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Outbyte Driver Updater FREEFix the driver behind crashes, sound loss and screen glitchesFind Drivers →Outbyte PC Repair FREEClear out junk files and repair common Windows errorsFree Scan →You can begin learning robotics without buying a board or sensor: build and test a simple Arduino parking sensor in Wokwi, a browser-based electronics simulator. Start with an HC-SR04 distance reading, then add LEDs and a buzzer to show when a virtual object is far, approaching, or close. AI can help explain or revise the sketch, but the simulator—not an AI answer—is where you check whether each change behaves as intended.
What you need to start robotics without hardware
Wokwi describes itself as an online electronics simulator and says it is free for personal use. Its supported hardware includes the Arduino Uno and HC-SR04 ultrasonic sensor, so you can assemble this project in a browser without first purchasing parts. See Wokwi’s documentation and its supported hardware list.
Create a new Arduino Uno project in Wokwi and add an HC-SR04 component. If you prefer to begin with a working reference, open Wokwi’s HC-SR04 parking sensor example. The core lesson is deliberately small: read distance, print it, and then decide how the project should respond.
How the HC-SR04 measures distance
The sensor estimates distance by sending an ultrasonic pulse and timing how long its echo takes to return. The Arduino briefly raises TRIG to start a measurement, then measures the duration of the high pulse on ECHO. Wokwi’s reference specifies a trigger pulse of at least 10 microseconds and converts the measured pulse duration to centimeters by dividing by 58. Its documented simulated distance range is 2–400 cm. See the Wokwi HC-SR04 reference.
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#1 Best Overall
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Wire the virtual sensor and optional outputs
Add the parts in Wokwi’s diagram editor and connect them as follows. The LEDs and buzzer are optional; first get the sensor reading working on its own.
| Part | Pin | Connect to |
|---|---|---|
| HC-SR04 | VCC | Arduino Uno 5V |
| HC-SR04 | TRIG | Arduino Uno digital pin 9 |
| HC-SR04 | ECHO | Arduino Uno digital pin 10 |
| HC-SR04 | GND | Arduino Uno GND |
| LEDs, optional | Anode (+) | Digital pins 4, 5, and 6, each through a current-limiting resistor |
| LEDs, optional | Cathode (−) | GND |
| Piezo buzzer, optional | Positive (+) | Arduino Uno digital pin 3 |
| Piezo buzzer, optional | Negative (−) | GND |
The sensor’s VCC, TRIG, ECHO, and GND roles are documented in the HC-SR04 reference. The output pin choices are settings for this example; keep the wiring and sketch assignments matched if you choose different pins.
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Read and print distance with a minimal sketch
Paste this into the Arduino editor. It sends the trigger pulse, measures ECHO with pulseIn, converts the duration to centimeters, and prints the result to the serial monitor.
const int trigPin = 9;
const int echoPin = 10;
void setup() {
pinMode(trigPin, OUTPUT);
pinMode(echoPin, INPUT);
Serial.begin(9600);
}
void loop() {
digitalWrite(trigPin, LOW);
delayMicroseconds(2);
digitalWrite(trigPin, HIGH);
delayMicroseconds(10);
digitalWrite(trigPin, LOW);
unsigned long duration = pulseIn(echoPin, HIGH);
float distanceCm = duration / 58.0;
Serial.print("Distance: ");
Serial.print(distanceCm);
Serial.println(" cm");
delay(200);
}The 10-microsecond trigger pulse and centimeters conversion follow Wokwi’s sensor reference. In this first version, pulseIn has no explicit timeout argument. If you later add timeout handling, test the no-echo case as well as ordinary distances so your program does not treat a missing echo as a valid reading.
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Test the sensor by changing virtual distance
- Start the simulation in Wokwi.
- Open the HC-SR04 component controls and move its distance slider.
- Watch the serial monitor as you try a far reading, a reading within your chosen warning band, and a close reading.
- Change the slider again after any code edit; confirm the output changes in the direction you expect.
The simulator’s distance control makes it possible to test several input cases without moving a physical obstacle. It verifies how your sketch responds to simulated readings; it does not establish real-world sensor accuracy.
Add distance bands, LEDs, and a buzzer
Once serial readings work, use three deliberately chosen bands to make the response visible and audible. In this example, more than 50 cm is “far,” 20–50 cm is “warning,” and less than 20 cm is “near.” These are convenient project settings, not universal parking limits or safety advice.
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Replace the first sketch with this version, then wire the optional outputs using the table above. A green LED indicates far, yellow indicates warning, and red indicates near. The buzzer is silent when far and beeps more frequently as the simulated object gets closer.
const int trigPin = 9;
const int echoPin = 10;
const int greenPin = 4;
const int yellowPin = 5;
const int redPin = 6;
const int buzzerPin = 3;
void setup() {
pinMode(trigPin, OUTPUT);
pinMode(echoPin, INPUT);
pinMode(greenPin, OUTPUT);
pinMode(yellowPin, OUTPUT);
pinMode(redPin, OUTPUT);
pinMode(buzzerPin, OUTPUT);
Serial.begin(9600);
}
void loop() {
digitalWrite(trigPin, LOW);
delayMicroseconds(2);
digitalWrite(trigPin, HIGH);
delayMicroseconds(10);
digitalWrite(trigPin, LOW);
unsigned long duration = pulseIn(echoPin, HIGH);
float distanceCm = duration / 58.0;
Serial.print("Distance: ");
Serial.print(distanceCm);
Serial.println(" cm");
digitalWrite(greenPin, LOW);
digitalWrite(yellowPin, LOW);
digitalWrite(redPin, LOW);
noTone(buzzerPin);
if (distanceCm > 50) {
digitalWrite(greenPin, HIGH);
delay(200);
} else if (distanceCm >= 20) {
digitalWrite(yellowPin, HIGH);
tone(buzzerPin, 1000);
delay(300);
noTone(buzzerPin);
delay(300);
} else {
digitalWrite(redPin, HIGH);
tone(buzzerPin, 1000);
delay(100);
noTone(buzzerPin);
delay(100);
}
}Move the slider through distances above 50 cm, between 20 and 50 cm, and below 20 cm. Confirm that the LED changes at each boundary and that the beep interval shortens in the near band. Wokwi’s community parking sensor example also changes RGB LED and speaker behavior across distance ranges, but its thresholds are an illustrative design rather than a standard: Parking Sensor With HC-SR04.
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Use AI as a tutor, then verify the code
An AI assistant can help you understand a sketch or propose a focused edit. It is not a substitute for checking the result: ask for an explanation, preserve your known-working version, and run the revised code through multiple slider positions.
- “Explain this
pulseIncode line by line.” - “Add three named distance bands without changing my pin assignments.”
- “Review this sketch for an ECHO timeout case and explain your proposed change.”
For each suggestion, compare the code with your wiring, run the simulation, and test far, warning, and near readings. If you add a third-party Arduino library, check that it works with Wokwi; its Arduino Libraries guide explains how to use libraries in projects.
What simulation can—and cannot—tell you
A successful simulation shows that the sketch runs in the simulated circuit and responds to the virtual distance control. It does not prove that a physical sensor will give the same readings, that wiring is safe, or that a vehicle installation is reliable. A 2024 paper by Auliani and co-authors describes a simulated Arduino Uno and HC-SR04 parking sensor, but a simulation is not a real-hardware accuracy test: Simulasi Sensor Parkir Berbasis Mikrokontroler Arduino Uno dengan Sensor HC-SR04 Menggunakan Website Wokwi, published online November 29, 2024.
When you are ready to extend the lesson at a desk, optional parts include an HC-SR04 sensor, an Arduino Uno-compatible board, a breadboard, jumper wires, LEDs with resistors, and a buzzer. A physical build requires separate checks of wiring, electrical limits, sensor placement, and noisy readings; none is needed to complete the browser-based exercise.
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