debouncing switches with a timer interrupt?

[aratti]

This would still require some kind of debouncing. The logic state can "bounce" a number of times when pressing a button

Contact's debouncing should be solved with proper RC filter! If proper filtering is not possible an additional IF/THEN statement should reduce greatly the debouncing effect.

False        CON  0
True         CON  1
KEYPRESS  VAR portXx
KeyFlag      VAR BIT
Counter      VAR WORD

LOOP:

PAUSE 1

IF KEYPRESS = False then

IF KeyFlag = False Then
Counter = Counter + 1
KeyFlag = True
ENDIF

ELSE
KeyFlag = False
IF  KEYPRESS = False THEN  KeyFlag = True    ' re-checks the key logic state
ENDIF
.
.
.
.
.
GOTO LOOP

Al.

[DDDvvv]

thanks guys.

i tried the capacitor method, and that did not work well. still skipping menu items.

im using proteus simulation, and i tried every value of cap, 1000uf to 0.000001 uf., and everything in between.

ill try integrate the software flag idea into the problem, and hope that it fixes it. thanks

[DDDvvv]

hi all
i tried to implement the flag idea, but still the same result. menu item cycles through 3 to 6 items with one push of a button. here's the code snippet

RB_MainMenuLoop:
' BTN_PLUS is the Next Choice button
    PAUSE 1
      IF BTN_PLUS=0 THEN
      ;PAUSE 200
      IF FLAG_PLUS = 0 THEN
      bMenuPos=bMenuPos+1
      FLAG_PLUS = 1
      ELSE 
      FLAG_PLUS = 0
      IF BTN_PLUS = 0 THEN FLAG_PLUS = 1
      ;ENDIF
      IF bMenuPos>22 THEN
         bMenuPos=1
      ENDIF
      ENDIF
      Goto DisplayMainMenuLoop:
   ENDIF

im beginning to think that debouncing is not the problem. is there any other way to skin this cat?

[aratti]

Counter Var Byte

RB_MainMenuLoop:
' BTN_PLUS is the Next Choice button

PAUSE 1

IF BTN_PLUS=0 THEN

IF FLAG_PLUS = 0 THEN
bMenuPos = bMenuPos + 1
FLAG_PLUS = 1
Counter = 0
ENDIF

ELSE
Pause = 10
Counter = Counter + 1
IF Counter > 50 THEN FLAG_PLUS = 0 : Counter = 0
ENDIF

IF bMenuPos>22 THEN
bMenuPos=1
ENDIF

Goto DisplayMainMenuLoop:

================================================== ===============

Try this snippet and see how it works. You can tune the PAUSE 10 and Counter > 5, to better values to suite your need.

Al.

[Acetronics2]

hi all
i tried to implement the flag idea, but still the same result.

Hi,

You should understand debouncing NEED time, where ever this time comes from ( capacitor, timer ...)

the idea of debouncing is :

" Does the electrical state of pin still changes afer X milliseconds ??? "

so, you can't get a correct answer before X milliseconds !!! - Obvious -

But 200 ms is debouncing time for really poor quality switches, 20 ms can be obtained easily.

note also switches " bounce " when closing its contact ... not when opening it !!!

so, ... is it here THE good idea ???

Further, May I tell you a real time timer might not be disturbed by a keypress ... - or your program is " not so good " ...

the delay needed by the RTC to be updated is so far smaller than a key press action ...

Alain

[Mike, K8LH]

Consider using a switch state latch and relatively simple logic to sample your switches and detect the "new press" state while ignoring the other switch states. Here are the switch states;

swnew swold  switch state
  1     0    a "new press"
  1     1    still pressed
  0     1    a "new release"
  0     0    still released

Sample the switches at a decent debounce interval (16 to 25 msecs) either in your main program loop or in a timer based interrupt service routine. You only need a few lines of code to implement the switch state logic for multiple switches (perhaps one of the PBP gurus can interpret the C code? Sorry!);

//  swnew  ____---____-----_____   new switch sample
//  swold  _____---____-----____   switch state latch
//  delta  ____-__-___-____-____   changes, press or release
//  newhi  ____-______-_________   filter out release bits
//

while(1)                  //
{                         //
  delay_ms(24)            // 24-msec debounce interval
  swnew = ~porta;         // sample active-lo switches
  swnew &= 0x0F;          // on RA3..RA0 pins
  swnew ^= swold;         // changes, press or release
  swold ^= swnew;         // update switch state latch
  swnew &= swold;         // filter out "new release" bits
  if(swnew)               // if any "new press" bits
  { beep();               // task a "new press" beep
  }
  
  if(swnew.0)             // if RB0 "new press"
  {                       //
  }                       //

  if(swnew.1)             // if RB1 "new press"
  {                       //
  }                       //
}

If you implement the method in an ISR you'll need to inclusive-or "swnew" with a "flags" register for your main program.

Kind regards, Mike

[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

[Charles Linquis]

I should state that SwitchFlag must be initialized to a non-zero value at the top of the program.

[Mike, K8LH]

I'd like to supplement Charles' fine example with an interrupt driven version of the "parallel switch state logic" example I posted earlier.

This example uses a 1-msec timer driven interrupt "heart beat" which is perfect for toggling a piezo speaker at 500-Hz and it uses a simple counter to produce a 32-msec debounce/sample interval.

Using a momentary switch to emulate a "toggle" switch (press to toggle from on-to-off or from off-to-on) can be accomplished directly by the driver by exclusive-or'ing the debounced "new press" bits with the "flags" switch flag bits variable. Main should test the switch flag bit and then clear it for "momentary" switches or simply test the switch flag bit for an emulated "toggle" switch.

void interrupt()                // 1-msec Timer 2 interrupts
{ 
  pir1.TMR2IF = 0;              // clear TMR2 interrupt flag
//
//  beep task (32-msec 500-Hz tone using 1-msec interrupts)
//
  if(beep)                      // if beep task running
  { spkrpin ^= 1;               // toggle speaker pin and
    beep--;                     // decrement beep msec counter
  }
//
//  switch state management (multi-switch "parallel" logic)
//
  if(--dbcount == 0)            // if 32-msec debounce interval
  { dbcount = 32;               // reset debounce timer and
    swnew = ~porta;             // sample active low switches
    swnew &= 0x0F;              // on RA3..RA0 pins
    swnew ^= swold;             // changes, press or release
    swold ^= swnew;             // update switch state latch
    swnew &= swold;             // filter out "new release" bits
    flags ^= swnew;             // toggle flag bits for 'main'
    if(swnew)                   // if any "new press" bits
      beep = 32;                // task a "new press" beep
  }
}

//  in "main"

  while(flags.0)                // while sw0 (RA0) "on" (toggle), do this block
  {                             // until new sw0 press toggles flags.0 to "off"
    if(flags.1)                 // if sw1 (RA1) "new press" (momentary)
    { flags.1 = 0;              // turn off flag and
      ...                       // do something
    }
  }