labsw/: added low-pass filters to button input (with help from Joerg Reisenweber)

labsw/LOG

@@ -221,6 +221,8 @@ To do: debounce buttons (in software) before accepting a state change.
   - added external pull-ups to IN_* and to buttons (so that we can turn
     off the internal pull-ups and thus avoid sneak current through the
     opto-coupler LEDs from VBUS via the pull-ups into VDD)
+  - added low-pass filters to button inputs, to suppress interferences,
+    e.g., from load being switched (with help from Joerg Reisenweber)
 
 Pending:
 - widen column cavities by 0.2 mm on each side