Assignment 5: High(er) voltage and transistors!

/*
  Ultrasonic Distance to LED Brightness

  This code reads distance from an ultrasonic sensor 
  and turns the LED strip on/off depending on how close
  an object or person is to the sensor.
  
  I adapted the code from the Arduino IDE "Fade" example!
*/

// define which Arduino pins are connected to the ultrasonic sensor and  strip (through transistor)
const int trigPin = 11;   // pin that sends out the trigger signal to the ultrasonic sensor
const int echoPin = 12;   // pin that receives the echo signal from the ultrasonic sensor
const int ledPin = 9;     // PWM pin connected to LED strip through transistor

// declare variables for timing, distance, and brightness
long duration;  // stores the time it takes for the sound wave to travel to the object and back
int distance;   // stores the calculated distance (cm
int brightness; // stores the LED brightness value (0 = off, 255 = fully on)

void setup() {
  pinMode(trigPin, OUTPUT);  // set the trigger pin as an output
  pinMode(echoPin, INPUT);   // set the echo pin as an input 
  pinMode(ledPin, OUTPUT);   // set the LED pin as an output so Arduino can control it
  Serial.begin(9600);        // start serial communication for debugging
}

void loop() {
  // Send a short ultrasonic pulse as the first step to measure the distance of an object
  digitalWrite(trigPin, LOW);      // make sure trigger pin is low to start the signal
  delayMicroseconds(2);            // wait for 2 microseconds
  digitalWrite(trigPin, HIGH);     // set trigger pin high to send a sound wave
  delayMicroseconds(10);           // keep it high for 10 microseconds because this is the required pulse length for the ultrasonic sensor
  digitalWrite(trigPin, LOW);      // set trigger pin low again to stop sending the pulse

  // Measure the time it takes for the echo to return 
  // Get the time, in microseconds, that the echo pin stays high
  duration = pulseIn(echoPin, HIGH);

  // Convert the time to distance 
  // sound travels at ~0.034 cm per microsecond, divide by 2 (because it is traveling there and back)
  distance = duration * 0.034 / 2;

  // Limit and map the distance to LED strip brightness 
  distance = constrain(distance, 0, 50);     // limit the measured distance between 0 and 50 cm to avoid extreme values
  brightness = map(distance, 50, 0, 0, 255); // map distance (0 - 50 cm) to brightness (0 - 255), such that 0cm = LEDs off, and 50cm = LEDs fully bright

  // Apply brightness to the LED
  // send PWM signal to LED pin to control the brightness
  analogWrite(ledPin, brightness);

  // Print distance and brightness values to Serial Monitor
  Serial.print("Distance: ");
  Serial.print(distance);           // show measured distance in cm
  Serial.print(" cm  |  Brightness: ");
  Serial.println(brightness);       // show current LED brightness value

  // Adding a short delay before starting the loop again
  delay(100);
}