Lesson 6: Angles & Surfaces

Fire 20 pings at different targets - flat, soft, round, thin, tilted - and count how many echoes come back. Find out what the sensor finds hard to see.

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

• How echoes reflect like light in a mirror
• Why soft, small and tilted targets are hard to detect
• Running a fair test: change one thing at a time
• Recording results in a table

New words

Reflection

Sound bouncing off a surface. A flat surface sends it straight back if it faces the sensor.

Absorb

Soak up. Soft materials like cushions absorb sound instead of reflecting it.

Fair test

An experiment where you change only one thing, so you know what caused the difference.

What this project uses

Every item below is in the kit. Not in the box: Test objects: a flat card, a cushion or jumper, a bottle and a pencil (yours).

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

◇

a flat card

In the kit

a cushion or jumper Jumper Wire Assorted Pack 120 Pieces - Male-to-Male, Male-to-Female, Female-to-Female 10cm Ribbon Cables for… DIY-212

In the kit

◇

a bottle

In the kit

◇

a pencil (yours)

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

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

a cushion or jumper 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

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

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. a flat card, a bottle, a pencil (yours): 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 6 code. No wiring changes are needed.
2. Open the Serial Monitor at 9600 baud.
3. Put the flat card 30 cm away, square to the sensor. Wait for a row.
4. After "Change the target now", swap to the next target at the same 30 cm: card tilted about 45°, cushion, bottle, pencil.Watch out: Keep the distance the same: change only the target.
5. Copy the rows into a table or spreadsheet and compare the missed %.

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 6 of 9: Angles & Surfaces

  WIRING: the sensor from Lesson 1 (TRIG pin 9, ECHO pin 10).

  HOW TO USE IT
    Every 5 seconds the UNO fires 20 pings at the target and prints one row:
    trial, echoes_back, missed_percent, average_cm, min_cm, max_cm
    Between rows, change the target: flat card, card tilted, a cushion or
    jumper, a bottle, a pencil. Keep it at the same distance (about 30 cm).
    Open the Serial Monitor at 9600 baud.
*/

const int TRIG_PIN = 9;
const int ECHO_PIN = 10;

const int PINGS = 20;                          // pings per trial
const unsigned long GAP_MS = 5000;             // time to change the target
const unsigned long ECHO_TIMEOUT_US = 30000;
const int MIN_CM = 2;
const int MAX_CM = 400;

int trial = 0;

long readOnceCm() {
  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;
  long cm = us / 58;
  if (cm < MIN_CM || cm > MAX_CM) return 0;
  return cm;
}

void setup() {
  pinMode(TRIG_PIN, OUTPUT);
  pinMode(ECHO_PIN, INPUT);
  Serial.begin(9600);
  Serial.println("Lesson 6: Angles & Surfaces");
  Serial.println("trial,echoes_back,missed_percent,average_cm,min_cm,max_cm");
}

void loop() {
  int back = 0;
  long total = 0;
  long lowest = 9999;
  long highest = 0;

  for (int i = 0; i < PINGS; i++) {
    long cm = readOnceCm();
    if (cm > 0) {
      back = back + 1;
      total = total + cm;
      if (cm < lowest) lowest = cm;
      if (cm > highest) highest = cm;
    }
    delay(50);
  }

  trial = trial + 1;
  int missedPercent = (PINGS - back) * 100 / PINGS;
  Serial.print(trial);          Serial.print(",");
  Serial.print(back);           Serial.print(",");
  Serial.print(missedPercent);  Serial.print(",");
  if (back > 0) {
    long average = total / back;
    Serial.print(average);      Serial.print(",");
    Serial.print(lowest);       Serial.print(",");
    Serial.println(highest);
  } else {
    Serial.println("NA,NA,NA");
  }
  Serial.println("Change the target now - next trial in 5 seconds.");
  delay(GAP_MS);
}

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

• Flat card: 20 echoes back, 0% missed, steady average.
• Tilted card, cushion or pencil: fewer echoes and a bigger gap between min and max.
• A row ending in NA,NA,NA means no echo came back at all.

If it doesn't work

Small experiment

Tilt the card in steps of 15° (0°, 15°, 30°, 45°, 60°). At what angle do the echoes start to go missing?

Check what you learned

Next

• Lesson 7 smooths out noisy readings with two kinds of filter.

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