Parking assist: beep before you bump

Story 1: See the distancemeasure, print

#include <HCSR04.h>

const int triggerPin = 12;
const int echoPin = 11;
UltraSonicDistanceSensor sensor(triggerPin, echoPin);

void setup() {
  Serial.begin(9600);                 // talk to the computer: open the Serial Monitor at 9600
}

void loop() {
  float distance = sensor.measureDistanceCm();   // -1 when nothing is in range
  Serial.print(distance);
  Serial.println(" cm");
  delay(200);
}

const int sensorPin = A0;           // US-016 OUT; RANGE on 5V: the 3 m range

float measureDistance() {            // the US-016 gives a voltage: on the 3 m range one step is 3 mm
  return analogRead(sensorPin) * 0.3;    // cm
}

void setup() {
  Serial.begin(9600);                 // talk to the computer: open the Serial Monitor at 9600
}

void loop() {
  float distance = measureDistance();   // always a number, in cm
  Serial.print(distance);
  Serial.println(" cm");
  delay(200);
}

Open the Serial Monitor (the magnifying glass, top right) and set it to 9600. Hold your hand in front of the sensor and move it: the numbers follow your hand. float is a number with a decimal point.

Check the US-016 with a tape measure: hold a book at 20, 50 and 100 cm. If the numbers are off by the same factor, change the 300 in measureDistance: that is calibrating a sensor.

Your turn: how close can your hand come before the numbers go strange? And how far away does the wall still count?

Story 2: Red when too closea rule with if

#include <HCSR04.h>

const int triggerPin = 12;
const int echoPin = 11;
const int redLedPin = 2;
const int greenLedPin = 4;
const int tooClose = 30;            // cm
UltraSonicDistanceSensor sensor(triggerPin, echoPin);

void setup() {
  Serial.begin(9600);
  pinMode(redLedPin, OUTPUT);
  pinMode(greenLedPin, OUTPUT);
}

void loop() {
  float distance = sensor.measureDistanceCm();
  Serial.println(distance);
  if (distance > 0 && distance < tooClose) {     // -1 means: nothing in range, so that counts as far
    digitalWrite(redLedPin, HIGH);
    digitalWrite(greenLedPin, LOW);
  } else {
    digitalWrite(redLedPin, LOW);
    digitalWrite(greenLedPin, HIGH);
  }
  delay(100);
}

const int sensorPin = A0;           // US-016 OUT; RANGE on 5V: the 3 m range
const int redLedPin = 2;
const int greenLedPin = 4;
const int tooClose = 30;            // cm

float measureDistance() {            // the US-016 gives a voltage: on the 3 m range one step is 3 mm
  return analogRead(sensorPin) * 0.3;    // cm
}

void setup() {
  Serial.begin(9600);
  pinMode(redLedPin, OUTPUT);
  pinMode(greenLedPin, OUTPUT);
}

void loop() {
  float distance = measureDistance();
  Serial.println(distance);
  if (distance > 0 && distance < tooClose) {     // the US-016 never gives -1; the check does no harm
    digitalWrite(redLedPin, HIGH);
    digitalWrite(greenLedPin, LOW);
  } else {
    digitalWrite(redLedPin, LOW);
    digitalWrite(greenLedPin, HIGH);
  }
  delay(100);
}

The sensor measures, the if decides, the LEDs show it. && means and: both must be true. The first part keeps −1 out, because −1 is smaller than 30 and would look like "very close".The US-016 never gives −1; the first part keeps the program the same for both sensors.

Your turn: change tooClose until the red comes on exactly where you want it.

Story 3: Beep faster, closertone, map

#include <HCSR04.h>

const int triggerPin = 12;
const int echoPin = 11;
const int redLedPin = 2;
const int greenLedPin = 4;
const int buzzerPin = 8;
const int tooClose = 30;            // cm: from here the beeping starts
UltraSonicDistanceSensor sensor(triggerPin, echoPin);

void setup() {
  pinMode(redLedPin, OUTPUT);
  pinMode(greenLedPin, OUTPUT);
  pinMode(buzzerPin, OUTPUT);
}

void loop() {
  float distance = sensor.measureDistanceCm();
  if (distance > 0 && distance < tooClose) {
    digitalWrite(redLedPin, HIGH);
    digitalWrite(greenLedPin, LOW);
    int gap = map((int) distance, 0, tooClose, 50, 500);   // closer: a shorter gap between the beeps
    tone(buzzerPin, 1000);          // a beep of 1000 Hz ...
    delay(60);
    noTone(buzzerPin);              // ... for 60 ms
    delay(gap);
  } else {
    digitalWrite(redLedPin, LOW);
    digitalWrite(greenLedPin, HIGH);
    delay(100);
  }
}

const int sensorPin = A0;           // US-016 OUT; RANGE on 5V: the 3 m range
const int redLedPin = 2;
const int greenLedPin = 4;
const int buzzerPin = 8;
const int tooClose = 30;            // cm: from here the beeping starts

float measureDistance() {            // the US-016 gives a voltage: on the 3 m range one step is 3 mm
  return analogRead(sensorPin) * 0.3;    // cm
}

void setup() {
  pinMode(redLedPin, OUTPUT);
  pinMode(greenLedPin, OUTPUT);
  pinMode(buzzerPin, OUTPUT);
}

void loop() {
  float distance = measureDistance();
  if (distance > 0 && distance < tooClose) {
    digitalWrite(redLedPin, HIGH);
    digitalWrite(greenLedPin, LOW);
    int gap = map((int) distance, 0, tooClose, 50, 500);   // closer: a shorter gap between the beeps
    tone(buzzerPin, 1000);          // a beep of 1000 Hz ...
    delay(60);
    noTone(buzzerPin);              // ... for 60 ms
    delay(gap);
  } else {
    digitalWrite(redLedPin, LOW);
    digitalWrite(greenLedPin, HIGH);
    delay(100);
  }
}

A beep is a short tone and a gap. map turns the distance into the gap: 30 cm gives 500 ms between beeps, 0 cm gives 50 ms. The closer, the faster, just like in a real car.

Your turn: make the note higher when it is closer too: a second map for the number in tone.

Story 4: Park like a real carzones with else if

#include <HCSR04.h>

const int triggerPin = 12;
const int echoPin = 11;
const int redLedPin = 2;
const int yellowLedPin = 3;
const int greenLedPin = 4;
const int buzzerPin = 8;
const int slowDown = 40;            // cm: yellow
const int tooClose = 20;            // cm: red and beeping
const int stopHere = 8;             // cm: red and a steady tone
UltraSonicDistanceSensor sensor(triggerPin, echoPin);

void setup() {
  pinMode(redLedPin, OUTPUT);
  pinMode(yellowLedPin, OUTPUT);
  pinMode(greenLedPin, OUTPUT);
  pinMode(buzzerPin, OUTPUT);
}

void lights(bool red, bool yellow, bool green) {
  digitalWrite(redLedPin, red);
  digitalWrite(yellowLedPin, yellow);
  digitalWrite(greenLedPin, green);
}

void loop() {
  float distance = sensor.measureDistanceCm();
  if (distance < 0 || distance >= slowDown) {    // far away, or nothing in range
    lights(false, false, true);
    noTone(buzzerPin);
    delay(100);
  } else if (distance >= tooClose) {             // getting close: slow down
    lights(false, true, false);
    noTone(buzzerPin);
    delay(100);
  } else if (distance >= stopHere) {             // close: beep, faster and faster
    lights(true, false, false);
    int gap = map((int) distance, stopHere, tooClose, 60, 400);
    tone(buzzerPin, 1000);
    delay(60);
    noTone(buzzerPin);
    delay(gap);
  } else {                                       // stop!
    lights(true, false, false);
    tone(buzzerPin, 1500);
    delay(100);
  }
}

const int sensorPin = A0;           // US-016 OUT; RANGE on 5V: the 3 m range
const int redLedPin = 2;
const int yellowLedPin = 3;
const int greenLedPin = 4;
const int buzzerPin = 8;
const int slowDown = 40;            // cm: yellow
const int tooClose = 20;            // cm: red and beeping
const int stopHere = 8;             // cm: red and a steady tone

float measureDistance() {            // the US-016 gives a voltage: on the 3 m range one step is 3 mm
  return analogRead(sensorPin) * 0.3;    // cm
}

void setup() {
  pinMode(redLedPin, OUTPUT);
  pinMode(yellowLedPin, OUTPUT);
  pinMode(greenLedPin, OUTPUT);
  pinMode(buzzerPin, OUTPUT);
}

void lights(bool red, bool yellow, bool green) {
  digitalWrite(redLedPin, red);
  digitalWrite(yellowLedPin, yellow);
  digitalWrite(greenLedPin, green);
}

void loop() {
  float distance = measureDistance();
  if (distance < 0 || distance >= slowDown) {    // far away, or nothing in range
    lights(false, false, true);
    noTone(buzzerPin);
    delay(100);
  } else if (distance >= tooClose) {             // getting close: slow down
    lights(false, true, false);
    noTone(buzzerPin);
    delay(100);
  } else if (distance >= stopHere) {             // close: beep, faster and faster
    lights(true, false, false);
    int gap = map((int) distance, stopHere, tooClose, 60, 400);
    tone(buzzerPin, 1000);
    delay(60);
    noTone(buzzerPin);
    delay(gap);
  } else {                                       // stop!
    lights(true, false, false);
    tone(buzzerPin, 1500);
    delay(100);
  }
}

Four zones, one after the other: else if only runs when everything above it was false, so the checks can go from far to near. || means or. The function lights sets all three LEDs in one line.

Your turn: park a toy car. Which numbers for the zones feel right for a real garage?