Published February 5, 2020 © MIT

Distance Sensor

Mount in front of your garage to help you park at teh exact right distance.

IntermediateFull instructions provided2 hours10,200

Things used in this project

Hardware components

Pushbutton Switch, Momentary

The enclosure has an opening for a 16mm button.

Resistor 10k ohm

Ultrasonic Sensor - HC-SR04 (Generic)

Adafruit NeoPixel Digital RGBW LED Strip - White PCB 30 LED/m

I used a strip containing 8 NeoPixels, but you can adapt the code to use more or fewer.

Arduino Mega 2560

The wiring diagram uses an Arduino Mega, but this would just as easily run an on Uno. It would probably also run on other boards, but I haven't tested it.

GE Outlet Light Socket

(Optional)

Hand tools and fabrication machines

3D Printer (generic)

Used for printing the enclosure. Optional if you can find a way to secure all the components.

Story

I kept hitting the back of my garage so instead of learning how to drive, I made a gadget.

This senses distance from a vehicle and lights up to show how close. Once you reach the desired distance, it flashes red.

How do you set the distance you ask? There is a handy push-button. Whenever the button is pressed, the device permanently saves the distance.

To power the device, I used the light socket adapter to attach it to my garage door opener. That way, whenever the garage light is on, the sensor is working.

Here's a video of the sensor in action:

Schematics

Code

Distance Senor Code

#include <Adafruit_NeoPixel.h>
#ifdef __AVR__
#include <avr/power.h>
#endif
#include <EEPROM.h>

#define PIN 12
#define BUTTON_PIN 11
#define echoPin 10
#define trigPin 9
#define max_dist 300
#define set_loc 1
#define NUM_LEDS 9
#define BRIGHTNESS 50

Adafruit_NeoPixel strip = Adafruit_NeoPixel(NUM_LEDS, PIN, NEO_GRBW + NEO_KHZ800);


//Initialize glabal variables
int set_dist;
float duration, distance;

void setup() {
  // Initialize neopixels
  // This is for Trinket 5V 16MHz, you can remove these three lines if you are not using a Trinket
#if defined (__AVR_ATtiny85__)
  if (F_CPU == 16000000) clock_prescale_set(clock_div_1);
#endif
  // End of trinket special code

  strip.setBrightness(BRIGHTNESS);
  strip.begin();
  strip.show();

  // Initialize SR04
  pinMode(trigPin, OUTPUT);
  pinMode(echoPin, INPUT);

  // Initialize set_dist
  set_dist = EEPROM.read(set_loc);
  // Set for testing
  // set_dist = 10;
  Serial.begin(9600);
  // This fixes a problem with the button reading high on startup
  while(digitalRead(BUTTON_PIN) == LOW){
    
  }
}

void set_lights(uint8_t distance) {
  int total_distance = max_dist - set_dist;
  /*
      We will fill up the colors first with blue,
      then green, then red when too far.
  */
  // Deterimne dist from set_dist
  int dif = distance - set_dist;
  int half_dist = (float) total_distance / 2;

  if (dif > half_dist) {
    // Set lights to be blue
    int to_lite = ((float) dif / half_dist - 1) * NUM_LEDS;
    for (int i = 0; i < NUM_LEDS; i++) {
      if (i > to_lite) {
        strip.setPixelColor(i, strip.Color(0, 0, 255, 0));
      } else {
        strip.setPixelColor(i, strip.Color(0, 0, 0, 0));
      }
    }
    strip.show();
    return;
  }
  if (dif > 0) {
    // Set lights to be blue and green
    int to_lite = ((float) dif / half_dist) * NUM_LEDS;
    for (int i = 0; i < NUM_LEDS; i++) {
      if (i > to_lite) {
        strip.setPixelColor(i, strip.Color(0, 255, 0, 0));
      } else {
        strip.setPixelColor(i, strip.Color(0, 0, 255, 0));
      }
    }
    strip.show();
    return;
  }
  if (dif <= 0) {
    // Set all lights to red
    for (int i = 0; i < NUM_LEDS; i++) {
      strip.setPixelColor(i, strip.Color(255, 0, 0, 0));
    }
    strip.show();
  }
  Serial.println(dif);

  // Setup button
  pinMode(BUTTON_PIN, INPUT_PULLUP);

}

int get_distance() {
  digitalWrite(trigPin, LOW);
  delayMicroseconds(2);
  digitalWrite(trigPin, HIGH);
  delayMicroseconds(10);
  digitalWrite(trigPin, LOW);

  duration = pulseIn(echoPin, HIGH);
  distance = (duration * .0343) / 2;
  return (int) distance;
}
void flash(uint32_t c){
    for (int i = 0; i < NUM_LEDS; i++) {
      strip.setPixelColor(i, c);
    }
    strip.show();
    delay(1000);
    for (int i = 0; i < NUM_LEDS; i++) {
      strip.setPixelColor(i, strip.Color(0, 0, 0, 0));
    }
    strip.show();
}
void loop() {
  // put your main code here, to run repeatedly:
  set_lights(get_distance());
  delay(100);

  if (digitalRead(BUTTON_PIN) == LOW){
    flash(strip.Color(0,0,0,255));
    delay(1000);
    flash(strip.Color(0,0,0,255));
    delay(1000);
    flash(strip.Color(255,0,0,0));
    set_dist = get_distance();
    EEPROM.update(set_loc, set_dist);

  }
}