The document discusses piezo buzzers, which are electronic devices that produce sound. It explains that piezo buzzers use piezoelectric materials, which generate electricity when pressure is applied. Common piezoelectric materials include piezoceramics, which change shape with alternating electric fields to produce sound. The document also provides code examples to control a piezo buzzer from an Arduino and detect knocks with a sensor.

1. BUZZER

2. • Piezo buzzer is an electronic device commonly used to
produce sound.
• Light weight, simple construction and low price make
it usable in various applications like car/truck reversing
indicator, computers, call bells etc.
• Piezo buzzer is based on the inverse principle of piezo
electricity . It is the phenomena of generating
electricity when mechanical pressure is applied to
certain materials and the vice versa is also true. Such
materials are called piezo electric materials.
• Piezo electric materials are either naturally available or
manmade. Piezoceramic is class of manmade material,
which poses piezo electric effect and is widely used to
make disc, the heart of piezo buzzer. When subjected
to an alternating electric field they stretch or
compress, in accordance with the frequency of the
signal thereby producing sound.

4. CODE
const int buzzer = 9; //buzzer to arduino pin 9
void setup()
{
pinMode(buzzer, OUTPUT); // initializing pin 9 as an output
}
void loop()
{
digitalWrite(buzzer, HIGH); // (HIGH )
delay(1000); // wait for a second
digitalWrite(buzzer, LOW); // LOW
delay(1000); // wait for a second
}

5. int ledPin = 13;
int knockSensor = A0;
byte val = 0;
int statePin = LOW;
int THRESHOLD = 70;
void setup() {
pinMode(ledPin, OUTPUT);
Serial.begin(9600);
}
void loop() {
val = analogRead(knockSensor);
if (val >= THRESHOLD) {
statePin = !statePin;
digitalWrite(ledPin, statePin);
Serial.println("Knock!");
}
delay(100); // we have to make a delay to avoid overloading
}
KNOCK