piezo-knocks problem

Projects General Guidance
1

Hi everyone,

I am new in Arduino. I bought the starter kit and I am trying to do the projects which are in the book of starter kit.

I have problem with piezo. I cannot undesrtand what is going on!!

I am on project 12 (if know the book) . You knock the piezo 3 times and then a servo motor is moving.

Anyway, when I knock on the piezo once, then in the serial monitor I see 2 knocks!!!

#include <Servo.h>

Servo myServo;
const int piezo=A0;
const int switchPin=2;
const int yellowLed=3;
const int greenLed=4;
const int redLed=5;

int knockVal;
int switchVal;

const int quietKnock=10;
const int loudKnock =100;

boolean locked =false;

int nunberOfKnocks =0;


void setup()
{
  myServo.attach(9);
  pinMode(yellowLed,OUTPUT);
  pinMode(redLed,OUTPUT);
  pinMode(greenLed,OUTPUT);
  pinMode(switchPin,INPUT);
  Serial.begin(9600);
        
   digitalWrite(greenLed, HIGH);
   myServo.write(0);
   Serial.println("the box is unlocked");
}

void loop()
{
 
  if (locked == false)
  {
    switchVal=digitalRead(switchPin);
    if (switchVal == HIGH)
    {
      nunberOfKnocks=0;
      locked= true;
      digitalWrite (greenLed, LOW);
      digitalWrite(redLed,HIGH);
      myServo.write(90);
      Serial.println("the box is locked");
      delay(1000);
    }
  }
 
  if (locked ==true)
  {
    knockVal= analogRead(piezo);
   
    if (nunberOfKnocks <3 && knockVal >0)
    {
      if(checkForKnock(knockVal)==true)
      {
        nunberOfKnocks++;
      }
      Serial.print(3-nunberOfKnocks);
      Serial.println("   more knocks to go");
    }
    if (nunberOfKnocks >=3)
    {
      locked=false;
      myServo.write(0);
      delay(20);
      digitalWrite(greenLed, HIGH);
      digitalWrite(redLed, LOW);
      Serial.println("the box is unlocked");
           
    }
  }
}
boolean checkForKnock(int value)
{
  Serial.print("In function: value=");
    Serial.println(value); 
  if (value> quietKnock && value < loudKnock)
  {
    digitalWrite(yellowLed, HIGH);
    delay (50);
    digitalWrite(yellowLed,LOW);
    Serial.print("Valid knock of value");
    Serial.println(value);
    return true;
  }
  else
  {
    Serial.print("Bad kncock value");
    Serial.println (value);
    return false;
  }
}

Can anyone explain me why this happening??? ?

2

Yes, it is a "debounce" problem - the piezo is generating an output for longer than the time the program waits after detecting a "knock".

The more important question is - is it flagging "valid" knocks and will it operate the servo if you knock a number of times?

You could increase the delay in

    digitalWrite(yellowLed, HIGH);
    delay (50);
    digitalWrite(yellowLed,LOW);

to 100.