Experiment 2: LED and buzzer with digital, PWM and ultrasonic control

1int ledPin = 2;2int buzzPin = 4;3 4void setup() {5    // put your setup code here, to run once:6    Serial.begin(9600);7    Serial.println("Hello Ardino!!");8 9    pinMode(ledPin, OUTPUT);10    pinMode(buzzPin, OUTPUT);11}12 13void loop() {14    // put your main code here, to run repeatedly:15    digitalWrite(ledPin, HIGH);16    digitalWrite(buzzPin, HIGH);17    delay(1000);18 19    digitalWrite(ledPin, LOW);20    digitalWrite(buzzPin, LOW);21    delay(1000);22}

1. Lines 1 to 2
   Two outputs.
2. Lines 6 to 7
   Banner on start. The typo is inside a string literal and has no effect.
3. Lines 9 to 10
   Both pins driven.
4. Lines 15 to 17
   Both HIGH, hold 1 s. The active buzzer’s oscillator runs while powered.
5. Lines 19 to 21
   Both LOW, hold 1 s. Period 2 s, 0.5 Hz.

1int ledPin = 7;2int buzzPin = 9;3int potPin = A7;4int readVal;5int mapVal;6 7void setup() {8    // put your setup code here, to run once:9    Serial.begin(9600);10    Serial.print("HEllo");11 12    pinMode(buzzPin, OUTPUT);13    pinMode(potPin, INPUT);14}15 16void loop() {17    // put your main code here, to run repeatedly:18    readVal = analogRead(potPin);19    Serial.println(readVal);20 21    mapVal = map(readVal, 0, 1023, 0, 255);22    Serial.println(mapVal);23 24    analogWrite(ledPin, mapVal);25    analogWrite(buzzPin, mapVal);26}

1. Lines 1 to 3
   PWM pins 7 and 9; analog input A7 (MEGA only).
2. Lines 4 to 5
   Raw and scaled values, global so they persist (they would work as locals too).
3. Line 10
   print without a newline, so the first reading is glued onto it (“HEllo163”).
4. Lines 12 to 13
   No pinMode for ledPin: analogWrite() sets output mode itself. INPUT on the analog pin is redundant but harmless.
5. Lines 18 to 19
   One ADC conversion (about 0.1 ms on AVR), printed.
6. Lines 21 to 22
   Integer rescale, printed. The monitor therefore alternates raw and mapped values.
7. Lines 24 to 25
   Load the same duty into both PWM channels. No delay: the loop rate is limited by how fast Serial.println can push bytes at 9600 baud.

1int ledPin = 12;2int trigPin = 3;3int echoPin = A7;4int buzzPin = 7;5int duration;6int distance;7 8void setup() {9    // put your setup code here, to run once:10    Serial.begin(9600);11    Serial.println("Hello");12 13    pinMode(trigPin, OUTPUT);14    pinMode(echoPin, INPUT);15    pinMode(ledPin, OUTPUT);16}17 18void loop() {19    // put your main code here, to run repeatedly:20    digitalWrite(trigPin, LOW);21    delayMicroseconds(2);22    digitalWrite(trigPin, HIGH);23    delayMicroseconds(10);24    digitalWrite(trigPin, LOW);25    delayMicroseconds(2);26 27    duration = pulseIn(echoPin, HIGH);28 29    distance = duration / 2 * 0.0343;30    Serial.println(distance);31 32    if (distance <= 200) {33        digitalWrite(ledPin, HIGH);34        digitalWrite(buzzPin, HIGH);35        delay(1000);36    }37    else {38        digitalWrite(ledPin, LOW);39        digitalWrite(buzzPin, LOW);40        delay(1000);41    }42}

1. Lines 1 to 4
   Pin map: two outputs, the trigger output, and the echo input.
2. Lines 5 to 6
   16-bit int on AVR: −32768 to 32767. Relevant to the overflow limit below.
3. Lines 13 to 15
   TRIG out, ECHO in, LED out. buzzPin is never set to OUTPUT; see Limits.
4. Lines 20 to 21
   Ensure a clean LOW so the next edge is a proper rising edge.
5. Lines 22 to 23
   The 10 µs trigger pulse the datasheet requires.
6. Line 27
   Blocks until ECHO rises, then times how long it stays HIGH, in µs. Returns 0 if nothing arrives within the default 1 s timeout.
7. Line 29
   Integer division first, then a float multiply, then truncation into int. 10620 µs → 5310 → 182.13 → 182 cm.
8. Line 30
   Report every reading.
9. Lines 32 to 35
   Within 200 cm: both outputs HIGH, wait 1 s.
10. Lines 37 to 39
    Otherwise both LOW, wait 1 s. So the system samples at about 1 Hz.