const int  buttonPin = 3;    // the pin that the pushbutton is attached to
const int led1 = 12;
const int led2 = 11;
const int led3 = 10;
const int led4 = 9;
// the pin that the LED is attached to
// Variables will change:
int PushCounter = 0;   
int buttonState = 0;         // current state of the button
int lastButtonState = 0;     // previous state of the button
void setup() {
 // initialize the button pin as a input:
 pinMode(buttonPin, INPUT);
 // initialize the LED as an output:
 pinMode(led1, OUTPUT);
 pinMode(led2,OUTPUT);
 pinMode(led3,OUTPUT);
 pinMode(led4,OUTPUT);
 // initialize serial communication:
 Serial.begin(9600);
}
void loop() {
 buttonState = digitalRead(buttonPin);
 // compare the buttonState to its previous state
 if (buttonState != lastButtonState) {
   // if the state has changed, increment the counter
   if (buttonState == HIGH) {
     // if the current state is HIGH then the button
     // wend from off to on:
     buttonCounter++;
     Serial.println("on");
     Serial.print("number of button pushes:  ");
     Serial.println(buttonCounter);
   } 
   else {
     // if the current state is LOW then the button
     // wend from on to off:
     Serial.println("off"); 
   }
 }
 // save the current state as the last state, 
 //for next time through the loop
 lastButtonState = buttonState;
 // turns on the LED every four button pushes by 
 // checking the modulo of the button push counter.
 // the modulo function gives you the remainder of 
 // the division of two numbers:
 if (buttonCounter % 2 == 0) {
   digitalWrite(led1, HIGH);
   digitalWrite(led2, HIGH);
   digitalWrite(led3, HIGH);
   digitalWrite(led4, HIGH);
 } else {
  digitalWrite(led1, LOW);
  digitalWrite(led2, LOW);
  digitalWrite(led3, LOW);
  digitalWrite(led4, LOW);
 }
}

EXPANDED TECHNICAL DETAILS

Tactile Pulse Detection Interaction

This project explores the use of a simple "Tap" or knock sensor to create a touchless, vibration-based interface for home appliances.

• Piezoelectric Vibration Sensing: Uses a Piezo element as an analog input. When the surface is tapped, the Piezo generates a small voltage spike ($V_{out}$). The Arduino samples this using its ADC and applies a "Signal Threshold" to filter out background noise.
• Toggle State Machine: A single tap is programmed to flip a software "State." This state then drives a 5V Relay, allowing the user to turn a desk lamp or a fan on/off just by knocking on the table.

Sensitivity Calibration

• Automatic Baseline Nulling: Includes a "Self-Calibration" routine on startup; the Arduino samples the room's ambient vibration level (e.g., from a nearby PC fan) and sets the trigger threshold just above it.