                      |                     |
______________________|_____________________|__________________________