Hello every body,
I'm a newbee, and i am stoping by an instruction of the code in the project 12 of the starter Kit.
I have received a message from the help mail because i don't understand if the variable "numberOfKnocks" is attaching or not to the function "checkForKnock()". They said not. and i don't understand their message. How the variable "numberOfKnocks" can change if there is not attached to the function " checkForKnock()".

There is the answer of the help desk :

"Integer variable "numberOfKnocks" is not attached to function "checkForKnock()", but actually "numberOfKnocks" is simply increased if "checkForKnock()" returns a TRUE value.

If you can help me I will be gratfull to you.
Best Regards

I'm French and excuse my english.

Can you attach the code? It's difficult to answer without the code.

The code is very simple but i ask to myself :

#include <Servo.h>
// create an instance of the servo library
Servo myServo;

const int piezo = A0; // pin the piezo is attached to
const int switchPin = 2; // pin the switch is attached to
const int yellowLed = 3; // pin the yellow LED is attached to
const int greenLed = 4; // pin the green LED is attached to
const int redLed = 5; // pin the red LED is attached to

// variable for the piezo value
int knockVal;
// variable for the switch value
int switchVal;

// variables for the high and low limits of the knock value
const int quietKnock = 10;
const int loudKnock = 100;

// variable to indicate if locked or not
boolean locked = false;
// how many valid knocks you’ve received
int numberOfKnocks = 0;

void setup() {
// attach the servo to pin 9

// make the LED pins outputs
pinMode(yellowLed, OUTPUT);
pinMode(redLed, OUTPUT);
pinMode(greenLed, OUTPUT);

// set the switch pin as an input
pinMode(switchPin, INPUT);

// start serial communication for debugging

// turn the green LED on
digitalWrite(greenLed, HIGH);

// move the servo to the unlocked position

// print status to the serial monitor
Serial.println(“the box is unlocked!”);

void loop() {

// if the box is unlocked
if (locked == false) {

// read the value of the switch pin
switchVal = digitalRead(switchPin);

// if the button is pressed, lock the box
if (switchVal == HIGH) {
// set the locked variable to “true”
locked = true;

// change the status LEDs
digitalWrite(greenLed, LOW);
digitalWrite(redLed, HIGH);

// move the servo to the locked position

// print out status
Serial.println(“the box is locked!”);

// wait for the servo to move into position

// if the box is locked
if (locked == true) {

// check the value of the piezo
knockVal = analogRead(piezo);

// if there are not enough valid knocks
if (numberOfKnocks < 3 && knockVal > 0) {

// check to see if the knock is in range
if (checkForKnock(knockVal) == true) {

// increment the number of valid knocks

// print status of knocks
Serial.print(3 - numberOfKnocks);
Serial.println(" more knocks to go");

// if there are three knocks
if (numberOfKnocks >= 3) {
// unlock the box
locked = false;

// move the servo to the unlocked position

// wait for it to move

// change status LEDs
digitalWrite(greenLed, HIGH);
digitalWrite(redLed, LOW);
Serial.println(“the box is unlocked!”);

numberOfKnocks = 0;

// this function checks to see if a
// detected knock is within max and min range
boolean checkForKnock(int value) {
// if the value of the knock is greater than
// the minimum, and larger than the maximum
if (value > quietKnock && value < loudKnock) {
// turn the status LED on
digitalWrite(yellowLed, HIGH);
digitalWrite(yellowLed, LOW);
// print out the status
Serial.print("Valid knock of value ");
// return true
return true;
// if the knock is not within range
else {
// print status
Serial.print("Bad knock value ");
// return false
return false;

Thank’s for help !

try to use code tag. So that your code looks like

code here

it's easy to read.

Variables don't get "attached" to anything. If you want a variable to change then you have to have a line of code to execute and change the value.

Right here:

if (checkForKnock(knockVal) == true) {

        // increment the number of valid knocks

It says that if checkForKnock function returns true (there is a knock) then it increments the numberOfKnocks variable by one.

Thank you for help.
it's clear now !