Lesson 8 Young Roboticists (Ages 8-11)

Echolocation: Ultrasonic Distance Sensors (HC-SR04)

Track 6: Robotics, Physical Computing & Autonomous AI

The Mission Hook

Bats fly through pitch-black caves at 30 miles per hour without touching a single stalactite by screaming ultrasonic shouts and listening for the echo. Today, we equip our robot with bat echolocation!

Mission Toolkit: Required Course Software & Web Platforms

Interactive Rangefinder Sandbox Free Student Sandbox

Tinkercad Ultrasonic Sonar

Simulate HC-SR04 sonar with draggable physical target and live centimeter readout.

Setup Checklist:
• Search components for 'Ultrasonic Distance Sensor (4 pin)'.
• Connect VCC to 5V (or 3V), GND to GND, TRIG to Pin 0, ECHO to Pin 1.
• Click the sensor during simulation to drag the test obstacle target.

Launch & Configure Tinkercad Ultrasonic Sonar

Use Arrow Keys or Space to advance • Press 'T' or 'S' for Tutor Cockpit

The Big Idea: Ultrasonic Waves, Speed of Sound, Pulse Timing, and Distance Math

Explore the essential building blocks for this lesson:

Concept Watch: How Ultrasonic Sensors Work (HC-SR04 Deep Dive)

2:20 Micro-Video Watch on YouTube

Video not loading? Open it directly: Watch on YouTube ↗

What to Look For:

• A 10-microsecond trigger pulse initiates eight 40kHz sonic burst cycles.

• Echo pin output duration directly corresponds to time-of-flight through the air.

• Target material density, angle of incidence, and ambient temperature affect accuracy.

The HC-SR04 Sensor

The sensor features two metallic cylinders: one is a miniature speaker sending 40kHz sound bursts (Trigger), and the other is a microphone waiting for the echo (Echo).

Speed of Sound Math

Sound travels through air at 343 meters per second (about 0.0343 cm per microsecond). By timing how long the echo took, dividing by 2 gives exact distance!

Blind Spots & Echo Deflections

Ultrasonic sensors work best on flat hard surfaces from 2cm to 400cm. Soft curtains absorb the sound, and sharp angles can bounce the echo away.

Guided Co-Pilot Activity

Follow the three steps in order. Stuck? Ask your mentor for a hint, not the answer.

Wire & Inspect the Virtual Circuit

Open the simulator and wire Trigger to Pin 0 and Echo to Pin 1.

Action: Open the hardware simulator, check pin wiring, power rails, and common ground

Flash the Microcontroller Code

Write the 10 microsecond trigger pulse and calculate distance using duration * 0.0343 / 2.

Action: Type the MicroPython control logic, sensor thresholds, and safety limits

Simulate, Measure & Tune

Slide the virtual target back and forth in the simulator to see centimeters update in real time.

Action: Run the simulation, adjust virtual sensor sliders, and verify actuator output

Python Snippet

from microbit import * import machine # Ultrasonic Distance Calculation in Centimeters # Trigger Pin: Pin 0, Echo Pin: Pin 1 def get_distance_cm(): pin0.write_digital(0) sleep_us(2) # Send 10 microsecond ultrasonic burst pin0.write_digital(1) sleep_us(10) pin0.write_digital(0) # Measure duration echo pin stays HIGH in microseconds duration = machine.time_pulse_us(pin1, 1, 30000) if duration < 0: return 999 # Timeout / nothing in range # Distance = (time * speed of sound 0.0343 cm/us) / 2 (round trip) distance_cm = (duration * 0.0343) / 2 return round(distance_cm, 1) while True: dist = get_distance_cm() display.scroll(str(int(dist)) + "cm", delay=60) sleep(100)

Robotics Hardware & Telemetry Console

BBC micro:bit v2 / ESP32 Simulator

>>> flash --target microbit_v2 main.py

[HC-SR04 Sonar] Trigger Pin0: 10us ultrasonic burst @ 40kHz
[Echo Pin1] Time-of-Flight duration = 1420 microseconds
[Distance Math] (1420us * 0.0343 cm/us) / 2 = 24.4 cm

Hardware Simulation Verified (Exit 0) Bus: 3.3V Logic / Common GND

Checkpoint Challenge

Demonstrate your understanding before starting your solo quest:

Why do we divide the ultrasonic travel time by 2 when calculating obstacle distance?

Your Solo Quest

Choose your achievement level and take the wheel:

Interactive Quest Checklist (Click to Claim):

0 / 350 XP

Bronze • +50 XP

First Step

Simulate an ultrasonic sensor and print accurate centimeter measurements to the console.

Silver • +100 XP

Skill Practice

Build an automatic collision warning: display a smiley face when distance > 30cm, and a skull when < 10cm.

Gold • +200 XP

Creative Challenge

Add an auditory backup beeper that beeps faster the closer an obstacle gets.

Lesson Summary & Practice

Celebrate your progress and prepare for your next level:

60-Second Show and Tell

Present your screen to your mentor and explain:
• What did you build today?
• Which challenge did you solve?

Take-Home Project: Ultrasonic Tape Measure & Parking Assistant

25 Mins • Independent Practice

The Challenge: Build a parking distance assistant: 3 green LEDs for far, 2 yellow for medium, and 1 flashing red with buzzer when within 5cm!

Build: Create 3 distance zones using if-elif-else logic.

Self-Test: Trigger the buzzer when distance drops below 10cm.

Turn In: Upload your distance zone table and code to Google Classroom.

Lesson Completed!

Continue to Lesson 9: Smart Bumper Bot

[STEMulus Home Mission] Lesson 8: Echolocation: Ultrasonic Distance Sensors (HC-SR04) Course: Track 6: Robotics, Physical Computing & Autonomous AI (Young Roboticists (Ages 8-11)) Estimated Time: 25 Mins (Independent Practice) Mission Challenge: Build a parking distance assistant: 3 green LEDs for far, 2 yellow for medium, and 1 flashing red with buzzer when within 5cm! Action Steps: 1. Build: Create 3 distance zones using if-elif-else logic. 2. Self-Test: Trigger the buzzer when distance drops below 10cm. 3. Turn In: Upload your distance zone table and code to Google Classroom. Showcase: Bring your project to our next session for a 3-minute screen-share celebration!