4:Submarine Sonar Beacon
Make Robot PU “Ping” like a Submarine!
Welcome to the world of Robot PU (Pair Up)! PU is more than just a toy; it is an AI-powered humanoid performer with a personality. Today, we are going to use the sonar sensor on PU’s chest to turn him into a deep-sea navigator. If time allowed, let’s play the “Don’t Bonk” game using your program with robot PU.
Knowledge: https://makecode.microbit.org/blocks/variables https://makecode.microbit.org/blocks/variables/var https://makecode.microbit.org/blocks/variables/assign https://makecode.microbit.org/blocks/variables/change https://en.wikipedia.org/wiki/Ultrasonic_transducer https://wiki.ros.org/Drivers/Tutorials/DistanceMeasurementWithUltrasonicSensorHC-SR04ArduinoI2CPython
1. Background Setup
Robot PU is an interactive STEM learning buddy controlled by a micro:bit. He is famous for his “Electrifying AI-Powered Dance”—executing moonwalks, spins, and splits with fluid motion.
But PU is also a smart explorer. He features an Autopilot Mode that lets him navigate smoothly and avoid obstacles. To do this, he uses his ultrasonic sonar sensor located right on his chest to “see” how far away walls or friends are by bouncing sound waves off them.
2. Problem Definition
We want to give PU a “Submarine Sonar” mode. Instead of just walking silently, we want PU to:
Sense the world through his chest sonar.
Sound an alarm that changes as he gets closer to something.
Create Urgency: We want the “ping” to get higher and faster as he approaches an object, just like a submarine in a movie!
3. Basic Idea of Solutions
The secret is Mapping. We will take the raw distance data from PU’s chest sensor and turn it into sound:
The Pitch: If a wall is far away, PU will play a low-pitched tone. As PU gets closer, the pitch will rise.
The Speed: We will change the timing of the “pings.” Far away means slow pings; close up means a rapid “beep-beep-beep!”.
The Brain: Because PU is powered by micro:bit, we can run this sonar logic in its own forever loop while he still moonwalks or chats.
4. Implementation
Copy this complete code into the JavaScript tab of your MakeCode editor. It includes the HCSR04 class which acts as the “driver” for PU’s chest sensor.
TypeScript
/**
* HCSR04 Driver Class for Robot PU's Chest Sonar
*/
class HCSR04 {
timeout_us: number;
trig: DigitalPin;
echo: DigitalPin;
constructor(trigPin: DigitalPin = DigitalPin.P2, echoPin: DigitalPin = DigitalPin.P8) {
this.timeout_us = 30000; // Approx 500cm max range
this.trig = trigPin;
this.echo = echoPin;
pins.digitalWritePin(this.trig, 0);
}
distance_cm(): number {
// Trigger the sensor
pins.digitalWritePin(this.trig, 0);
control.waitMicros(5);
pins.digitalWritePin(this.trig, 1);
control.waitMicros(10);
pins.digitalWritePin(this.trig, 0);
// Listen for the echo
let t = pins.pulseIn(this.echo, PulseValue.High, this.timeout_us);
if (t <= 0) t = 500;
// Convert time to cm (speed of sound)
return t * 0.0171821;
}
}
// Initialize the sonar on Robot PU's chest pins
let sonar = new HCSR04(DigitalPin.P2, DigitalPin.P8);
// Submarine Sonar Loop
basic.forever(function () {
let distance = sonar.distance_cm();
if (distance > 2 && distance < 100) {
// Map 2cm->2000Hz and 100cm->200Hz
let pitch = Math.map(distance, 2, 100, 2000, 200);
// Map 2cm->100ms and 100cm->800ms
let pulseDelay = Math.map(distance, 2, 100, 100, 800);
music.setVolume(128);
music.playTone(pitch, 50);
basic.pause(pulseDelay);
} else {
basic.pause(500);
}
});
How the HCSR04 Code Works:
- Triggering (
trig): The micro:bit sends a tiny 10-microsecond electrical pulse to PU’s chest. This tells the sensor to scream a sound too high for humans to hear. - Echo Listening (
echo): The sensor waits for that sound to bounce off a wall and return. Thepins.pulseIncommand measures exactly how many microseconds that sound was “in the air.” - The Math: Sound travels at about 343 meters per second. The code multiplies the time by
0.0171821to convert that “flight time” into centimeters. - The Timeout: If the sound never comes back (because the room is too big), the code assumes a default distance so PU doesn’t get “stuck” waiting.
5. Testing
- Download the code to the micro:bit inside your Robot PU.
- Place PU on the floor and slowly walk toward him.
- Listen to his chest! As you get closer, you should hear his pings get higher and more urgent.
- Try different objects: Does PU “see” a soft teddy bear as well as a hard wooden door? (Hint: Soft surfaces absorb sound waves!). A version with Gamepad support:
6. What Can Be Done Next?
Your PU is now a sonar expert! What else can he do?
- Scared Robot: Make PU walk backward automatically if his chest sonar detects something closer than 10cm!.
- Expressive Eyes: Use PU’s LED spotlight eyes to change colors based on distance—Green for far, Red for near.
- Talking Sonar: Combine this with the
pxt-billylibrary to have PU say “Obstacle detected!” when he gets too close.
About the “Don’t Bonk” game, here is the example program:
The key method to tweak is:
robotPu.walkDo(Math.map(distance, 8, 20, 0, 4), 0)
Would you like me to show you how to add the “Scared Robot” backward movement to the sonar loop?
You can map closer distance to negative speed (moving backwards if too close to the wall)
robotPu.walkDo(Math.map(distance, 7, 20, -1, 6), 0)
Other tricks to win the game:
- How adjust the mapping function to map the sonar distance to speed
- How to smooth the sonar distance values to avoid measurement outliers and errors
- How to feed forward to handle sensor delays.
To make movement more smoothly, move the walk command to a dedicated forever loop. It make robot PU walk and play beeps at same time.
How to win the Don’t Bonk Game
The basic idea is to get distance and walk, do not add any other code to slow down the observe-think-action loop.