Day 297, Adding a Push Button to the STM32 and debouncing it with Software

I am reading this book DIY Microcontroller Projects for Hobbyists, and I spent some time on the chapter 3 where it talks about an exercise to Turn On and Off a led using a Push button:

The board and everything already connected look like this:

And when the push button is clicked, the led (on the left) is turned on (it looks like it’s not but it’s ON):

The connection of circuit was pretty straightforward, I was just connecting:

  1. one pin of the push button to Ground in the blue pill
  2. the other pin to port B0 (One of the digital ports) in (pin mode INPUT_PULLUP)
  3. then port B12 to a resistor then to the positive pin of the Led (pin mode OUTPUT)
  4. and then negative pin of the led to Ground

Then just loading the peace of software in the link below (compiling it on the Arduino app and uploading it to the blue pill):

I did some adjustments to the original code because I didn’t like the fact that it is polluting the loop() method with a lot of unnecessary code so I created a class and added everything in there, I just returned the value that I am interested in which is the final status (after debouncing) of the push button, which is LOW or HIGH (or Off and ON)

so I wanted the loop code to look simple, like this:

void loop() {
  int led_status = button_handler.read_status();
  
  // set the LED:
  digitalWrite(PinLED, led_status);
}

And here the full code:

https://github.com/PacktPublishing/DIY-Microcontroller-Projects-for-Hobbyists/pull/2

/* 
 * Program that turns an LED on when its user presses a push button.
 * It debouonces the push button via software.
 * Miguel Garcia-Ruiz. 
 * The code is based on this web page: https://www.arduino.cc/en/Tutorial/BuiltInExamples/Debounce
 * Version: 1.0
 * Date: October 19, 2020
 
 
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
 * THE SOFTWARE.
 
 
*/
#define PinLED PB12
#define PinPushButton PB0

class PushButtonHelper {
  public: 
    PushButtonHelper(int PinPushBtn) {
      PIN_PUSH_BUTTON = PinPushBtn;
    }

    int read_status() {
      current_reading = digitalRead(PIN_PUSH_BUTTON);
      // check to see if you just pressed the button
      // (i.e. the input went from LOW to HIGH), and you've waited long enough
      // since the last press to ignore any noise:

      // If the switch changed, due to noise or pressing:
      // reset the debouncing timer
      reset_debouncing_timer();

      // whatever the reading is at, it's been there for longer than the debounce
      // delay, so take it as the actual current state:
      if (isTimeElapsedLessThanOurDefaultDelayTime() && pushButtonStateChanged()) {
        // if the button state has changed:
        button_state = current_reading;

        // only toggle the Value/LED if the new button state is HIGH
        if (isButtonActivelyPressed()) {
          status = !status;
        } 
      }

      // save the reading. Next time through the loop, it'll be the lastButtonState:
      last_button_state = current_reading;
      return status;
    }

  private: 
    int PIN_PUSH_BUTTON;                    // port to read from
    unsigned long last_debouncing_time = 0; // the last time the output pin was toggled
    unsigned long debouncing_delay = 50;    // the debounce time; increase if the output flickers
    int status = HIGH;                      // the current state of the output pin
    int button_state;                       // the current reading from the input pin
    int last_button_state = LOW;            // the previous reading from the input pin
    int current_reading;

    void reset_debouncing_timer() {
      if(current_reading != last_button_state) {
        last_debouncing_time = millis();
      }
    }

    int isTimeElapsedLessThanOurDefaultDelayTime() {
      return (millis() - last_debouncing_time) > debouncing_delay;
    }

    int pushButtonStateChanged() {
      return current_reading != button_state;
    }

    int isButtonActivelyPressed() {
      return button_state == HIGH;
    }
} button_handler(PinPushButton);

void setup() {
  pinMode(PinLED, OUTPUT);
  pinMode(PinPushButton, INPUT_PULLUP);
}

void loop() {
  int led_status = button_handler.read_status();
  
  // set the LED:
  digitalWrite(PinLED, led_status);
}

Published by Victor De la Rocha

Colima, Mx

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