+---------+-----------+---------------------------------------------------------------------+---------------+    5V
          |           |                                                                     |
          |           |                                                                    +++
          |          +-+                                                                   | |
          _          |-|                                                                   | | R3=1k
          ^          |-|  R1=120                                                           +++
          |          +-+                                                                    |
          |           |                                                                     |
          |           |                                                                     |
          |           |                                  Messpunkt                          +-----------+----+   GPIO2 (3,3V)
   +--------------------------------+----+--------------                                    |           |
          |           |             |    |               GPIO1 (3,3V)                       |           |
          |           |             |    |                                                 +++          |  +
          |           |             |    |                                                 | |          |->+
          |          +-+            |    |                    XXXXXXX   S1 Reedkontakt     | | R4=2k       |   OK1
          |          |-| R2=220     |    +------------------XXX    +----+                  +++            /|
          _          |-|           ---                                  |                   |            / +
          ^          +-+           ---   +------------------------------+                   |           /
          |           |             |    |     30 m                                         |           |
          |           |         C1  |    |                                                  |           |
          |           V        10µF |    |                                                  |           |
          |           _  OK1        |    |                                                  |           |
          |           |             |    |                                                  |           |
+---------+-----------+-------------+----+--------------------------------------------------+-----------+---+     GND