Lesson 4: Blind Zone & No Echo

Find out where the sensor fails: too close, too far, too soft or at an angle. The LEDs and the Serial Monitor count each kind of reading.

One of 9 projects in the Arduino Ultrasonic Distance & Parking Learning Kit — the parts below are from that kit.

Before you start

What you build and learn

• The blind zone right in front of the sensor
• Why a missing echo is not the same as "nothing there"
• Counting results with variables
• Typing a command into the Serial Monitor

New words

Blind zone

The space just in front of the sensor (about 2-3 cm) where it cannot measure properly.

Timeout

How long the code waits before giving up. Here 30 ms: after that we call it "no echo".

Variable

A named box that holds a number, such as goodCount. It can change while the sketch runs.

What this project uses

Every item is in the kit — nothing extra to buy.

UNO R3 UNO R3 Development Board ATmega328P Microcontroller with USB Cable, 5V Logic, 14 Digital I/O, 6 Analog Inputs… UNOR3

In the kit

HC-SR04 HC-SR04 Ultrasonic Distance Sensor Module for Arduino, Raspberry Pi & DIY Robotics Projects, 5V Trigger/Echo… DIY-00043

In the kit

◇

red/yellow/green LEDs

In the kit

◇

Serial Monitor

In the kit

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the wiring from Lesson 3

In the kit

Basics 400 Tie Point Solderless Breadboard - Half Size Prototyping Circuit Board with Power Rails, for Arduino & Ele… DIY-238

In the kit

Basics Jumper Wire Assorted Pack 120 Pieces - Male-to-Male, Male-to-Female, Female-to-Female 10cm Ribbon Cables for… DIY-212

In the kit

Build this with

Arduino Ultrasonic Distance & Parking Learning Kit

All 9 parts in one box, with this project and 8 more to build from them.

AED 85.00 See the kit Add kit to cart

Need only these parts? Order them loose · from AED 78.30 ▾

Used in this project tick what you still need

UNO R3 UNO R3 Development Board ATmega328P Microcontroller with USB Cable, 5V Logic, 14 Digital I/O, 6 Analog Inputs… UNOR3 · ×1

AED 26.39

In stock

HC-SR04 HC-SR04 Ultrasonic Distance Sensor Module for Arduino, Raspberry Pi & DIY Robotics Projects, 5V Trigger/Echo… DIY-00043 · ×1

AED 15.31

In stock

Also needed untick if you already have them

Basics 400 Tie Point Solderless Breadboard - Half Size Prototyping Circuit Board with Power Rails, for Arduino & Ele… DIY-238 · ×1

AED 11.58

In stock

Basics Jumper Wire Assorted Pack 120 Pieces - Male-to-Male, Male-to-Female, Female-to-Female 10cm Ribbon Cables for… DIY-212 · ×1

AED 25.02

In stock

Selected parts AED 78.30

Add 4 parts to cart

One of each part. Packs (resistor assortment, jumper wires) already hold more than a single build needs. red/yellow/green LEDs, Serial Monitor, the wiring from Lesson 3: included in the kit, ask us for it loose. Delivery is AED 20, free on orders AED 100+.

Connections

Unplug USB before you change any wire. Pin names are the labels printed on the board.

Step by step

One thing at a time. Tick nothing off until it matches the diagram.

1. Upload the Lesson 4 code. No wiring changes are needed.
2. Open the Serial Monitor at 9600 baud with "New Line" selected.
3. Type r and press Enter. Hold a book 30 cm away for 10 seconds: green, and the good count goes up.
4. Type r. Move the book right up to the sensor, 1-2 cm away. Watch for yellow (too close) or red - and wrong numbers.
5. Type r. Point the sensor at a cushion or a soft jumper 30 cm away, then at a pencil, then at the book tilted to 45°.
6. Type r. Point the sensor at an empty part of the room. Write down the counts after 10 seconds for each test.

Sketch for this project

Written for the board in the kit. Copy it into the Arduino IDE; change the pin numbers if you wire it differently.

/*
  DIY KIT - Arduino Ultrasonic Distance & Parking Learning Kit
  Lesson 4 of 9: Blind Zone & No Echo

  WIRING: the sensor and LEDs from Lessons 1-3 (pins 5, 6, 7, 9, 10).
  The buzzer can stay connected - this sketch keeps it silent.

  IN THIS LESSON THE LEDs MEAN SOMETHING DIFFERENT:
    Green  = a good reading
    Yellow = too close (under 3 cm) - the sensor's "blind zone"
    Red    = no echo came back (too far, too soft, or angled away)
  The Serial Monitor (9600 baud) counts each kind of reading.
  Type r and press Enter to set the counts back to 0.
*/

const int RED_LED = 5;
const int YELLOW_LED = 6;
const int GREEN_LED = 7;
const int BUZZER_PIN = 8;
const int TRIG_PIN = 9;
const int ECHO_PIN = 10;

const int BLIND_CM = 3;                        // closer than this is the blind zone
const unsigned long ECHO_TIMEOUT_US = 30000;   // after 30 ms we call it "no echo"
const int MAX_CM = 400;

int goodCount = 0;
int blindCount = 0;
int noEchoCount = 0;

// Distance in cm, or 0 if no echo came back in time.
long readRawCm() {
  digitalWrite(TRIG_PIN, LOW);
  delayMicroseconds(2);
  digitalWrite(TRIG_PIN, HIGH);
  delayMicroseconds(10);
  digitalWrite(TRIG_PIN, LOW);
  unsigned long us = pulseIn(ECHO_PIN, HIGH, ECHO_TIMEOUT_US);
  if (us == 0) return 0;
  return us / 58;
}

void setup() {
  pinMode(RED_LED, OUTPUT);
  pinMode(YELLOW_LED, OUTPUT);
  pinMode(GREEN_LED, OUTPUT);
  pinMode(BUZZER_PIN, OUTPUT);
  digitalWrite(BUZZER_PIN, LOW);   // keep the buzzer quiet in this lesson
  pinMode(TRIG_PIN, OUTPUT);
  pinMode(ECHO_PIN, INPUT);
  Serial.begin(9600);
  Serial.println("Lesson 4: Blind Zone & No Echo");
}

void loop() {
  // Type r + Enter to reset the counts.
  while (Serial.available() > 0) {
    char c = Serial.read();
    if (c == 'r' || c == 'R') {
      goodCount = 0;
      blindCount = 0;
      noEchoCount = 0;
      Serial.println("Counts reset");
    }
  }

  long cm = readRawCm();
  bool noEcho = (cm == 0 || cm > MAX_CM);
  bool blind = (!noEcho && cm < BLIND_CM);
  bool good = (!noEcho && !blind);

  digitalWrite(RED_LED, noEcho ? HIGH : LOW);
  digitalWrite(YELLOW_LED, blind ? HIGH : LOW);
  digitalWrite(GREEN_LED, good ? HIGH : LOW);

  if (noEcho) noEchoCount++;
  else if (blind) blindCount++;
  else goodCount++;

  Serial.print("cm=");
  if (noEcho) Serial.print("none");
  else Serial.print(cm);
  Serial.print("  good=");
  Serial.print(goodCount);
  Serial.print("  too_close=");
  Serial.print(blindCount);
  Serial.print("  no_echo=");
  Serial.println(noEchoCount);

  delay(200);
}

Upload it

1. Click Copy (or Download .ino and open the file).
2. In the Arduino IDE choose File → New Sketch, select everything in it and paste.
3. Check the bottom of the window says Arduino Uno and your port (Start here, step 5).
4. Click Upload (the → arrow) and wait for Done uploading.

How the code works

Change it and see

What you should see or hear

• Green and climbing good counts with a flat book 30 cm away.
• Right up close: yellow, red, or a number that is clearly wrong.
• Soft, thin or tilted targets: more red (no echo), even though something is there.

If it doesn't work

Small experiment

Make a table: book, cushion, pencil, tilted book, empty room. For each, write good / too close / no echo after 10 seconds. Which target is hardest for the sensor?

Check what you learned

Next

• Lesson 5 measures exactly how accurate your sensor is, with a ruler and a spreadsheet.

Hi DIY KIT, I'm stuck on the Arduino Ultrasonic Distance & Parking Learning Kit.
Lesson: __
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