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Arduino Forum Why does my Arduino switch Debounce routine bounce?
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Related

Why does my Arduino switch Debounce routine bounce?

colporteur
colporteur over 2 years ago

Why does the LED flash twice with one push and release of the button?

#include <Servo.h>

Servo Stop_servo;  // create servo object to control a servo

// Buttons with Pull-Ups are "backwards"
// Some DEFINEs to make reading code easier
#define PUSHED false
#define NOT_PUSHED true
#define WATCH_BUTTON true
#define IGNORE_BUTTON false

// Time to wait for bounce, in MICROsconds
const int buttonWaitInterval = 6000;
// Pins for LED and Button
const int LEDpin = 5;
const int BUTTONpin = 2;
float Minpos = 0;    // variable to store the servo position
float Maxpos = 255;  //greatest travel of servo

// Used to track how long between "bounces"
unsigned long previousMicros = 0;

// Used to track state of button (high or low)
boolean previousButtonState = NOT_PUSHED;

// Variable reporting de-bounced state.
boolean debouncedButtonState = NOT_PUSHED;

// Tracks if we are waiting for a "bounce" event
boolean bounceState = false;

// Nothing surprising here
void setup() {
  pinMode(LEDpin, OUTPUT);
  pinMode(BUTTONpin, INPUT_PULLUP);
  digitalWrite(LEDpin, LOW);
  Stop_servo.attach(3);  // attaches the servo on pin 3 to the servo object
  Stop_servo.write(0);

  Serial.begin(9600);
  Serial.println(F("Serial Initialized"));
}

void loop() {

  // This needs to be called periodically to
  // update the timers and button status
  updateButton();
  // This replaces: digitalRead(BUTTONpin);
  //digitalWrite(LEDpin, debouncedButtonState);
  if (debouncedButtonState == LOW) {
    digitalWrite(LEDpin, HIGH);
    delay(500);
    digitalWrite(LEDpin, LOW);
    delay(500);
    Stop_servo.write(255);
    delay(5000);
    Stop_servo.write(0);
    Serial.println(F("servo cycled"));
  }
}

// All of the magic happens here
void updateButton() {
  // We are waiting for any activity on the button
  if (bounceState == WATCH_BUTTON) {
    // Get and store current button state
    boolean currentButtonState = digitalRead(BUTTONpin);
    // Check to see if a transition has occured (and only one)
    if (previousButtonState != currentButtonState) {
      // A transition was detected, ignore the others for a while
      bounceState = IGNORE_BUTTON;
      // Store current time (start the clock)
      previousMicros = micros();
    }
    // Keep storing existing button state, if we're watching
    previousButtonState = currentButtonState;
  }
  // We are waiting for the buttonWaitInterval to elapse
  if (bounceState == IGNORE_BUTTON) {
    // Compare current value of micros to previously stored, enough time yet?
    unsigned long currentMicros = micros();
    if ((unsigned long)(currentMicros - previousMicros) >= buttonWaitInterval) {
      // Store the state of the button/pin to debouncedButtonState, which "reports"
      // the correct value. This allows for the code to handle active high or low inputs
      debouncedButtonState = digitalRead(BUTTONpin);
      // Go back to watching the button again.
      bounceState = WATCH_BUTTON;
    }
  }
}

I'm trying to use Baldengineer debounce code to read a button and take an action. Each press of the button causes the LED to flash twice. The serial output reflects the routine running twice. 

I have failed in my code changes to get the result I hope. I have looked at Internet and have found no hints to help.

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Top Replies

  • scottiebabe
    scottiebabe over 2 years ago in reply to scottiebabe +4
    Technical forums are great, so many great tidbits of knowledge shared in this thread! One more demonstration showing why a schmitt trigger is an important part of the solution. I wrote a simple PIO…
  • dougw
    dougw over 2 years ago +3
    Debouncing may be good practice, but it would seem you don't need it here. If you start your LED and servo cycle as soon as a button push is first detected, all button bouncing will be long over before…
  • shabaz
    shabaz over 2 years ago +3
    Hi Sean, I've not looked in detail, but it seems that you wish to move a servo just once, if a button is pressed. Your delay() functions are actually already performing a button-pushed-down debounce…
Parents
  • shabaz
    shabaz over 2 years ago

    Hi Sean,


    I've not looked in detail, but it seems that you wish to move a servo just once, if a button is pressed. Your delay() functions are actually already performing a button-pushed-down debounce.
    That's because no mechanical switch will have bouncing output for longer than (say) 50 msec (this is an arbitrary value), and your delay() functions are clearly longer than that. So the debounce is effectively redundant, it's already achieved by your delay being longer.

    However there could be a scenario where the user simply holds down the button for many seconds. I think you wish to hold off until the button is released, before performing any more servo movements?

    If so, what you could do is simply check if the button is being held down after the servo has completed its motion, and you can just hold off there until the button is released, and have a little delay at the end too. It will be pretty rock-solid.

    Here's what it would look like approximately in pseudocode:


    IF the button is pressed:
        LED on
        MOVE servo
        WAIT 5 seconds
        LED off
        IF the button is still pressed: // User is holding it down for longer than 5 seconds!
            WAIT until button is released
            WAIT 100 msec // i.e. wait longer than 50 msec to be sure the button is not bouncing
    LOOP again

    Here is what it could look like in code:


    void loop() {
        // check if the button is pressed
        if (digitalRead(BUTTONpin) == LOW) {
            // turn LED on
            digitalWrite(LEDpin, HIGH);
            // move the servo and then wait 5 seconds
            Stop_servo.write(255);
            delay(5000);
            // move the servo back
            Stop_servo.write(0);
            // turn LED off
            digitalWrite(LEDpin, LOW);
            // if the user is holding down the button, wait for it to be released
            wait_for_button_release();
        }
    }

    That function wait_for_button_release() would be something like:

    void wait_for_button_release(void) {
        // Is the user holding down the button?
        if (digitalRead(BUTTONpin) == LOW) {
            // wait for the button to be released, by just repeatedly checking if the button is still pressed:
            while (digitalRead(BUTTONpin) == LOW) {
                delay(10); // tiny delay
            }
            // ok the user has released the button. Perform the debounce by waiting 100 msec which is greater than our arbitrary 50 msec assumption
            delay(100);
        }
    }

    The editor toolbar seems broken, so I had to just put the code in bold, instead of with proper formatting.

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  • shabaz
    shabaz over 2 years ago

    Hi Sean,


    I've not looked in detail, but it seems that you wish to move a servo just once, if a button is pressed. Your delay() functions are actually already performing a button-pushed-down debounce.
    That's because no mechanical switch will have bouncing output for longer than (say) 50 msec (this is an arbitrary value), and your delay() functions are clearly longer than that. So the debounce is effectively redundant, it's already achieved by your delay being longer.

    However there could be a scenario where the user simply holds down the button for many seconds. I think you wish to hold off until the button is released, before performing any more servo movements?

    If so, what you could do is simply check if the button is being held down after the servo has completed its motion, and you can just hold off there until the button is released, and have a little delay at the end too. It will be pretty rock-solid.

    Here's what it would look like approximately in pseudocode:


    IF the button is pressed:
        LED on
        MOVE servo
        WAIT 5 seconds
        LED off
        IF the button is still pressed: // User is holding it down for longer than 5 seconds!
            WAIT until button is released
            WAIT 100 msec // i.e. wait longer than 50 msec to be sure the button is not bouncing
    LOOP again

    Here is what it could look like in code:


    void loop() {
        // check if the button is pressed
        if (digitalRead(BUTTONpin) == LOW) {
            // turn LED on
            digitalWrite(LEDpin, HIGH);
            // move the servo and then wait 5 seconds
            Stop_servo.write(255);
            delay(5000);
            // move the servo back
            Stop_servo.write(0);
            // turn LED off
            digitalWrite(LEDpin, LOW);
            // if the user is holding down the button, wait for it to be released
            wait_for_button_release();
        }
    }

    That function wait_for_button_release() would be something like:

    void wait_for_button_release(void) {
        // Is the user holding down the button?
        if (digitalRead(BUTTONpin) == LOW) {
            // wait for the button to be released, by just repeatedly checking if the button is still pressed:
            while (digitalRead(BUTTONpin) == LOW) {
                delay(10); // tiny delay
            }
            // ok the user has released the button. Perform the debounce by waiting 100 msec which is greater than our arbitrary 50 msec assumption
            delay(100);
        }
    }

    The editor toolbar seems broken, so I had to just put the code in bold, instead of with proper formatting.

    • Cancel
    • Vote Up +3 Vote Down
    • Sign in to reply
    • Cancel
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