Switches

• basic two-position switch
• momentary switch
• foot pedal
• roller switch
• mercury switch (binary tilt)
• burgular alarm switches (optical, magnetic, ...)
• multi-position switches ... need different approach than described here

Interfacing Switches to the BASIC Stamp:

• Two-position switches must produce voltages between 0 - 5 Volts, about a threshold of approximately 1.5 Volts.

  

• Read pin value using INS register:

'{ $STAMP BS2 } INPUT 0 'make I/O pin 0 an input loop: PAUSE 400 'sleep for 400 milliseconds IF IN0 = 0 THEN low 'pin high ... so something GOTO loop low: 'pin low ... so something GOTO loop

• Use the BUTTON routine, which provides "debouncing" and auto-repeat functionality:

  BUTTON Pin, DownState, Delay, Rate, Workspace, TargetState, Address

  where:

  • Pin is I/O pin switch/button is connected to.
  • DownState specifies switch/button "down" state (0 or 1).
  • Delay specifies delay before auto-repeat, in cycles of the BUTTON routine (0 - 255). If Delay = 0, no debounce or auto-repeat. If Delay = 255, debounce but no auto-repeat.
  • Rate specifies number of cycles between auto-repeats, in cycles of the BUTTON routine (0 - 255).
  • Workspace is a byte variable used by BUTTON (must be zero before use and not adjusted outside BUTTON command).
  • TargetState specifies when branch should occur (0=not pressed, 1=pressed).
  • Address specifies where to branch if switch/button is in target state.

  '{ $STAMP BS2 } nouse VAR BYTE 'workspace variable for BUTTON instruction loop: BUTTON 0, 0, 255, 250, nouse, 0, nopress 'branch to nopress unless pin0 = 0 DEBUG "* " nopress: GOTO loop