o
      |
      |
     +-+
     | |R
     | |
     +-+
      |           1+--------+2   +----------------
 +----+----+-------+Schmitt +----+ AVR 
 |         |       |Trigger |    | (z.B. PortA0)
 +-       ---C     +--------+    |
   /      ---       74HC14       |
  / T      |                     |
 |         |
---       ---

für Entprellzeit von 50ms: R=50kOhm; C=1µF