debouncing switches with a timer interrupt?

[Charles Linquis]

The code below was written to use a momentary pushbutton switch as an ON/OFF control.

It is written to be used in a Timer interrupt routine.

PowerOnDelayTimer is the number of interrupts that the button must be held before turning ON the unit.

PowerOFFDelayTimer is the number of interrupts that the button must be held before turning OFF the unit

SwitchUpDelayTimer is the number of interrupts that must expire before the button can be pushed again (useful when you don't want someone rapidly turning ON and OFF a piece of hardware).

            IF !EnableSw THEN     ; Aliased pin, goes low when button pushed.
                 
                 IF SwitchFlag THEN ; Switch has been pushed, but prevously released.
                                               
                   IF PowerSwitchCounter < 250 THEN 
                           PowerSwitchCounter = PowerSwitchCounter + 1  ; don't let it overflow
                   ENDIF 
                        
                                              
                   IF PowerONstate = 0 THEN  ; Currently OFF
                       If PowerSwitchCounter >= PowerOnDelayTimer then           ; Turn on or off
                          Gosub PowerOn
                          SwitchFlag = 0
                          SwitchUpCounter = 0
                       ENDIF 
                    ELSE      ; Currently OFF
                       If PowerSwitchCounter >= PowerOffDelayTimer then  
                         GOSUB PowerOff
                          SwitchFlag = 0
                          SwitchUpCounter = 0
                      ENDIF
                   ENDIF
       
                ENDIF
      
            ELSE
                IF SwitchUpCounter < 250 THEN 
                      SwitchUpCounter = SwitchUpCounter + 1
                ENDIF      
                IF SwitchUpCounter > SwitchUpDelayTimer THEN 
                     SwitchFlag = 1          ; Switch has been released
                     PowerSwitchCounter = 0 
                ENDIF      
           ENDIF