Debouncing Multiple Switches

Debouncing Multiple Switches

源自於　http://www.ediy.com.my/index.php/tutorials/item/96-debouncing-multiple-switches

If you want to input a manual switch signal into a digital circuit you'll need to debounce the signal so a single press doesn't appear like multiple presses. 

There is a Bounce library for Arduino which is very easy to use. However there is limitations with this Boounce library.

• You are unlikely to enable the internal pull-up resistor on switch pins, therefore each switch require an external pull-up resistor
• It is not possible to detect the switch state before main loop (setup). When you press a switch during power on, you will never get the state of the switch.

Adafruit wrote an example code for multi-button checker with debouncing which will solve that two problems.

#define DEBOUNCE 10  // button debouncer, how many ms to debounce, 5+ ms is usually plenty





// here is where we define the buttons that we'll use. button "1" is the first, button "6" is the 6th, etc


byte buttons[] = {4, 5, 6, 7, 8, 9}; 





// This handy macro lets us determine how big the array up above is, by checking the size


#define NUMBUTTONS sizeof(buttons)





// we will track if a button is just pressed, just released, or 'currently pressed' 


byte pressed[NUMBUTTONS], justpressed[NUMBUTTONS], justreleased[NUMBUTTONS];





void setup() {


byte i;





// set up serial port


Serial.begin(9600);


Serial.print("Button checker with ");


Serial.print(NUMBUTTONS, DEC);


Serial.println(" buttons");


// pin13 LED


pinMode(13, OUTPUT);





// Make input & enable pull-up resistors on switch pins


for (i=0; i< NUMBUTTONS; i++) {


pinMode(buttons[i], INPUT);


digitalWrite(buttons[i], HIGH);


}


}





void check_switches()


{


static byte previousstate[NUMBUTTONS];


static byte currentstate[NUMBUTTONS];


static long lasttime;


byte index;


if (millis() < lasttime) {


lasttime = millis(); // we wrapped around, lets just try again


}




if ((lasttime + DEBOUNCE) > millis()) {


return; // not enough time has passed to debounce


}


// ok we have waited DEBOUNCE milliseconds, lets reset the timer


lasttime = millis();





for (index = 0; index < NUMBUTTONS; index++) {


justpressed[index] = 0;       // when we start, we clear out the "just" indicators


justreleased[index] = 0;





currentstate[index] = digitalRead(buttons[index]);   // read the button


if (currentstate[index] == previousstate[index]) {


if ((pressed[index] == LOW) &amp;&amp; (currentstate[index] == LOW)) {


// just pressed


justpressed[index] = 1;


}


else if ((pressed[index] == HIGH) &amp;&amp; (currentstate[index] == HIGH)) {


// just released


justreleased[index] = 1;


}


pressed[index] = !currentstate[index];  // remember, digital HIGH means NOT pressed


}


//Serial.println(pressed[index], DEC);


previousstate[index] = currentstate[index];   // keep a running tally of the buttons


}


}





void loop() {


check_switches();      // when we check the switches we'll get the current state





for (byte i = 0; i < NUMBUTTONS; i++) {


if (justpressed[i]) {


Serial.print(i, DEC);


Serial.println(" Just pressed"); 


// remember, check_switches() will CLEAR the 'just pressed' flag


}


if (justreleased[i]) {


Serial.print(i, DEC);


Serial.println(" Just released");


// remember, check_switches() will CLEAR the 'just pressed' flag


}


if (pressed[i]) {


Serial.print(i, DEC);


Serial.println(" pressed");


// is the button pressed down at this moment


}


}


}

I'm modifying the example code, it is useful if you want something to only happen once when a button is pressed.

#define DEBOUNCE 10  // how many ms to debounce, 5+ ms is usually plenty





//define the buttons that we'll use.


byte buttons[] = {4, 5, 6, 7, 8, 9}; 





//determine how big the array up above is, by checking the size


#define NUMBUTTONS sizeof(buttons)





//track if a button is just pressed, just released, or 'currently pressed' 


byte pressed[NUMBUTTONS], justpressed[NUMBUTTONS], justreleased[NUMBUTTONS];


byte previous_keystate[NUMBUTTONS], current_keystate[NUMBUTTONS];





void setup() {


byte i;


Serial.begin(9600); //set up serial port


Serial.print("Button checker with ");


Serial.print(NUMBUTTONS, DEC);


Serial.println(" buttons");


// Make input & enable pull-up resistors on switch pins


for (i=0; i< NUMBUTTONS; i++) {


pinMode(buttons[i], INPUT);


digitalWrite(buttons[i], HIGH);


}


}





void loop() {


byte thisSwitch=thisSwitch_justPressed();


switch(thisSwitch)


{  


case 0: 


Serial.println("switch 1 just pressed"); break;


case 1: 


Serial.println("switch 2 just pressed"); break;


case 2: 


Serial.println("switch 3 just pressed"); break;


case 3: 


Serial.println("switch 4 just pressed"); break;


case 4: 


Serial.println("switch 5 just pressed"); break;


case 5: 


Serial.println("switch 6 just pressed"); break;    


}


}





void check_switches()


{


static byte previousstate[NUMBUTTONS];


static byte currentstate[NUMBUTTONS];


static long lasttime;


byte index;


if (millis() < lasttime) {


// we wrapped around, lets just try again


lasttime = millis();


}


if ((lasttime + DEBOUNCE) > millis()) {


// not enough time has passed to debounce


return; 


}


// ok we have waited DEBOUNCE milliseconds, lets reset the timer


lasttime = millis();


for (index = 0; index < NUMBUTTONS; index++) {


justpressed[index] = 0;       //when we start, we clear out the "just" indicators


justreleased[index] = 0;


currentstate[index] = digitalRead(buttons[index]);   //read the button


if (currentstate[index] == previousstate[index]) {


if ((pressed[index] == LOW) &amp;&amp; (currentstate[index] == LOW)) {


// just pressed


justpressed[index] = 1;


}


else if ((pressed[index] == HIGH) &amp;&amp; (currentstate[index] == HIGH)) {


justreleased[index] = 1; // just released


}


pressed[index] = !currentstate[index];  //remember, digital HIGH means NOT pressed


}


previousstate[index] = currentstate[index]; //keep a running tally of the buttons


}


}





byte thisSwitch_justPressed() {


byte thisSwitch = 255;


check_switches();  //check the switches &amp; get the current state


for (byte i = 0; i < NUMBUTTONS; i++) {


current_keystate[i]=justpressed[i];


if (current_keystate[i] != previous_keystate[i]) {


if (current_keystate[i]) thisSwitch=i;


}


previous_keystate[i]=current_keystate[i];


}  


return thisSwitch;


}