debouncing switches with a timer interrupt?

[Charles Linquis]

Could it be that you don't need a debouncer at all?

If you are polling the pin that is connected the switch every program loop, and the loop is longer than the switch bounce time, you don't need a debounce, since it will see the transition, and the "bounces" will be over before you check the switch again.

[Dave]

Charles, I do just exactly that. In my interrupt routine. I copy th state of my button and add it to a shifted result. When the button is connected to ground with a pullup to VDD, the value after the 8 cycle (interrupt) debounce is equal to zero. When the button is released the value after the 8 cycle (interrupt) debounce is equal to 255. I use a 10 millisecond interrupt timer so the debounce time is 80 milliseconds. That way all the main has to do is interrogate debounce variable for it's value.

Dave Purola,
N8NTA

[aratti]

if i remove the pauses, there's no debounce, and one push of a button cycles through alot of menus.

I would apply a flag condition to control the key state.

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
ENDIF
.
.
.
.
.
GOTO LOOP

In the above snippet every time you press the key "KEYPRESS" the word variable "Counter" will increment of one unit, no matter how long you keep the key down. If you remove the flag control using pauses, it will be rather complicate to reach the same results.



Al.

[Kamikaze47]

I would apply a flag condition to control the key state.

This would still require some kind of debouncing. The logic state can "bounce" a number of times when pressing a button, so if it toggles back and forth a few times it could still advance the counter more than once for a single key press if the loop is quick enough.

[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?